User's Guide
WinProp Phase Property Program Version 2010
By Computer Modelling Group Ltd.
This publication and the application described in it are furnished under license exclusively to the licensee, for internal use only, and are subject to a confidentiality agreement. They may be used only in accordance with the terms and conditions of that agreement. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic, mechanical, or otherwise, including photocopying, recording, or by any information storage/retrieval system, to any party other than the licensee, without the written permission of Computer Modelling Group. The information in this publication is believed to be accurate in all respects. However, Computer Modelling Group makes no warranty as to accuracy or suitability, and does not assume responsibility for any consequences resulting from the use thereof. The information contained herein is subject to change without notice.
Copyright © 1987-2010 Computer Modelling Group Ltd. All rights reserved.
The license management portion of this program is based on: Reprise License Manager (RLM) Copyright (C) 2006-2010, Reprise Software, Inc WinProp uses Intel(R) Compilers. WinProp, CMG, and Computer Modelling Group are registered trademarks of Computer Modelling Group Ltd. All other trademarks are the property of their respective owners. Computer Modelling Group Ltd. Office #150, 3553 - 31 Street N.W. Calgary, Alberta Canada T2L 2K7
Tel: (403) 531-1300
Fax: (403) 289-8502
E-mail:
[email protected]
Preface WinProp is CMG's equation of state (EOS) multiphase equilibrium and properties determination program. WinProp features techniques for characterizing the heavy end of a petroleum fluid, lumping of components, matching laboratory PVT data through regression, simulation of first and multiple contact miscibility, phase diagrams generation, asphaltene and wax precipitation modelling, compositional grading calculations as well as process flow simulation. This User's Guide presents a comprehensive description of the steps involved in obtaining a PVT data suitable for inclusion in data files for CMG's GEM, STARS or IMEX simulators. This User's Guide is aimed at reservoir engineers who want to use WinProp to predict phase behavior of reservoir fluids as well as characterize these fluids for reservoir simulation. It requires some knowledge of phase behavior as it pertains to the different fluid types found in reservoirs. Every attempt has been made in the preparation of this User's Guide to provide the user with all the necessary details. If questions arise, please contact: Computer Modelling Group Ltd. #150, 3553 – 31 Street N.W. Calgary, Canada T2L 2K7 Telephone: (403) 531-1300 Fax: (403) 289-8502 E-mail:
[email protected]
Confidentiality: All components of CMG technology including software and related documentation are protected by copyright, trademark and secrecy. CMG technology can be used only as permitted by your license from CMG. By the license, you have agreed to keep all CMG technology confidential and not disclose it to any third party. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic, mechanical, or otherwise, including photocopying, recording, or by any information storage/retrieval system, to any party other than the licensee, without the written permission of Computer Modelling Group. Corrections/Errors: CMG ENDEAVORS TO PRODUCE TECHNOLOGY OF THE HIGHEST QUALITY; NEVERTHELESS ERRORS OR DEFICIENCIES IN SUCH TECHNOLOGY ARE INEVITABLE. IF YOU FIND AN ERROR OR DEFICIENCY, YOU ARE REQUESTED TO PROVIDE DETAILS OF IT AND ILLUSTRATIVE DATA SET(S) TO CMG SUFFICIENT TO PERMIT CMG TO REPRODUCE THE ERROR OR DEFICIENCY. CMG SHALL ENDEAVOR TO REMEDY A DEFICIENCY IN A TIMELY MANNER AND SHALL PERIODICALLY REPORT TO YOU AS TO THE STEPS BEING TAKEN TO REMEDY THE DEFICIENCY. THE RESPONSE TIME FOR A DEFICIENCY MUST BE PRIORITIZED FOR THEIR GENERAL APPLICATION TO CMG MEMBERS AND WHETHER THEY FORM PART OF A CMG PROGRAM. CMG DOES NOT WARRANT THAT DEFICIENCIES WILL BE REMEDIED.
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Contents New Features
1
New Features in WinProp 2010.10...............................................................................1 New Features in WinProp 2009.10...............................................................................1 New Features in WinProp 2008.10...............................................................................2 New Features in WinProp 2007.10...............................................................................2 New Features in WinProp 2006.10...............................................................................3 New Features in WinProp 2005.10...............................................................................3 New Features in WinProp 2004.10...............................................................................4 New Features in WinProp 2003.11...............................................................................4 New Features in WinProp 2003.10...............................................................................5 New Features in WinProp 2002.10...............................................................................6 New Features in WinProp 2001.10...............................................................................6 New Features in WinProp 2000.15...............................................................................7 New Features in WinProp 2000.10...............................................................................8 New Features in WinProp 1999.10...............................................................................9 New Features in WinProp 98.00.................................................................................12 New Features in WinProp 97.00.................................................................................14
Introduction
17
What is WinProp?.......................................................................................................17 Use of this Manual......................................................................................................18 Installation ..................................................................................................................18 Confidentiality ............................................................................................................18 Template Data Files ....................................................................................................19
Tutorial Section
21
Overview.....................................................................................................................21 Getting On-Line Help .................................................................................................21 Creating, Opening and Saving Data Files...................................................................21 Running, Viewing Output and Creating Plots ............................................................22 Copying Between Different Data Files.......................................................................23 Setting Up a Regression Run ......................................................................................23
User's Guide WinProp
Contents • i
Using the Update Component Properties Feature of WinProp................................... 23 View the Keyword Data File Created by WinProp .................................................... 24 Selecting a User-Defined Editor................................................................................. 24 Editing the Data Set.................................................................................................... 24 Table Import Wizard .................................................................................................. 25 Overview ....................................................................................................... 25 Using the Table Import Wizard..................................................................... 26
Data Set Structure
31
Overview .................................................................................................................... 31 Editing Data Set.......................................................................................................... 32
Titles/EOS/Units Selection
33
Overview .................................................................................................................... 33 Data Input ................................................................................................................... 33 Comments...................................................................................................... 33 Title 1, Title 2, Title 3 ................................................................................... 33 Equation of State ........................................................................................... 34 Units .............................................................................................................. 34 Feed ............................................................................................................... 34
Components
35
Component Selection and Definition ......................................................................... 35 Library Components...................................................................................... 35 User Component with Known Properties...................................................... 36 User Component with Known SG, Tb and MW ............................................ 37 Component Properties ................................................................................................ 38 Notes on Component Properties.................................................................... 39 Interaction Coefficients .............................................................................................. 43 Hydrocarbon-Hydrocarbon Interaction Coefficients..................................... 44 Other Interaction Coefficients ....................................................................... 46 Viscosity Parameters .................................................................................................. 46 Jossi-Stiel-Thodos Correlation ...................................................................... 46 Pedersen Correlation ..................................................................................... 47 Aqueous Phase ........................................................................................................... 48 Aqueous Phase Salinity ................................................................................. 48 Henry’s Law Constant Correlation................................................................ 49 Activation of Second Set of Component Properties................................................... 49 GEM Fluid Model Generation and Component Properties Printing .......................... 50 Importing Components with the Table Import Wizard .............................................. 51
ii • Contents
User's Guide WinProp
Common Data Required for All Options
53
Overview.....................................................................................................................53 Composition Specification..........................................................................................53 Initial K-Values...........................................................................................................55 Output Level ...............................................................................................................55 Stability Test Level.....................................................................................................55
Two-Phase Saturation and Phase Boundary Calculations
57
Overview.....................................................................................................................57 Saturation Pressure .....................................................................................................57 Saturation Temperature...............................................................................................58 Phase Boundary and Quality Line Calculations .........................................................58 Envelope Specification ..................................................................................59 Envelope Construction Controls ....................................................................61 Cricondenbar/Cricondentherm Calculation ................................................................62 Critical Point Calculation............................................................................................62
Flash Calculations
63
Overview.....................................................................................................................63 Common Input for Two-Phase Flash, Multiphase Flash and Asphaltene/Wax Modelling Calculations...............................................................................................63 Two-Phase Flash Calculations....................................................................................64 Multiphase Flash Calculations....................................................................................64 Asphaltene/Wax Modelling ........................................................................................65 Theoretical Background.................................................................................65 Input Data - Asphaltene/Wax Modelling.......................................................67 Single-Phase Calculation ............................................................................................70 Isenthalpic Flash Calculations ....................................................................................70 Theoretical Background.................................................................................70 Input Data - Isenthalpic Flash ........................................................................72
Three-Phase Boundary Calculation
73
Background.................................................................................................................73 Input Data ...................................................................................................................73 Envelope Specification Tab ...........................................................................73 Envelope Construction Controls Tab.............................................................75 Initial K-Values Tab ......................................................................................76
User's Guide WinProp
Contents • iii
Component Splitting and Lumping
77
Overview .................................................................................................................... 77 Characterization of Multiple Related Samples........................................................... 78 Splitting the "Plus" Fraction....................................................................................... 78 Importing Extended Analysis Data with the Table Import Wizard............................ 82 Numerical Cleaning of Mud-Contaminated Samples................................................. 83 Lumping of Components............................................................................................ 84 Transferring Results to Other Data Sets ..................................................................... 85
Laboratory Calculations
87
Overview .................................................................................................................... 87 Recombination of Separator Oil and Gas................................................................... 87 Compressibility Calculation ....................................................................................... 90 Constant Composition Expansion .............................................................................. 90 Differential Liberation................................................................................................ 92 Constant Volume Depletion ....................................................................................... 94 Separator Test............................................................................................................. 97 Swelling Test............................................................................................................ 101 Importing Laboratory Experiment Data with the Table Import Wizard................... 103
Multiple Contact Miscibility Calculations
105
Overview .................................................................................................................. 105 Data Input ................................................................................................................. 106
Regression
111
Overview .................................................................................................................. 111 Organization of the Input Data ................................................................................. 111 Parameter Selection.................................................................................................. 112 Automatic Regression Parameter Selection ............................................................. 114 Grouping Regression Variables................................................................................ 114 Regression Variable Bounds .................................................................................... 115 Regression Control Parameters ................................................................................ 116 Transferring Results to Other Data Sets ................................................................... 116
Compositional Grading
119
Overview .................................................................................................................. 119 Data Input ................................................................................................................. 120
iv • Contents
User's Guide WinProp
STARS PVT Data Generation
123
Overview...................................................................................................................123 Use of the STARS PVT Generation Option .............................................................123 Input Data (STARS) .................................................................................................124 Basic STARS PVT Data ..............................................................................124 Gas-Liquid K-Value Tables.........................................................................126 Gas-Liquid and Liquid-Liquid K-Value Tables ..........................................127 Gas-Liquid and Solid-Liquid K-Value Tables.............................................128 Feed and K-Value Plotting Controls............................................................129
Process Flow
131
Overview...................................................................................................................131 Data Input - Process Flow.........................................................................................132
Black-Oil PVT Data Generation
135
Overview...................................................................................................................135 Laboratory Procedure ...............................................................................................144 Input Data .................................................................................................................144
References
149
List ............................................................................................................................149
Appendix A
153
Case Studies..............................................................................................................153 Case Study Number 1: Gas Condensate Modelling....................................153 Case Study Number 2: Solubility of CO2 in Brine .....................................163 Case Study Number 3: Asphaltene Precipitation Modelling ......................174
Appendix B
183
Equations ..................................................................................................................183 Cubic Equation of State ...............................................................................183 Phase Stability Test......................................................................................188 Two-Phase Flash Calculation ......................................................................190 Saturation Calculation..................................................................................191 Cricondenbar/Cricondentherm Equations....................................................193 Phase Diagram Construction .......................................................................193 Three Phase Flash Calculation with Equation of State ................................197 Three Phase with Isenthalpic Flash Calculation ..........................................198 Flash Calculation Involving Water ..............................................................200
User's Guide WinProp
Contents • v
Critical Point Calculations........................................................................... 203 Viscosity Correlation................................................................................... 204 Solution of Non-Linear Equations .............................................................. 206 Plus Fraction Characterization .................................................................... 207 Interfacial Tension Calculations.................................................................. 211 Regression ................................................................................................................ 211 Introduction ................................................................................................. 211 The Regression Method............................................................................... 212 Application of the Regression ..................................................................... 213 Properties of Components ........................................................................................ 216 User Components ........................................................................................ 218 Interaction Coefficient................................................................................. 220 Nomenclature ........................................................................................................... 222 References for Appendix B ...................................................................................... 224
vi • Contents
User's Guide WinProp
New Features
New Features in WinProp 2010.10 New Approach for the Multiple Contact Miscibility Calculation A Tie Line calculation method has been added to WinProp in the Multiple Contact Miscibility Calculation section to calculate the minimum miscibility pressure (MMP) or minimum miscibility enrichment (MME). This method takes the combined condensing and vaporizing displacement mechanisms into consideration, as well as the existing pure vaporizing or pure condensing mechanisms. With the pressure or enrichment increasing, all key tie lines, including the initial tie line, injection tie line and the crossover tie lines, can be found simultaneously based on the method of characteristics theory. The MMP or MME can be determined once any of these key tie lines’ length becomes zero. Please see the Multiple Contact Miscibility Calculation section of the User’s Guide for more details. Use of the feature is illustrated in the mcm-combined-U2002rich-MMP.dat template data set. Liquid Viscosity-Temperature Table for Multiple Pressures The STARS PVT generation option can now calculate and output multiple liquid viscositytemperature tables over a defined pressure range. This is compatible with a new STARS option to allow pressure dependence of liquid viscosities available in STARS 2010.10.
New Features in WinProp 2009.10 Numerical Cleaning of Mud-Contaminated Samples A new feature has been added to WinProp in the Component Splitting and Lumping section. WinProp now can determine the original composition of the reservoir fluids from mudcontaminated samples. WinProp uses the skimming method, subtraction method or a combination of both methods to numerically clean the mud-contaminated samples. If the level of mud contamination is available and the mud composition is also provided, a direct subtraction method will be used to numerically clean the contaminated sample. If the level of mud contamination is not available but the mud composition is provided, a combination of the skimming method and subtraction method will be used to estimate the level of contamination first, and then numerically clean the contaminated sample. If there is no information about the level of contamination and mud composition, WinProp can use skimming method to numerically clean the contaminated sample based on the first and last SCN in the mud. Please see the Component Splitting and Lumping section of the User’s Guide for more details. Use of the feature is illustrated in the mudclean_split.dat template data set.
User's Guide WinProp
New Features • 1
New Features in WinProp 2008.10 STARS PVT Generation A number of enhancements have been made to improve the liquid density parameters. The feed composition is flashed at reference pressure and temperature so that a stable liquid composition is used for all calculations. Once this is done, Compressibility, first and second thermal expansion coefficients are determined from a perturbation calculation. Finally the cross coefficient (P and T) is determined by optimization to best fit surface conditions and a userspecified range of reservoir condition densities. These changes result in a decreased sensitivity to the choice of reference conditions, more accurate compressibility parameters, and a better match between the EOS and STARS fluid model densities, which are now shown in a table in the .out file. The reference phase for components can now be specified as AQUEOUS, the previous default was that all components are OLEIC. This means that K-values for gas-water systems can be generated. In addition, the solid K-value table generation has been improved, as well as the map of WinProp EOS vs. STARS k-value flash results. Aqueous Phase Property Models Accurate models for the Henry’s constants of CO2, N2, H2S and CH4 have been implemented, taking into account pressure, temperature and salinity (salting-out coefficient). These models are activated by selecting the option button for “Harvey’s Method (1996)” on the “Aqueous phase” tab of the Component properties dialog. These correlations are also implemented in GEM 2008.10. The existing aqueous phase solubility models are still available in WinProp. The Kestin correlation is now used for aqueous phase viscosity when the OGW flash is specified in WinProp. Calculation of Temperature-Dependent Asphaltene Parameters It is now possible to enter multiple asphaltene onset pressures at different temperatures in the asphaltene flash dialog. These values are used to calculate the temperature-dependent parameters of the asphaltene precipitation model.
New Features in WinProp 2007.10 IMEX Volatile Oil PVT Table Generation Black oil PVT tables can be generated for the new IMEX volatile oil option. Undersaturated gas compressibility and viscosity may be represented using only the dry gas and saturated gas endpoints, or with a complete table of values between these endpoints. The “endpoints” form uses the new PVTVO table. To allow modelling of nonlinear effects in the gas compressibility and viscosity, undersaturated gas property tables are used in conjunction with the PVTCOND table, as for the Gas-Water with Condensate model in IMEX.
2 • New Features
User's Guide WinProp
Other Enhancements for IMEX PVT Table Generation For all IMEX PVT tables, the user can now choose to generate gas formation volume factors, gas expansion factors, or gas Z-factors. This applies to the saturated tables (PVT, PVTG, PVTCOND and PVTVO) as well as the undersaturated gas tables, which can now take the form BGUST, EGUST or ZGUST. For IMEX PVTCOND and PVTVO tables, calculation of the condensate/gas ratio at low pressures has been modified for improved performance in the simulator. Scaling Differential Liberation Oil FVF and GOR to Bubble Point Oil Volume For the differential liberation experiment, oil formation volume factor and solution gas/oil ratio can be scaled to the bubble point oil volume rather than the residual oil volume. This provides oil shrinkage and cumulative gas released per volume of bubble point oil, and eliminates the need for the EOS to accurately represent the residual oil volume. The scaled values can be used in regression. Summary plots show both the original data and the scaled values. STARS PVT Generation For STARS PVT generation, new methods have been implemented to generate the component liquid viscosity table. Apparent liquid viscosities of light components can be generated by perturbing the dead oil at each temperature, which will give accurate liquid viscosities of solvent components which may vaporize at higher temperatures ("match dead oil" method). Smooth curves for all component viscosities may be generated by scaling the liquid viscosities at low temperatures, then extrapolating to higher temperatures ("scale viscosities" method). More accurate determination of phase viscosity and density, and reduced sensitivity to choice of reference condition, have been achieved by using stable liquid properties in STARS component property calculations. Saturation Pressure/Regression Enhancement Saturation Pressure calculation results are checked for stability. This prevents the regression algorithm from converging to an unstable two-phase saturation condition, within a three-phase region.
New Features in WinProp 2006.10 Enhancements of existing features and code clean up.
New Features in WinProp 2005.10 A number of WinProp’s calculation options have been enhanced, including the following: Irreversible Asphaltene Calculation The asphaltene flash has been enhanced to allow specification of an equilibrium constant for conversion of reversible to irreversible asphaltene. The irreversible asphaltene can be interpreted as flocculated solid particles. This technique has been designed to allow the simulation of laboratory forward and reverse contact experiments with series of asphaltene flash calculations.
User's Guide WinProp
New Features • 3
Oil-Gas-Water (OGW) Flash Calculations The OGW flash has been improved to give greater stability and better convergence characteristics for difficult problems, for example light and intermediate hydrocarbons with steam. STARS Aqueous-Liquid and Aqueous-Vapor K-Value Generation In addition to the improvements of the OGW flash listed above, the generation of STARS Kvalues including aqueous phases has been enhanced with improved extrapolation algorithms.
New Features in WinProp 2004.10 A number of WinProp’s calculation options have been enhanced, including the following: Compositional Gradient Calculation For the non-isothermal model, temperatures are now output to the summary table, error trapping has been improved, and the input of the temperature gradient has been modified so that positive gradient values now indicate increasing temperature with depth. Viewing Simulator PVT Models Menu items have been added to allow easy viewing of the files generated for GEM, IMEX or STARS component models, analogous to the WinProp output file viewing procedure. Temperature-Dependent Volume Shifts The Rackett’s Z-Factor is now re-calculated during lumping or regression calculations, so that the temperature-dependent volume shift technique will maintain consistency with pseudocomponent specific gravities. STARS PVT Model Generation Liquid-phase component viscosities for light components are now back-calculated from live oil and dead oil viscosities, rather than computing them directly from the WinProp viscosity model.
New Features in WinProp 2003.11 Gamma Distribution Characterization Enhancements The following enhancements have been implemented for the gamma distribution characterization: (1) Specification of the bounds on the molecular weights has been improved when using the “variable molecular weight interval” method for fitting the distribution parameters to extended analysis data. (2) When specific gravity data is available with the extended analysis, coefficients in the specific gravity-molecular weight correlation are adjusted to best fit the data. (3) Use of the gamma distribution to extrapolate extended analysis data to higher carbon numbers has been improved to provide better consistency with input physical property data.
4 • New Features
User's Guide WinProp
Separator Calculation for Gas Condensates Calculation of dry gas and wet gas formation volume factors has been implemented when the separator calculation is used with gas condensate fluids. The dry gas FVF is defined as the volume of gas at the dew point pressure divided by the volume of gas from all separator stages evaluated at standard conditions. The wet gas FVF is defined as the volume of gas at the dew point pressure divided by a hypothetical surface wellstream volume, calculated under the assumption the entire wellstream is in the gas phase with a Z-factor of one. The condensate/gas ratio is also reported. In addition, the average separator gas gravity from all separation stages is now being output for oil and condensate fluids.
New Features in WinProp 2003.10 IMEX GASWATER_WITH_CONDENSATE PVT Table Generation The black oil PVT option has been expanded to allow generation of PVT tables for the IMEX GASWATER_WITH_CONDENSATE fluid model. This model allows description of condensate liquid dissolved in the gas phase or present as a free liquid in the reservoir and at surface conditions. This option may be used for dewpoint fluids (gas condensates) only. The tables are generated by simulating a constant volume depletion experiment. For each pressure level in the constant volume depletion, a row in the *PVTCOND table for the saturated properties is written. Individual *BGUST and VGUST tables are written for the gas formation volume factors and gas viscosities corresponding to each saturation pressure in the *PVTCOND table. Use of the feature is illustrated in the imex_condensate.dat template data set. Regression on Secondary Stream Mole Fraction The ability to select the mole fraction of the secondary stream, used to define the feed composition for a calculation option, has been added to the regression calculation. The feed composition can be defined as a mole fraction weighted mixture of the primary and secondary compositions. This mole fraction can be adjusted during regression to match any of WinProp’s allowable experimental data types. One application of this feature is to determine the mole fraction of a separator gas stream necessary to recombine with a separator oil stream to achieve a specified GOR. Use of this feature is illustrated in the template data set regress_stream-frac.dat. Automatic Selection of Regression Parameters For users with limited experience in tuning equation of state parameters to match experimental data, a facility is provided to automatically select regression parameters based on the types of experimental data entered in the calculation options within the regression block. WinProp will select a combination of critical properties of the heavy end pseudocomponents, volume shift parameters, hydrocarbon binary interaction parameter exponents and viscosity parameters to be adjusted during regression, depending on the experimental data entered. The automatic parameter selector will not remove any parameters already selected by the user. Also, once the automatic parameter selection process is complete, you may add or remove regression parameters manually.
User's Guide WinProp
New Features • 5
New Features in WinProp 2002.10 Minimum Miscibility Enrichment Level A minimum miscibility enrichment level option has been added to the multi-contact miscibility calculation. This feature allows calculation of the minimum fraction of rich gas required to be added to a lean gas stream to achieve multi-contact miscibility with an oil at a specified pressure. A minimum rich gas fraction and a number of gas fraction steps are specified. WinProp performs multiple-contact calculations for each step in the rich gas fraction, and interpolates to determine the minimum enrichment level for multi-contact miscibility. Results of the calculations for each solvent gas mixture tested are displayed on ternary diagrams. This feature is an addition to the existing multi-contact calculation for determination of the minimum miscibility pressure for a given oil and solvent. K-Value Plotting The phase property plotting feature has been enhanced to allow generation of K-value plots for the 2-phase flash, multiphase flash, and the STARS K-value calculation options. GasLiquid, Liquid-Liquid and Aqueous-Liquid K-value plots may be generated. The results are shown as the log of the K-value for each component, plotted against pressure, temperature or composition, depending on which independent variable has been specified for the flash. STARS Fluid Model Generation Enhancements The options for treatment of surface streams for STARS production reporting can now be specified in WinProp. This includes specifying the surface pressure and temperature, the flash options *SEGREGATED or *KVALUE and also the new option for specifying K-values which are used only for the surface flash. The ability to specify these K-values separately from the K-value tables allows the pressure and temperature range for the tables to be concentrated on the expected reservoir conditions, but still calculate accurate surface phase splits. Both Gas-Liquid and Liquid-Liquid K-values at the surface can be specified. The extrapolation algorithm for determining component K-values outside of the range of convergence of the flash calculations has also been improved.
New Features in WinProp 2001.10 Thermal Compositional Gradient Model Beginning with the 97.00 release, WinProp has had the capability to perform isothermal gravity/chemical equilibrium calculations for the determination of compositional grading due to gravity. The 2001.10 release includes the option to incorporate thermal effects on the gradient calculation. The model equations are developed based on the zero mass flux condition. Calculations may be performed without thermal diffusion (passive thermal gradient case) or with thermal diffusion coefficients determined from correlations or entered as constant values for each component.
6 • New Features
User's Guide WinProp
New Features in WinProp 2000.15 STARS PVT Data Generation Enhancements A number of features for creating STARS component property and K-value data have been added to WinProp. For component properties the following features have been implemented: optional use of WinProp’s viscosity model for component viscosities as opposed to the corresponding states model, optional output of viscosity versus temperature table instead of correlation coefficients, and the generation of viscosity and density nonlinear mixing functions. For K-value data, the features added include: generation of liquid-liquid and gasliquid K-value tables simultaneously, generation of composition dependent K-value tables, use of STARS defaults for water K-values, indication of which K-values have been extrapolated in the tables, and output of a map comparing the WinProp calculated phase split to that determined from the K-value tables. Please see the STARS PVT Data Generation section of the User’s Guide for more details. WinProp-ModelBuilder Integration Several features have been introduced to enhance the data flow between WinProp and ModelBuilder. The concept of PVT “Meta-Data” has been introduced; this refers to the equation of state model and mixture composition used to generate the PVT data for IMEX or STARS (for GEM, the equation of state model used is the same as in WinProp, so Meta-Data is not required). In this release of WinProp, the PVT Meta-Data will be written out to the file with the IMEX fluid model. When this file is imported into ModelBuilder, the Meta-Data will be read in and stored in the simulator data set. If it is desired at a later date to analyze or modify the PVT data in some way, WinProp can be launched from within ModelBuilder and the Meta-Data EOS description will be restored to WinProp. The GEM EOS model can also be sent to WinProp by launching from within ModelBuilder. In this case, compositions determined from the initial conditions section will be transferred to WinProp as well. Additional PVT Tables An alternate format for black oil PVT tables has been added to the existing options for creating various IMEX or extended black oil PVT tables. The alternate format includes writing of the PVT table in order from highest to lowest pressure, and writing out a table of multiplying factors for the undersaturated oil compressibilities and viscosities. Enhancements to the extrapolation methods for generating PVT properties above the original saturation pressure of the oil have also been implemented. Laboratory Experiment Enhancements The maximum number of separators which may be specified with the constant volume depletion experiment and also for the black oil PVT data generation option has been increased to 8. Liquid dropout for the constant composition and constant volume depletion experiments can now be specified as a percentage of the cell volume at the saturation pressure, or as a percentage of the cell volume at the current pressure step.
User's Guide WinProp
New Features • 7
Interface Enhancements The differential liberation and constant volume depletion experiment data entry forms have been redesigned to allow entry of pressure step data in row format, for improved compatibility with experimental PVT reports. Data for material balance and consistency check calculations is now entered on a separate table which is linked to the main table with the pressure information. Pasting of data to any grid which allows a variable number of rows has been modified to automatically increase the number of rows in the table if required to hold all of the data being input.
New Features in WinProp 2000.10 Automatic Generation of Quality Lines on Phase Diagrams A feature has been added to the 2-phase envelope calculation option to allow the user to select lines of constant mole or volume fraction to be calculated and displayed on the plot of the phase envelope. In addition the algorithm has been improved so that the initial guess for the starting point is generated internally. The user no longer needs to initialize phase envelope calculations with a flash or saturation pressure calculation or provide a good guess for the starting point directly. It should now be possible to generate a 2 phase pressure temperature envelope with default selections reliably. Additional PVT Tables For CMGL’s IMEX simulator, WinProp can now generate Gas-Water PVT tables. “Extended” Black Oil type PVT tables can be generated including the Rv data describing oil solubility in the vapor phase. These data are generated by simulating a constant volume depletion or a differential liberation laboratory experiment. Oil properties are obtained by material balance calculations or directly through EOS separator calculations. A number of methods are available for extrapolating individual curves beyond the original saturation pressure. These tables are output in a generic format. The user can then customize this data for use with specific extended black oil reservoir simulation programs. Additional Experimental Data The constant composition expansion experiment option has been enhanced to allow regression on the following experimental data: viscosity, density, compressibility factor and single phase oil compressibility. These data are included in the regression only when the corresponding property can be calculated by the program. For example single phase oil compressibility data will not be used in regression for a dew point fluid. Asphaltene Precipitation Modelling Case Study A new case study is included in the User’s Guide and on-line help which describes the development of a model for prediction of asphaltene precipitation from a black oil under pressure depletion. The case study illustrates characterization of the oil, regression to match fluid phase behavior data, specification of the asphaltene model parameters, and calibration of the model with experimental precipitation data. All of the case studies are now included in Appendix A. 8 • New Features
User's Guide WinProp
Interface Enhancements A feature has been added to allow calculation options to be temporarily excluded from the data set, rather than deleting them entirely. Options are excluded/included from the main control form by right-clicking on the desired row and making a selection from the pop-up menu. One application of this feature is to temporarily reduce the number of calculation options within a regression block to try and obtain a match to some key data. After an initial regression run, the component properties can be updated and calculation options that were excluded can be included again for further regression runs. Data entry and navigation on the grids has been improved by enabling use of the left and right arrow keys, in addition to the up, down and enter keys.
New Features in WinProp 1999.10 Enhancements to Aqueous Phase Solubility Calculations WinProp supports calculation of solubility of light gas and hydrocarbon components in the aqueous phase using Henry’s law. This feature is enabled by selecting flash type OGW (OilGas-Water) on the OGW/EOS Multiphase Flash form. Henry’s law constants can be entered by the user or calculated internally using correlations fit to experimental solubility data. Two new features have been added for modelling aqueous phase solubility. First, modification of the internally calculated Henry’s constants to account for salinity of the aqueous phase has been implemented. By default, the internal Henry’s constants are for pure water. To predict solubility of components in brine, all that is required is brine salinity, in terms of equivalent NaCl concentration. This is entered on tab Aqueous phase of the Components Selection/Properties form. The second feature implemented is regression on the aqueous solubility parameters to match experimental solubility data. Component reference Henry’s constants, i.e. Henry’s constant at a specified reference pressure, and molar volume at infinite dilution can be adjusted to match experimental data. Please see the “Components” section for further description of Henry’s constants. Case Study number two, in the “Tutorial” section, illustrates the use of both of these new features. Pedersen Viscosity Correlation WinProp now allows use of the Pedersen corresponding states viscosity correlation in addition to the Jossi-Stiel-Thodos (JST) correlation. The Pedersen correlation is expected to give better liquid viscosity predictions for light and medium gravity oils than the JST model. The Pedersen correlation is not dependent on having accurate density predictions as the JST technique is. Parameters in either correlation may be adjusted during regression to match experimental viscosity data. Please see the “Components” section for more information on viscosity models.
User's Guide WinProp
New Features • 9
Generation of PVT Properties for CMG’s IMEX Simulator WinProp can now generate the PVT data corresponding to the light oil and the pseudomiscible models of CMG’s IMEX simulator. Earlier releases targeted the black oil model only. In addition, the aqueous phase properties can now be estimated from built in correlations as an alternative to entering the values directly. The PVT fluid model data with the associated IMEX keywords is written to an output file with the extension (.imx). This file can be referenced as an include file in an IMEX data file. Please refer to the “IMEX PVT data generation” chapter of this manual for a complete discussion. Consistency Checks and Material Balance Calculations A number of tools are available in WinProp for evaluating the quality of PVT data provided to the reservoir engineer from laboratory or field measurements. The data is typically used to tune the EOS model. It is imperative therefore that the PVT data is analyzed critically prior to any detailed regression calculations. The tools available include Hoffman plots and material balance calculations. Material balance calculations for the constant volume depletion (CVD), differential liberation (DL) and separator options are performed if the required data is entered. For these experiments, the required data are generally reported in a typical PVT report from a laboratory. A Hoffman plot is generated for the recombination option based on the entered oil and gas compositions. Hoffman plots are also created with the CVD, DL and separator options if sufficient data is entered to calculate the oil phase compositions from a component material balance. Refer to the chapter on “Laboratory Calculations” for more detail as well as template cases matbal-bo.dat and matbal-gc.dat. Changes to the Multiple Contact Miscibility (MCM) Option A number of enhancements have been made to the MCM option with the objectives of 1) alleviating difficulties in interpreting the program results and 2) determining and reporting multiple and first contact miscibility pressures directly. With respect to point one, the criteria used for stopping the forward and backward contact flash calculations are reported in the output file. The most likely reasons are either miscibility is achieved or there is no change in the oil and gas compositions from the previous contact. With respect to point two, the user can now enter a range of pressures for the calculation. If multiple and/or first contact miscible pressure(s) are found in this pressure interval then these values are reported at the end of the output listing. Ternary diagrams are also automatically created at designated intervals. Specification of Mole Fraction Steps for Flash Calculations The ability to specify steps in the primary mole fraction making up the feed to a flash calculation has been implemented for two-phase, multiphase and asphaltene/wax flash calculations. This allows the specification of flashes for a number of mixtures of the primary and secondary compositions on a single flash form. This feature is similar to the existing capability for specifying pressure and temperature steps. These steps can be defined with the feed specification on the first tab of each flash calculation.
10 • New Features
User's Guide WinProp
Plotting Capability Added to Two-Phase and Multiphase Flash When a series of flash calculations have been specified by setting temperature, pressure or mole fraction steps, plots of the phase properties can be generated. Up to three phase properties, such as molecular weight, compressibility factor or phase mole fraction, can be selected for each flash calculation. One plot is generated for each property and each phase. When plotting is activated, steps can be specified in one or two of the variables: pressure, temperature and mole fraction. If steps are specified for only one variable, the plots are generated with that variable as the independent variable, and the phase property as the dependent variable. Up to 100 steps in the independent variable are allowed. When steps are specified for two variables, one variable is treated as a parameter variable, and curves of the phase property are displayed for each value of the parameter variable. Up to 8 steps in the parameter variable are allowed. The phase properties to be plotted are selected on tab Plot Control of the flash calculation forms. Plotting Capability Added to Asphaltene/Wax Flash The asphaltene/wax flash has a plotting feature similar to the one described above for the two-phase and multiphase flashes. This allows generation of plots such as weight % precipitate as a function of solvent concentration or pressure. A special plotting feature implemented for the asphaltene/wax flash is the generation of a pseudo-ternary diagram to display the results of flash calculations in terms of the predicted phase split, i.e. liquid-vapor, solid-liquid etc. The results are shown for a number of dilution lines defined by the user. Plot specification is done on tab Plot Control of the asphaltene/wax flash calculation. Three-Phase Envelope Automatic Plot Generation Automatic plot generation has been implemented for the three-phase boundary calculation. Excel plots can now be created for three-phase P-T, P-X and T-X diagrams. These plots can be created by selecting File|Create Excel plots after running a data set with a three-phase envelope calculation option. Ternary Diagram Two-Phase Envelope Generation The capability to create ternary or pseudo-ternary two-phase boundaries has been added to the two-phase envelope calculation option. This calculation locates points in composition space defining the two-phase vapor-liquid phase boundary on a triangular diagram. This can be considered a static or single-contact calculation, as opposed to the multiple contact calculation option which performs a dynamic simulation of multiple contact miscibility processes. This feature is enabled by selecting Pseudo-Ternary Phase Envelope on the Two-phase envelope calculation option form. Table Import Wizard A Table Import Wizard has been implemented in WinProp to assist the user in importing data into WinProp from existing Excel or ASCII format files. The wizard guides the user through the steps of selecting data to be imported, defining units and performing unit conversions, and inserting the imported data into the correct locations in WinProp’s data structure. Table import is available for the following forms: Component Selection/Properties, Plus Fraction Splitting, Constant User's Guide WinProp
New Features • 11
Composition Expansion, Differential Liberation, Constant Volume Depletion and Swelling Test. An example illustrating the use of the Table Import Wizard is given in the “Tutorial” section of the manual. Information regarding the specific implementation for the forms listed above may be found in the “Components”, “Component Splitting and Lumping”, and “Laboratory Calculations” sections. Interface Enhancements Two toolbars are provided for easier access to items previously available through the menus alone. The main toolbar contains buttons corresponding to items in the File and Edit menus. This toolbar targets frequently performed tasks such as opening and saving files, generating the results, viewing the output file and creating plots. This toolbar is not customizable and is permanently displayed. A second toolbar contains buttons corresponding to often used calculation options. These buttons are grouped to mirror the organization of the menus. This toolbar is customizable. The user can remove any of the buttons selected by default and add buttons corresponding to options not originally chosen. Once the toolbar is customized the settings are saved for subsequent sessions. The options toolbar can also be removed from the interface and reinstituted at a later time. The menu system is revised with the objective of creating more intuitive classes. Similarly, the names of the forms corresponding to the calculation options are modified to be more descriptive. Forms for the constant volume depletion, separator test and differential liberation are redesigned in light of the additional data that can now be entered for material balance calculations. Other enhancements include the addition of progress bars in specific situations. A progress bar is shown when loading or saving the component form for example.
New Features in WinProp 98.00 Additional Methods for Heavy Fraction Characterization The three-parameter gamma distribution is now available in WinProp to describe the molecular weight versus mole fraction relationship for the heavy fraction of a petroleum fluid. The Gaussian quadrature method is used in evaluating the integral of this distribution function. The molecular weight of the pseudo components selected corresponds to the quadrature points. Good VLE results are obtained with this method with a small number of pseudo components. In addition the Gamma distribution and Gaussian quadrature can be used to generate a single set of pseudo components for multiple related samples with different plus fraction molecular weight and specific gravity. Related mixtures have the same compounds but in varying proportions, for example saturated oil and its equilibrium gas or fluids from different depths in a reservoir with a compositional gradient. Parameters of the Gaussian distribution function are obtained by nonlinear regression if extended analysis data is entered or from generalized correlations if only plus fraction specific gravity and molecular weight are available. Where multiple samples are involved each sample can have extended analysis data entered if available. Please refer to the “Component Splitting and Lumping chapter of this manual for a more extensive discussion.
12 • New Features
User's Guide WinProp
Generation of PVT Properties for IMEX Black Oil Model WinProp can now generate the PVT data corresponding to the “black oil” model of CMG’s IMEX simulator. This data is written out to an output file with the extension blk. This file can then be referenced as an include file in an IMEX data file. The properties of the oil phase (formation volume factor, gas oil ratio) are generated by flashing the equilibrium liquid at each stage of the “differential liberation” directly through the user specified separator train. The range of the PVT table can be extended to include pressures above the original oil bubble point pressure by generating the swelling curve. This way the table can handle variable bubble point scenarios arising for example from gas injection or solution gas migration followed by repressurization. This option can be found under Options | "Black oil model PVT data." Please refer to the “Black oil PVT data generation chapter of this manual for a complete discussion. Process Flow and Isenthalpic Flash Options Data entry forms for the Process flow and Isenthalpic flash options have been added to WinProp. The process flow option can be added to the data file by selecting Calculations | Process flow from the menu and isenthalpic flash by selecting Calculations | Isenthalpic flash. For the process flow sample template are process1.dat, process2.dat and process3.dat. For isenthalpic flash the sample templates are isenth1.dat, isenth2.dat and isenth3.dat. Please refer to the chapter titled “Process flow” for detailed discussion of the process flow option and the “Flash calculations chapter for more details on the isenthalpic flash option. Support for Multiple Hydrocarbon-Hydrocarbon Binary Interaction Exponents Hydrocarbon components are identified by a value of 1 on the HC column of the component table on the Component form. Binary interaction coefficients between two hydrocarbon components are calculated from a correlation, which involves the critical volume of each component and an exponent parameter. In contrast to previous versions of WinProp where all HC-HC binaries were calculated based on a single exponent parameter, the user can now group pairs of binary and specify a different exponent parameter value for each group. These individual group exponents can be also selected as regression parameter(s). Please see the chapter entitles “Components and “Regression for more details. Handling of the “Regression Block” in a Data File In WinProp the regression block refers to the calculation options that are between the “Regression” and “Start regression” forms. For a case to run successfully all options in this block must have at least one piece of experimental data entered and all options outside the regression block are required not to have any experimental data entered. WinProp will now attempt to ensure that these requirements are met when the user attempts to run a given case while preserving the data that has been entered. For example if there an option within the regression block then this option will be moved out of the regression block. If there is an option with experimental data outside the regression block then the experimental data will be written out to the data file with the accompanying keyword(s) commented out. This will also allow the user to retain the experimental data that were entered for regression when regression is removed from the data file, that is “Regression” and “End regression” forms are removed. The entered experimental data will be shown where appropriate with the program predictions on plots even if there is no regression involved in the run.
User's Guide WinProp
New Features • 13
Interface Enhancements The list of the five most recently files accessed by WinProp is now available on the File menu. This is a faster way of selecting a case than through the file open dialog box. Interface enhancements include the ability to redirect the screen diary to an output file. To redirect select “Redirect to file DBPROP.XXX” under File | Screen menu. The user can now select an editor other than Notepad by invoking the Editor | “User editor select” option under the File menu. This will open a file dialog box. Using the file dialog select the executable file corresponding to the desired editor. WinProp allows up to open up to 8 different cases (data files) to be open simultaneously, primarily to allow various calculation option forms to be copied between different data files. This saves the user from having to type in data values multiple times. The MDI capability also facilitates comparing the data entered for a given form across data files. A number of checks have been implemented to avoid violating the internal design limitations of this option. For example forms can be opened only when a single case is loaded and a case cannot be closed until all the open forms are closed. In previous versions of WinProp the data in a table (grid) could be changed via a text box positioned outside the table. With WinProp 98.00 a floating text box positioned exactly on the desired cell is used for table (grid) edits. To erase the current value or text in a cell and enter a new value or text, position the cursor on that cell and start typing. To edit the contents of a cell, position the cursor on that cell and double click with the left mouse button. The cell contents are updated when the carriage return (Enter) key is pressed or if the cursor is moved to another cell. Please note that changing the focus to a new control will not update the grid (table) contents.
New Features in WinProp 97.00 Compositional Grading Calculations Significant compositional variation with depth can occur in deep reservoirs with near critical fluids or for fluids where there is a large variation in molecular weight between the light and heavy constituents. This effect is important in estimating materials in place as well as field development and operation strategy. WinProp now has the capability of simulating this phenomena based on the isothermal gravity/chemical equilibrium (GCE) formulation. This option can be found under Calculation Options|Compositional Gradient. A complete discussion can be found in the chapter titled Compositional Grading. Generation of PVT Properties for STARS STARS is CMG's steam and additive thermal simulator. WinProp can generate the complete PVT data required by STARS. This includes component partial densities, compressibility and thermal expansion factors as well as liquid component viscosity coefficients. WinProp can also generate tabular K-value data between any two phases that STARS supports. STARS used K-values to determine the number of phases in equilibrium and the composition of each phase. The PVT data is printed in a format suitable for direct inclusion in a STARS data file. The output of this option is directed to a file with a suffix .tbl. This option can be found under Options|Print STARS PVT Table. Please refer to the STARS PVT Data Generation chapter of this manual for a more extensive discussion.
14 • New Features
User's Guide WinProp
Regression Enhancements It is now possible to specify more than one component for a given property such as the critical pressure as a single variable in regression. The members of the group will in general have individual initial values and bounds. In regression the same increment is applied to all members of the group. This feature can be useful if it is desired to maintain a certain trend or symmetry for a given property or in avoiding regressing on a property belonging to a component with a small mole fraction. For information on how to define group variables refer to the Regression chapter of this manual. Summary plots showing before regression, after regression and experimental data are now generated automatically when Excel plots are created from a regression run. Individual plots showing calculated results are still available, with new titles indicating before or after regression calculations. Conversion from CMGPROP to WinProp Format A conversion utility is provided within WinProp to translate files created for CMGPROP on UNIX or PC platforms. This utility can be invoked by selecting Options|Convert from Cmgprop to WinProp. The user is advised to open each form and verify the results of the conversion carefully. Please use the Save As option under the File menu to save the WinProp compatible data file to avoid overwriting the original CMGPROP data file. The original file will be an important aid in case difficulties are encountered in conversion and in verifying the conversion. There are a number of situations that can pose difficulties for the converter including the use of wildcards in specifying array values and presence of comment marker on a line where array values are stipulated. Please edit the CMGPROP data file eliminating these situations prior to using the conversion utility. MDI Capability The Multiple Document Interface (MDI) Feature is now implemented in WinProp. This allows the user to open up to eight files at once. This has significant advantages for example when the user desires to compare output files for two or more cases or in the ease with which data corresponding to various calculation options may be copied between different data files. Refer to the section copying between different data files under the Tutorial chapter of this manual. Update Component Properties Feature Upon completing a splitting, lumping or regression calculation where the number of components are changed or the component properties modified, WinProp writes out the revised component information in an output file with the suffix .rls. With the previous version of WinProp the user would run a file, for example test1.dat with a splitting calculation, use File|Open to open test1.rls, use File|Save As to rename to test2.dat for example and then continue working with this file by appending calculation options to it. This procedure is now automated with the introduction of the update component properties selection under the Options menu. The user still runs the splitting calculation with test1.dat. Once the calculation is carried out, update component properties is invoked. This updates the information on the Composition and Component forms. The user then removes the splitting calculation from the data file and appends the desired calculation options. Optionally the user may wish to save this file with a different file name say test2.dat to retain a complete work record of the session.
User's Guide WinProp
New Features • 15
Addition of Bounds Tab on the Regression Form An additional tab showing the initial value and the lower and upper bound selected by WinProp for each regression variable specified has been added to the Regression form. The user may subsequently edit the bounds. The capability to restore values back to their default selections is provided as well. This provides the user greater flexibility in arriving at an EOS description based on the specific characteristics of the fluid being considered and the PVT data available. Volume Shift Specification Additional flexibility is introduced in selecting values for the volume shift parameter for each component. Previously the default was a value of zero for all components. The new default is a value generated from the correlation for library components and a value of zero for user defined components. The user may apply the correlation values to all components by selecting Reset to Correlation Values from the Volume Shift menu on the component form. Alternatively the user may revert to the older default by selecting Reset to Zeros. The user can still specify a value for any component which is different from either correlation or zero by editing the cell directly. Support of Two Sets of EOS Parameters WinProp now supports the concept of two different EOS models. When two sets are enabled the first set is used for calculations at reservoir conditions and the second set for surface or separator conditions. With this provision it is possible to match PVT experimental data at surface conditions (typically separator API and GOR data) independently from data at reservoir conditions. This makes it possible to obtain much more accurate predictions over the wide range of conditions encountered as the fluid is produced and processed on the surface with a realistic number of components for compositional simulation. Please refer to the Component and Regression chapters for details. Extended Separator Option The conventional separator operation involves the liquid phase output from a given separator becoming the feed for the next separator in sequence downstream and the vapor phase joining the gas product stream. This arrangement is not always optimal particularly for rich gas condensates. For modeling alternative separation strategies the separator option is enhanced to allow additional product streams such as LPG and in providing flexibility in the selection of the destination of the liquid and vapor stream from each separator. Please review the section on separator calculation in chapter Laboratory Calculations for more information of this feature. Multicomponent Solid Precipitation Model The solid precipitation model is now suitable for modeling both wax and asphaltene precipitation scenarios. The thermodynamic model has been enhanced as follows: the precipitate is now modeled as a multicomponent solid in contrast to the earlier single component pure solid phase assumption, non-isothermal conditions are treated, and up to three fluid phases in equilibrium with the solid are allowed.
16 • New Features
User's Guide WinProp
Introduction
What is WinProp? Welcome to WinProp, the Windows version of CMGPROP. WinProp is CMG's equation of state multiphase equilibrium property package featuring fluid characterization, lumping of components, matching of laboratory data through regression, simulation of multiple contact processes, phase diagram construction, solids precipitation, and more. Laboratory experiments considered in WinProp include recombination of separator oil and gas, compressibility measurements, constant composition expansion, differential liberation, separator test, constant volume depletion and swelling test. You can use WinProp to analyze the phase behavior of reservoir gas and oil systems, and to generate component properties for CMG's compositional simulator GEM, black oil simulator IMEX and steam and additives thermal simulator STARS. WinProp contains a graphical interface that allows you to prepare data, run the phase property calculation engine, view the output with an editor, and create plots with Excel™. WinProp creates keyword data files to drive the phase behavior calculation engine. Besides the regular keywords that were required by the CMGPROP program, these data files contain special control character strings for the graphical interface. A conversion utility is provided within WinProp for users who have been using CMGPROP on a UNIX platform or on the PC to facilitate the migration to WinProp.
User's Guide WinProp
Introduction • 17
Use of this Manual This User's Guide describes the different forms and options for entering data into WinProp. It is also available as on-line help. This User's Guide is aimed at reservoir engineers with some background knowledge on the phase behavior and characterization of reservoir fluids. Good references on these topics can be found in Ahmed [1], Pedersen, Fredenslund, and Thomassen [30] and McCain [17] (see the “References” section). For more details on phase equilibrium thermodynamics, please see Sandler [35] or Walas [37]. Every attempt has been made in the preparation of this User's Guide to provide you with all of the information necessary to run the program and understand the calculations being performed. If questions arise, please contact: Computer Modelling Group Ltd. #150, 3553 – 31 Street N.W. Calgary, Canada T2L 2K7 Telephone: (403) 531-1300 Fax: (403) 289-8502 Email:
[email protected] Website: www.cmgl.ca
Installation All CMG software must be installed from the CD-ROM by running the Setup program. Please refer to the detailed installation instructions that are packaged with the software for additional information.
Confidentiality All components of CMG's technology including software and related documentation are protected by copyright, trademark and secrecy. CMG technology can be used only as permitted by your license from CMG. By the license, you have agreed to keep all CMG technology confidential and not disclose it to any third party. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic, mechanical, or otherwise, including photocopying, recording, or by any information storage/retrieval system, to any party other than the licensee, without the written permission of Computer Modelling Group Ltd.
18 • Introduction
User's Guide WinProp
Template Data Files A number of example data files are located in the "TPL" directory located under the WinProp directory. A brief description of each of the available template data files is shown below: Data file name Description AqueousCO2-08-Harvey.dat Aqueous phase properties calculation using Harvey’s method case_study-1.dat Data for case study number 1 (See Appendix A) case_study-2.dat Data for case study number 2 (See Appendix A) case_study-3-asph.dat Data for case study number 3 (See Appendix A) case_study-3-regress.dat Data for case study number 3 (See Appendix A) case_study-3-split.dat Data for case study number 3 (See Appendix A) cce.dat Constant composition expansion calculation compgrad-blackoil.dat Compositional gradient calculation - black oil compgrad-voloil.dat Compositional gradient calculation - volatile oil compress.dat Single-phase liquid compressibility calculation cricon.dat Cricondenbar and cricondentherm calculation critical.dat Critical point calculation cvd.dat Constant volume depletion simulation diflib.dat Differential liberation experiment simulation envel_2ph-pt.dat Two-phase pressure-temperature envelope construction envel_2ph-px.dat Two-phase pressure-composition envelope construction envel_2ph-tern.dat Two-phase pseudo-ternary diagram construction envel_3ph-pt.dat Three-phase pressure-temperature envelope construction envel_3ph-px.dat Three-phase pressure-composition envelope construction extended_blackoil.dat Extended black oil PVT tables with oil vaporization flash-2ph.dat Two-phase EOS flash calculation flash-3ph.dat Three-phase EOS flash calculation flash-isenth1.dat Isenthalpic flash - 2 component system flash-isenth2.dat Isenthalpic flash - 6 component system flash-isenth3.dat Isenthalpic flash - single component system flash-ogw.dat Three-phase oil-gas-water Henry's law flash calculation format2_blackoil.dat Alternate format black oil PVT tables imex_condensate.dat IMEX gas-water with condensate PVT model data generation imex_voloil.dat IMEX volatile oil PVT model data generation imex-blackoil.dat IMEX PVT model data generation labpvt-bo1.dat Lab PVT experiment simulations – black oil no. 1 labpvt-bo2.dat Lab PVT experiment simulations – black oil no. 2 labpvt-bo3.dat Lab PVT experiment simulations – black oil no. 3 labpvt-gc1.dat Lab PVT experiment simulations – gas condensate no. 1 labpvt-gc2.dat Lab PVT experiment simulations – gas condensate no. 2 labpvt-gc3.dat Lab PVT experiment simulations – gas condensate no. 3 lumping.dat Lumping "plus fraction" components matbal-bo.dat Material balance checks for black oil PVT experiments matbal-gc.dat Material balance checks for condensate PVT experiments User's Guide WinProp
Introduction • 19
mcm-condensing.dat mcm-vaporizing-co2.dat mcm-combined-H95-8lean.dat mcm-combined-U2002rich.dat mcm-Z12-5-MME.dat process-cvd.dat process-mcm.dat process-plant.dat recombine.dat regress-blackoil1.dat regress-blackoil2.dat regress-compress.dat regress-condensate1.dat regress-condensate2.dat regress-critical.dat regress-flash_2ph.dat regress-flash_3ph.dat regress-flash_ogw.dat regress-lightoil.dat regress-multicontact.dat regress-sat_pres.dat regress-separator.dat regress-singlephase.dat regress-viscosity.dat sat-pressure.dat sat-temperature.dat separator.dat singlephase.dat solid-asph_plots.dat solid-asph1.dat solid-asph2.dat solid-phenanthrene.dat solid-wax.dat split-mw_analysis.dat split-mwsg_analysis.dat split-mwsg_plus.dat split-mwsgtb_analysis.dat stars-comp_props.dat stars-vl_kvalues.dat stars-vlaq_kvalues.dat stars-vls_kvalues.dat swelling.dat
20 • Introduction
Condensing gas drive multicontact miscibility calculation Vaporizing CO2 drive multicontact miscibility calculation Condensing and vaporizing combined drive MMP calculation Condensing and vaporizing combined drive MMP calculation Condensing and vaporizing combined drive MME calculation Process flow – simulation of constant volume depletion test Process flow – simulation of multiple contact experiment Process flow – simulation of a gas plant Recombination of separator oil and gas streams Black oil no. 1 regression Black oil no. 2 regression Liquid compressibility regression Gas condensate no. 1 regression Gas condensate no. 2 regression Critical point regression Two-phase flash regression Three-phase EOS flash regression Three-phase Henry's law flash regression Light oil regression Multiple contact data regression Saturation pressure regression Separator data matching with 2nd EOS set parameters Single phase properties regression Regression for viscosity matching Saturation pressure calculation Saturation temperature calculation Separator calculation Single-phase fluid properties calculation Plot construction for single component asphaltene model Single component solid asphaltene precipitation Heavy oil with 2 component solid precipitation Pure component solid (phenanthrene) precipitation Multicomponent wax precipitation Characterization - MW versus mole fraction data Characterization - MW, SG versus mole fraction data Characterization – plus fraction MW and SG only Characterization - MW, SG ,TB versus mole fraction data Component PVT properties generation for STARS Vapor -Liquid K-values generation for STARS Vapor -Liquid-aqueous K-values generation for STARS Vapor -Liquid-solid K-values generation for STARS Swelling experiment simulation
User's Guide WinProp
Tutorial Section
Overview This chapter includes information on the mechanics of creating, editing, saving and running data sets in WinProp, as well as viewing the output files and creating plots. Example case studies with step-by-step instructions for performing some PVT modelling tasks are described in Appendix A. Detailed instructions for using all of the calculation options available in WinProp are given in the remaining chapters.
Getting On-Line Help Selection of Help on the menu provides you with the following options: Contents Search for Help on... Help on current form
The table of contents for the help file is displayed You can search for help on a particular topic The help on the current form is displayed
The help on current form can be also invoked by pressing the function key F1
Creating, Opening and Saving Data Files You can create a new data file by selecting File|New from the menu. WinProp puts three undefined forms in the data set: Titles/EOS/Units, Component Specification/Properties, and Composition. An existing data file can be opened by selecting File|Open.... A file browser will appear to assist you in the file selection. You save a data file by selecting File|Save. A data file can be saved under a different file name by selecting File|Save As.... By convention all data set names have the (.DAT) suffix. The following files are created when running WinProp:
User's Guide WinProp
Tutorial Section • 21
File suffix
Description
.out
ASCII file containing calculation results.
.gem
Output of component properties in a format suitable for the compositional simulator GEM.
.gmz
Output of composition versus depth data in format suitable for inclusion within the GEM simulator data file.
.str
Output of PVT data in format suitable for inclusion within STARS simulator data file.
.imx
Output of the “black oil”, “light oil” or “pseudo-miscible” model PVT data in format suitable for inclusion within the IMEX simulator data file or extended black oil tables in a “generic” format.
.rls
Output of component properties from the regression or lumping and splitting procedure.
.srf
Output for plotting.
.xls
Excel™ file containing data and plots that are created from an .srf file.
The results are written to files with the (.out) suffix. When you invoke the regression or lumping or splitting procedures, WinProp also creates a file with the suffix (.rls.) This file can be opened to create a new data set (see Chapters on “Component splitting and lumping” and “Regression”). If you select the component printing option for CMG’s compositional simulator GEM on the form CMG GEM EOS Model, the component properties are printed to a file with the suffix (.gem) in a format suitable for GEM. If the CMG STARS PVT Data option is selected then an output file with the suffix (.str) is created. If the “Write GEM *ZDEPTH …” checkbox on the Compositional Gradient form is checked off then the composition versus depth information is written out to a file with the suffix (.gmz.). If the calculation option to generate PVT data for simulation studies with IMEX is included in the data set then a file with the suffix (.imx) is created. This file contains PVT data in a format compatible with IMEX and can be referenced as an include file in an IMEX data file. Select File|Exit to exit WinProp.
Running, Viewing Output and Creating Plots To run the current data set, select File|Run from the menu (or use F2 key). The results of the calculations are in a (.out) ASCII file. To view this file with an ASCII text editor, select File|View output (or use F3 key). The default editor for output viewing is Windows Notepad. The option is also available to use another editor of your choice. You can specify which editor to use by selecting Preferences|Editor|User editor select from the menu. This will open a file dialog box. The desired editor is selecting by identifying the executable file for that editor.
22 • Tutorial Section
User's Guide WinProp
Certain calculation options will create data for plotting. The plot information is in the (.srf) file. To create these plots with Excel™, select File|Create Excel plots (or type F4). WinProp has its own Excel™ templates and macros to invoke Excel™ and generate the corresponding plots. These Excel™ plots are saved in an (.xls) file. If no plot data are available, a message will be issued. To view an Excel™ plot that you have already created with WinProp, select File|View Excel plots.
Copying Between Different Data Files With the MDI implementation of WinProp the user may open as many as eight data files or associated files (such as the output file) for side by side comparisons or to transfer data between data files. To transfer calculation options between data sets: open the source and target files, highlight the desired rows on the data set structure form of the source file and select Copy from the Edit menu or by pressing the Ctrl C key combination. Next, click on the row of the data set structure form of the target file to select the insertion location and select Paste from the Edit menu or type the Ctrl V key combination.
Setting Up a Regression Run Certain calculation options including the simulation of laboratory PVT experiments allow the user to optionally enter experimental data which can be used to tune the EOS model. The Regression Parameters and End Regression forms bracket the calculation options for which data is entered. Note: All options that appear within the regression section must have at least one experimental data point. The Regression Parameters form is used to select the specific EOS component properties for tuning. For calculation options specified prior to the appearance of the Regression Parameters form the program uses the original component properties. For options appended after the End Regression form the component properties modified during regression are used. Note: WinProp only allows one Regression Parameters and one End Regression form per data set. To perform a second regression calculation first use the Update component properties feature located under the File menu.
Using the Update Component Properties Feature of WinProp Quite often the user is in possession of limited information on the composition of the reservoir fluid. This typically means a breakdown from C1 to C5 with the heavy end lumped as C6+ for which only the molecular weight and specific gravity information is available. In order to obtain reasonably accurate results with an EOS the heavy end must be described by more than one pseudo-component. This step is known as characterization or splitting. Since this procedure requires approximating a continuous distribution with a number of discrete components with limited experimental data for the heavy end, the pseudo-components properties are considered to be approximate and therefore suitable candidates for tuning to match available PVT experimental data. The splitting - regression sequence needs to be done in two steps since prior to the splitting calculation the pseudo-components do not exist to enable various properties such Pc or Tc to be selected for regression. The execution of this two step process can be done efficiently with the help of the Update component properties feature of WinProp. The process generally involves the following sequence: User's Guide WinProp
Tutorial Section • 23
1. Set up the splitting calculation. Add the form for performing the splitting calculation to the WinProp data file. Open the Component Selection/Properties form. The compositional analysis up to C5 involves components with known properties. Add these components by selecting Add Component|LibraryComponent. Open the Composition form and enter the mole fractions as they appear on the laboratory report. Ignore the warning message about the sum not being equal to one. Open the Plus Fraction Splitting form and enter data for the plus fraction. 2. Run WinProp with the data file from step 1. Once the splitting calculation is performed WinProp writes out the full set of component properties including data for the pseudo-components in a special output file with the suffix (.rls). Open the File menu and select Update component properties option. WinProp will then read the (.rls) file and update the Composition and Component Selection/Properties forms based on the data in this file. 3. Remove the splitting form from the data set by highlighting the splitting calculation row on the data set structure form and selecting Edit|Cut from the menu. Proceed to set up the regression run as described in the section “Setting up a regression run”.
View the Keyword Data File Created by WinProp Under the File menu item, selecting View data for current option loads the keywords corresponding to a given calculation option (or form) in a text window, while the entire keyword file can be viewed by selecting View data set. This can be a useful aid in troubleshooting if the results are unexpected or there is difficulty running the program.
Selecting a User-Defined Editor Under the Preferences|Editor menu item, there are two choices for selecting the device used for viewing WinProp output: Windows notepad and a user defined editor. The default device for the user defined editor is the "DOS EDIT" program. To set this to another editor of your choice, choose the Select user editor option under Preferences|Editor. This will bring up a file dialog box. Browse to the folder where the executable file for the desired editor is located. Select the executable file (typically with extension (.exe) or .(com)) for the preferred editor. The selection made will be honored until a new choice is made.
Editing the Data Set Editing Data Set Structure In addition to inserting calculation options as described in the Section “Data Set Structure”, you can edit the data set by selecting Edit from the menu. The edit operations will apply to the calculation options that are currently highlighted. The following menu items are available:
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This will undo the previous edit function. This menu item is not available if there is nothing to undo. This option will cut the options and the data associated with them into the Clipboard. You cannot cut the Titles/EOS/Units or the Component Selection/Properties forms. This option will copy the options and the data associated with them into the Clipboard. This option will paste the data from the Clipboard into the current data set.
Undo Cut
Copy Paste
You can use the Copy and Paste option to transfer information and calculation options within one WinProp data set or from one data set to another. Editing Tables On many forms, you enter data into tables (or grids). For most tables, you can use the menu item Table to insert a new row or delete rows. You can highlight the data in different cells with the left mouse button. You can delete, cut and paste data corresponding to the highlighted cells with the standard Windows keystrokes: DELETE for delete, CTRL+C for copy, CTRL+X for cut, and CTRL+V for paste. Note that DELETE clears the data in cells, but does not delete the corresponding rows. Please use Table|Delete rows if you want to delete rows.
Table Import Wizard Overview The Table Import Wizard is designed to assist the user in importing data such as component properties and laboratory experiment results into WinProp. The wizard is available for the following forms: Component Selection/Properties, Plus Fraction Splitting, Constant Composition Expansion, Differential Liberation, Constant Volume Depletion and Swelling Test. An example is given below illustrating the use of the Table Import Wizard. Information regarding the specific implementation for the forms listed above may be found in the “Components”, “Component Splitting and Lumping” and “Laboratory Calculations” sections of the manual. The wizard supports the following features: 1. Tabular information can be directly imported from Excel™ spreadsheets or ASCII format files. 2. Entire tables need not be imported. Parts of a spreadsheet/file can be extracted and imported into WinProp. 3. The regions being imported from the original table need not be contiguous. 4. The table imported into WinProp can be saved as a new file. 5. There is no restriction that the table being imported from has the same column arrangement as required in WinProp.
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6. Unit conversions can be performed on the table before importing it into WinProp. Unit systems can be selected for the entire table. Units can also be selected for individual columns.
Using the Table Import Wizard The Table Import Wizard guides the user through the steps required to import data into WinProp. The wizard is launched by clicking on a command button labeled Table Import Wizard on the forms mentioned in the overview. An example illustrating the import of component property data from an Excel™ file is shown here. Step 1: Provide file for table import from In this step the file which contains the table to be imported is identified. This file could be an Excel™ spreadsheet or an ASCII file. Indicate the desired file type by clicking on one of the option buttons labeled ASCII or Excel. Click on the Browse... button to locate the file.
Click on Next to continue. Step 2: Choose a worksheet This step appears as step 2 if an Excel spreadsheet was selected in Step1. Since a spreadsheet can have several worksheets, this step requires the identification of the worksheet that contains the data to be imported. The worksheets are listed in a list box at the top right corner. Once a worksheet is highlighted, data from that worksheet is displayed as in the example below.
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Click on Next to continue. Step 4: Select regions to be imported and define column names Step 3 is relevant only when importing from ASCII files and is skipped since this example involves importing from a spreadsheet. In step 4, the regions from the original table to be imported are identified and names are defined for all imported columns. Multiple ranges of columns can be selected, but a common set of rows must be selected for all columns. Before selecting the data, the table rows and columns can be transposed. If your data is in row-wise format, it can be transposed to allow definition of data types by column, as required by the table import wizard. Column names are selected by clicking on the right mouse button at the column header. This brings up a pop-up menu containing the available column names. Select the name that corresponds to the column from the menu. In the view of Step 4 shown below, the data corresponding to all columns except the Watson K-factor has been selected, and the column names defined.
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Click Next to continue. Step 5: Review table definition and edit data Step 5 can be used to review the table selections and edit values in the table before going on to select the units for the columns. The table can be inverted by clicking the right mouse button on the table and selecting Invert table from the pop-up menu that appears. The component table now appears as follows:
Click Next to continue.
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Step 6: Choose units of table columns In this step, the units used in the source table need to be identified. A base unit system is defined first. Units can then be set for individual columns as required by right-clicking on the column header and selecting the unit for that column from the pop-up menu. The units corresponding to the critical properties for this example have been selected as shown below.
It is important to note that selection of units in this step should correspond to the units used in the original file from which the table is being imported. No unit conversion is done at this stage. At this point, the table import may be completed by clicking on the Finish button. Any conversions to the current WinProp unit system will be performed and the data will be entered into the WinProp table. To view the table with quantities converted to different units or to save the table to a file, check on the box labeled Apply unit conversion and click Next to continue. Step 7: Choose units for table columns to convert data to In this step, the user has a choice of viewing the table with different units applied. Note that changing the units in this step does not affect what units will be used to display the data in WinProp. The table can also be saved to a separate file by clicking on the button labeled Save converted table to NEW file. In this example, the table from the previous step is shown after conversion to field units.
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Click Finish to exit Table Import Wizard and complete the import of data into WinProp.
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Data Set Structure
Overview
This form contains the structure of the data set. This is the first form presented to the user when WinProp is invoked. The column of the table labeled Forms contains the title for each calculation form included in the data set. By default the required forms Titles/EOS/Units, and Component Selection/Properties are pre-selected and cannot be removed. The Composition form is also required following these forms, thus it is included by default as well. The data entry form corresponding to a given row can be activated by double clicking on that row. Data can be entered and edited on each form. To insert a calculation option: (1) select the row where the new calculation will be inserted by clicking on that row; (2) select a calculation option from the menu or by clicking one of the buttons on the calculation option toolbar. The Inc (Included) column indicates whether or not a calculation option will be executed when the data set is run. A checkmark in this column indicates that the option will be included, while an X-mark indicates that the calculation will be excluded. Calculations can be included/excluded by right-clicking on the desired row and selecting Include Calculation or Exclude Calculation from the pop-up menu.
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A “U” in the Stat (Status) column indicates that the data for the corresponding option are undefined. Once data for a particular form are entered as described above, the “U” will be cleared from the status column. The text in the Comments column comes from the Comments text box on each form. These comments are also printed in the output file for each calculation option.
Editing Data Set Editing Data Set Structure In addition to inserting calculation options as described in the Section “Data Set Structure”, you can edit the data set by selecting Edit from the menu. The menu items apply to the calculation options that are highlighted. The following menu items are available: Undo Cut
Copy Paste
This will undo the previous edit function. This menu item is not available if there is nothing to undo. This option will cut the options and the data associated with them into the Clipboard. You cannot cut the Titles/EOS/Units or the Component Selection/Properties forms. This option will copy the options and the data associated with them into the Clipboard. This option will paste the data from the Clipboard into the current data set.
You can use the Copy and Paste option to transfer information and calculation options within one WinProp data set or from one data set to another.
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Titles/EOS/Units Selection
Overview This form is pre-selected by WinProp and appears as the first form in all WinProp data files. It is used for documenting the run, selecting the unit system and for choosing the equation of state (EOS) to be used for all calculations included in the data file.
Data Input Comments Enter your comments regarding this data set. These comments will be shown in the Data set structure form.
Title 1, Title 2, Title 3 Enter up to 3 titles to identify the runs.
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Titles/EOS/Units Selection • 33
Equation of State Selection of the equation of state for the oil and gas phases. The default is PR (1978). PR(1978) PR(1976) SRK(G&D) SRK
Peng-Robinson equation of state with 1978 expression for constant "a". Peng-Robinson equation of state with 1976 expression for constant "a". This is the original equation of state. Soave-Redlich-Kwong equation of state with the constant "a" proposed by Graboski and Daubert[6]. Original Soave-Redlich-Kwong equation of state.
Units psia & deg F kPa & deg C
Pressures in psia and temperatures in ºF. Pressures in kPa and temperatures in ºC.
kg/cm2 & deg C
Pressures in kg/cm2 and temperatures in ºC.
Mole
The feed on Form Composition is in moles, mole fractions, or mole percent. The feed on Form Composition is in mass (e.g. kg), mass fractions, or mass percent.
Feed
Mass
When the Mass option is selected, WinProp converts all mass fractions to mole fractions using the component molecular weights. All outputs will contain the corresponding mole fractions and not the input mass fractions.
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Components
Component Selection and Definition The equation of state requires the following properties for each component critical pressure (Pc), critical temperature (Tc), acentric factor (ω), and interaction coefficients between different components (δij). The molecular weight is also required to calculate mass densities. Additional factors such as the volume shifts τ, and the parameters Ωa and Ωb can also be defined for each component to enhance the equation of state predictions. A complete description for all of the properties in the component table is given in the "Component properties" section of this chapter. To select or edit components, double click on the row Component Selection/Properties of the data set structure form. This will bring up the Component Selection/Properties form. You can select components from WinProp’s component library or define your own components as described below.
Library Components To choose library components, select Options|Insert library components from the menu. The following form will be activated:
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Components • 35
Select components from the list by clicking on them with the left mouse button. Use the and keys for multiple selections. Pure hydrocarbon components, light gases and water may be selected from the library, as well as generalized single carbon number (SCN) petroleum fractions FC6 through FC45. The specific gravities, molecular weights and boiling points of the SCN fractions are taken from Whitson (1983). The critical properties of these fractions are calculated with the Lee-Kesler correlations (Kesler and Lee, (1976)). The component molecular weights are shown in brackets for each component primarily to allow the user to select generalized SCN fractions to approximate a heavy end of known molecular weight. The order in which components are selected depends on the sequence of mouse clicks. Click on View selection order to view this order. The component order is important for lumping into pseudo-components, as only components that are adjacent to one another can be lumped together.
User Component with Known Properties If you have a component with known critical properties, you can insert this component by choosing Options|Insert own component|Critical properties. This will activate the following form:
The critical pressure, critical temperature, acentric factor and molecular weight are required input. Values will be estimated for any of the OPTIONAL DATA parameter fields that are left blank. Critical compressibility is used only to calculate critical volume. Critical volume is used in the calculation of binary interaction parameters (see the section on “Interaction Coefficients” below). Specific gravity and boiling point temperature are used to estimate ideal gas enthalpy coefficients. Specific gravity is also used along with the critical properties to estimate Rackett’s compressibility factor, which is employed in calculating temperature dependent volume shifts. 36 • Components
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User Component with Known SG, Tb and MW For many heavy hydrocarbon fractions, the measured properties are specific gravity (SG), normal boiling point (Tb), and molecular weight (MW). These components can be defined by choosing Options|Insert own component|SG, TB and MW. The following form will be presented:
A minimum of two of the three properties must be entered. If one of the properties is not entered, it will be estimated using the selected Physical Properties Correlation. Note that critical properties are calculated from specific gravity and normal boiling point; molecular weight is used for determination of mass densities only. Thus if you enter SG and Tb, the critical properties will be unaffected by the choice of Physical Properties Correlation. The stated ranges of accuracy for the correlations are as follows. Twu: Tb up to 715 °C and SG up to 1.436 (Twu, 1984). Goossens: MW from 76 to 1685 (C120), Density from 0.63 to 1.08 g/cc and Tb from 33 to 740 °C (Goossens, 1996). Riazi-Daubert: Tb up to 455 °C and MW from 70 to 300 (Riazi and Daubert, 1980). For petroleum fractions up to about C20, all three correlations give similar results. For heavier fractions, the Riazi-Daubert correlation shows larger errors than the other two. The Goossens correlation gives very good predictions of MW from the other properties for alkanes up to C120. It should be noted that the form of this correlation limits boiling points to a maximum of 805 °C, regardless of the molecular weight and specific gravity. Once the physical properties are known, the critical constants for the component are determined using the selected Critical Properties Correlation. The ranges of applicability of the Twu and Riazi-Daubert correlations are as given above. The Lee-Kesler correlation was developed for Tb up to 650 °C, but is internally consistent for extrapolation above this temperature (Kesler and Lee, 1976). For acentric factors, the Lee-Kesler correlation is recommended for petroleum fractions. User's Guide WinProp
Components • 37
Component Properties After components have been selected or defined, their parameters and properties are shown on the form Component Selection/Properties. A typical example is illustrated below.
This form contains several tabs. The properties shown on Tab Component are listed in the table below. Additional explanation regarding some of the parameters is given in the notes following the table. Use of the temperature dependent volume shift feature is described under “Rackett’s compressibility factor” in the notes. Heading
Parameter or property
Component HC Pc(atm) Tc (K) Acentric fact. Mol. weight Vol. shift Z (Rackett) Vc (l/mol) Vc (viscosity) Omega A Omega B SG
Component name (maximum 8 characters) Hydrocarbon flag (=1 for hydrocarbons) Critical pressure in atm Critical temperature in K Acentric factor Molecular weight Volume translation (dimensionless) Rackett’s compressibility factor Critical volume in l/mol Critical volume in l/mol for viscosity calculations Ωa EOS parameter Ωb EOS parameter Specific gravity (water = 1)
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Tb (deg F | deg C) Parachor Ref. Henry (atm) V inf. (l/mol) P ref. (atm) Enth. Coeff. A Enth. Coeff. B Enth. Coeff. C Enth. Coeff. D Enth. Coeff. E Enth. Coeff. F Heating Value
Normal boiling point in °F (field units) or °C (SI units) Parachor IFT parameter Reference Henry’s constant in atm Molar volume at infinite dilution Reference pressure for Henry’s constant in atm Ideal gas enthalpy coefficient A (for units see note below) Ideal gas enthalpy coefficient B (for units see note below) Ideal gas enthalpy coefficient C (for units see note below) Ideal gas enthalpy coefficient D (for units see note below) Ideal gas enthalpy coefficient E (for units see note below) Ideal gas enthalpy coefficient F (for units see note below) Heating value (for units see note below)
Notes on Component Properties Hydrocarbon (HC) Flag: Binary interaction parameters between components with HC flags set to 1 are calculated via a correlation as described in the section on “Interaction coefficients” below. The interaction parameters between all other pairs of components may be set individually. Thus, if you wish to set individual interaction parameters between one component and all others, change the value of the HC flag for that component to 0. Note that the HC flags for CO2 and H2S have special values and should not be changed.
Volume Shift: The volume translation technique of Peneloux et al. (1982) is available for improving the prediction of phase density with the equation of state. Volume shift parameters are set to zero by default. The correlation of Jhaveri and Youngren (1988) can be applied to calculate volume shift parameters for all components by selecting VolumeShift|Reset to correlation values from the menu. To remove volume translation for all components select VolumeShift|Reset to zeros. Temperature dependent volume shifts can also be used by selecting the check box above the component table. The calculation of temperature dependent volume shifts is described next under “Rackett’s compressibility factor”. When printing component properties to the output file or for export to the GEM simulator, the most recently used volume shift values will be output.
Rackett’s Compressibility Factor (ZRA): Temperature dependent volume shifts are implemented using a technique similar to that described by Kokal and Sayegh (1990). Component volume shifts are evaluated at any temperature by taking the difference between the saturated liquid molar volume of a pure component calculated from the equation of state and the saturated liquid molar volume calculated using a modified Rackett equation: 1+ (1−Tr ) v s = ( RTc / Pc ) Z [RA
2/7
]
Rackett’s compressibility factors are available for all library components. For pseudocomponents, Rackett’s compressibility factors are back calculated from the critical properties and specific gravity using the assumption that the specific gravity is approximately equal to the saturated liquid density at 60 °F.
Critical Volume: Critical volumes are used only in the calculation of hydrocarbonhydrocarbon binary interaction parameters as described below under “Interaction coefficients”.
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Critical Volume for Viscosity: Critical volumes are used in the Jossi, Stiel and Thodos viscosity correlation (Reid et al., 1977) as described in this chapter under “Viscosity parameters.” These critical volume values are used only for the calculation of viscosity, and thus may be modified via regression to match experimental viscosity data without affecting the calculation of any other properties. Omega A and Omega B: The default values for Ωa and Ωb for the Peng-Robinson equation of state are 0.45723553 and 0.077796074 respectively. For the Soave-Redlich-Kwong equation of state, these values are 0.4274802 and 0.08664035 respectively.
Specific Gravity and Normal Boiling Point: Specific gravity is defined as the liquid density of the component at 60 °F and 1 atm divided by the density of water at 60 °F and 1 atm. For components with normal boiling points below 60 °F, the liquid density is taken as the saturated liquid density at 60 °F. If SG and Tb have been used to calculate critical properties and acentric factors, changing SG and Tb in the table will not affect the other properties. If you wish to recalculate the properties of a particular component with revised values for SG and Tb, please delete that component from the table using Options|Delete component, and insert a new component with revised values for SG and Tb, using Options|Insert own component|SG, TB and MW.
Parachor: The parachor value is used for calculating interfacial tension. Parachors are available for all of the library components. For pseudo-components and user components, parachors are estimated based on molecular weight using a correlation proposed by Firoozabadi et al. (1988).
Reference Henry’s Constant, Molar Volume at Infinite Dilution and Reference Pressure: These properties are used in calculating the solubility of components in the aqueous phase. There are three methods available for specifying these parameters: (1) Entering nonzero values for these properties in the component table, (2) entering zero values in the component table to allow internal estimation of Henry’s constants, (3) entering zero values in the table, but overriding the internal Henry’s constants with user input values entered for individual flash calculations. If nonzero values for the solubility parameters are entered in the component table, Henry’s constants are calculated from:
ln H i = ln H io + ν i∞ (p − p io ) / RT where the superscript “o” refers to the reference condition. If experimental solubility data is to be matched using regression, this method for defining the solubility parameters must be used. Correlation values can be entered in the table by selecting Aqueous Solubility| Calculate component solubility parameters from the menu. Methods 2) or 3) will be used if the solubility parameters are all set to zero. This can be done by selecting Aqueous Solubility|Reset solubility parameters to zero from the menu. If the reference solubility parameters are set to zero in the component table, Henry’s constants will be estimated internally for all components for each Oil-Gas-Water flash. Method 2) may be overridden by specifying component Henry’s constants for individual OilGas-Water flash calculations. 40 • Components
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Ideal Gas Enthalpy Coefficients: The ideal enthalpy at a given temperature T is calculated from a polynomial expression that takes the following form:
H ideal = H A + H B * T + H C * T 2 + H D * T 3 + H E * T 4 + H F * T 5 where the temperature T is in °R. The ideal enthalpy coefficients HA through HF should be specified in units to give Hideal in Btu/lb.
Component Heating Values: The heating value of a component is the heat of combustion assuming the reaction goes to completion i.e. the reaction takes place with excess oxygen and the final products are carbon dioxide and water. In SI system the units are kcal/gmol and in Field units are Btu/gmol. Approximate values have been assigned to the Library components. These values were taken from the CRC Handbook of Chemistry and Physics, 65th edition, CRC Press Inc, 1984, pages D275-D280 (see table below). WinProp will write out the HEATING_VALUES keyword and the associated values to the .gem output file. This file can then be referenced by a GEM data file using an include statement or the contents of the .gem file can be copied and pasted at the appropriate location in the GEM data file. Currently for pseudo components created by WinProp’s splitting and or lumping options, no method has been coded for estimating the heating value; accordingly for pseudo components values of zero are assigned. However heating values for pseudo components can be estimated based on the values assigned to the library components given the actual composition of the pseudo component is known. Once these values are estimated simply edit the values in the last column of WinProp’s component properties form and save the form. For example for pseudo component c2-c3 assuming a split of 50% c2 and 50% c3 and using the built in values in WinProp the heating value is calculated by mole fraction averaging as: 0.5*1478.46+0.5*2105.16 = 1791.81 Btu/gmol. Values for other pseudo components such as c4-c6 can be estimated in a similar manner. For the plus fraction such as C10+ if the breakdown of the carbon number vs. mole fraction is known then mole fraction averaging can be applied. If the distribution is not known then assign the value corresponding to the presumed largest mole fraction carbon number, for example for C10+ this might be C12. The heating value for the library component FC12 of 7722.09 Btu/gmol would then be assigned to C10+. GEM will calculate and report the heating value of all the well streams in the output file using the known composition of the stream by mole fraction averaging the entered component heating values supplied by the user. Once the HEATING_VALUES keyword appears in a GEM data file a heating value for the separator gas stream for wells and groups will be calculated and be available for plotting with RESULTS. The heating value assigned to the library components in WinProp are shown below. For the carbon fraction FC7-FC45 the heating value equals 1002.57 kcal/gmol + 157.44 kcal/gmol increment for every carbon number greater than 6. Same values are used for NC6 and FC6 and NC7 and FC7 etc. For pseudo components values of zero will be assigned, as at present there is no method implemented for estimating these values.
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Components • 41
Component Name H2S N2 CO2 CH4 (or C1) C2H6 (or C2) C3H8 (or C3) IC4 NC4 IC5 NC5 FC6 FC7 FC8 FC9 FC10 FC11 FC12 FC13 FC14 FC15 FC16 FC17 FC18 FC19 FC20 FC21 FC22 FC23 FC24 FC25 FC26 FC27 FC28 FC29 FC30 FC31 FC32 FC33
42 • Components
Heating Value (Btu/gmol) 0.0 0.0 0.0 844.29 1478.46 2105.16 2711.54 2711.54 3353.66 3353.66 3975.91 4600.28 5224.64 5849.00 6473.36 7097.73 7722.09 8346.45 8970.82 9595.18 10219.54 10843.91 11468.22 12092.63 12717.00 13341.36 13965.72 14590.08 15214.45 15838.81 16463.17 17087.54 17711.90 18336.26 18960.63 19584.99 20209.35 20833.71
User's Guide WinProp
FC34 FC35 FC36 FC37 FC38 FC39 FC40 FC41 FC42 FC43 FC44 FC45 NC6 NC7 NC8 NC9 NC10 NC16 TOLUENE BENZENE CYCLO-C6 H2O
21458.08 22082.44 22706.80 23331.17 23955.53 24579.89 25204.26 25828.62 26452.98 27077.35 27701.71 28326.07 3975.91 4600.28 5224.64 5849.00 6473.36 10219.54 3705.97 3097.15 3715.32 0.0
Example: Consider an 8-components fluid, with the last three components being pseudo components. In Field units, the heating values as written out by WinProp would result in the following lines appearing in the .gem output file: *NC 8 3 *COMPNAME 'CH4' 'C2H6' 'C3H8' 'NC4' 'NC5' 'FRAC1' 'FRAC2' 'FRAC3' *HEATING_VALUES 844.29 1478.46 2105.16 2711.54 3353.66 0.0 0.0 0.0
Interaction Coefficients Interaction coefficients (δij) are introduced to account for the molecular interaction between dissimilar molecules. Their values are generally obtained by fitting the predicted saturation pressures to experimental data. Interaction coefficients for component pairs are shown on Tab Int. Coef.. An example is shown below.
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Hydrocarbon-Hydrocarbon Interaction Coefficients The hydrocarbon (HC) components are identified by a value of 1 in the “HC” column on Tab Component. The interaction coefficients between HC components are calculated from ⎛ 2v1ci/ 6 v1cj/ 6 ⎞ δ ij = 1 −⎜ 1 / 3 1 / 3 ⎟ ⎜ v +v ⎟ ci ⎠ ⎝ ci
θ
where vci is the critical volume of component i, and θ is the hydrocarbon – hydrocarbon interaction coefficient exponent. It has been shown that a value of 1.2 provides a good match of the paraffin – paraffin interaction coefficients of Oellrich et al (1981). However, it is recommended that this value be obtained by matching experimental data (e.g. saturation pressure data). To avoid cluttering the table of interaction coefficients, the HC interaction coefficients are not shown when the form is loaded. To view them, click on Show HC Int. Coef. button. To hide them, click on Hide HC Int. Coef. button. With this version of WinProp, it is possible to define multiple HC:HC interaction coefficient groups, each with its own value of the exponent. HC:HC groups can also be selected as independent parameters in regression, please see the chapter on “Regression”. The list of groups currently defined is shown in the list box with the caption HC Int. Coef. Exp.. The entries include a name and in brackets the value of the exponent. To see the group ID for all HC-HC pairs on the interaction coefficient table, click on the Show HC-HC Group(s) on grid button.
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The value of the exponent for a given group(s) can be changed by invoking a custom form designed to handle the tasks associated with managing these groups. This form is invoked by clicking the button on the Int. Coef. tab with the caption HC:HC Groups / Apply value to multiple non HC-HC pairs…. This form is shown below.
The currently selected group is shown under the Name label. The list of pairs that belong to this group is shown in the list box labeled Selected pairs. The user can scroll through all defined groups in the drop down list box under the Name label. The full list of pairs that do not currently belong to any group can be seen on the list box under the Select pairs frame. These pairs can be assigned to any defined group(s). If any “orphans” remain when this form is saved then these are assigned to the default group, i.e. group # 1. Initially only a single group is created with the exponent value of 1.2. The value of the exponent can be changed via the text box with the label Exponent value. All HC:HC pairs initially belong to this group. To create a new group first select the HC:HC option button under Type and then click on the Create New button. This new group will be assigned the name HcIntCoefExp-2 with a value of 1.2 for the exponent. For pairs to be assigned to this new group # 2, group #1 must first relinquish these. This is done by first selecting group # 1 from the group list, identifying the pairs that will be removed (by pressing the left mouse button while holding the CTRL key down) from the Selected pairs list box and then clicking on the Delete selection(s) button. These pairs will be removed from group # 1 as reflected in the revised list in the Selected pairs box. To pick these pairs up for group # 2, change the name to group # 2, select pairs by highlighting and then pressing the Apply selection(s) button. At least one pair must be assigned to each group and a given pair can be assigned to a single group only. To delete a group click on the Delete Group button. User's Guide WinProp
Components • 45
Other Interaction Coefficients Interaction coefficients between nonhydrocarbons, and between hydrocarbons and nonhydrocarbons from the WinProp library are displayed in the table. They may be edited in one of two ways, either directly on the grid, or if a common value is to be assigned to multiple pairs, say CO2 and all pseudo-components then a faster way is through a special form invoked by the clicking the button on the Int. Coef. tab with the caption HC-HC Groups / Apply value to multiple non HC-HC pairs…. Select pairs through the 1st index (single) and 2nd index [multiple] lists and then click on the Apply selection(s) button. The list of pairs chosen is shown in the Selected pairs box. Specify the value to be applied in the text box labeled Value and finally click on the Apply value button. On exiting the form, the interaction coefficient table should now show the revised value for the pairs selected. Note that as δij ≈ δji, changing one also changes the other.
Viscosity Parameters There are two types of viscosity correlation available in WinProp: the Jossi, Stiel and Thodos (JST) correlation as described in Reid et al. (1977), and the Pedersen corresponding states correlation as presented in Pedersen et al. (1984) and Pedersen and Fredenslund (1987). The viscosities of liquid and vapor phases are calculated with the same correlation. The choice of correlation is made on the Viscosity tab of the Component Selection/Properties form by selecting one of the option buttons under Viscosity Model Type.
Jossi-Stiel-Thodos Correlation An example of the data entry form for the JST correlation is shown below.
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The JST correlation determines the mixture viscosity from the low-pressure mixture viscosity according to the following function:
[ ( μ − μ )ξ + 10 ]
− 4 0.25
*
Where μ μ∗ ξ M ρr
= = = =
= a 0 + a 1ρ r + a 2 ρ 2r + a 3 ρ 3r + a 4 ρ 4r
Oil or gas viscosity in cP or MPa⋅s Low-pressure viscosity in cP or MPa⋅s Group Tc1/6 M-1/2 Pc-2/3 where Tc is in K and Pc is in atm molecular weight Reduced molar density, ρ/ρc = vc/v
Two options are available for calculating the low-pressure mixture viscosity. The YoonThodos + Herning-Zipperer method computes low pressure component viscosities according to a formula developed by Yoon and Thodos and then computes the mixture viscosity according to the mixing rule of Herning and Zipperer. Both of these formulas are reported in Reid et al. (1977). The Lee-Eakin method calculates the low-pressure mixture viscosity directly using a correlation based on the molecular weight of the mixture presented by Lee and Eakin (1964). The value of ξ is calculated by first obtaining mole – fraction weighted average values for the mixture critical temperature, pressure and molecular weight. The mixture critical volume vc is calculated from: 1/ α
⎛ nc ⎞ α⎟ v c = ⎜ x i v ci ⎜ ⎟ ⎠ ⎝ i =1
∑
Where α is the mixing exponent parameter, xi is the composition and vci is the critical volume for viscosity calculation (vc(viscosity) on Tab Component). α, a0, a1, a2, a3, and a4 are entered on Tab Viscosity. Default values are shown when the form is first activated. As well as the correlation coefficients (α, ai) and critical volumes for viscosity (and to a lesser extent, the critical temperatures and pressures), the JST method depends very strongly on the density of the mixture predicted by the equation of state. Thus, use of the JST correlation may result in large errors if the phase densities are incorrect. It is recommended that the EOS be tuned to match volumetric data before attempting to predict or match viscosities with the JST correlation.
Pedersen Correlation The Pedersen viscosity correlation uses the principle of corresponding states to calculate the viscosity of a component or mixture, knowing the viscosity of a reference substance at the same conditions of reduced pressure and temperature. The deviation from simple corresponding states is accounted for by a “rotational coupling coefficient,” α. The viscosity of the mixture is calculated according to the following formula: μ mix ( P, T ) ⎛ Tc,mix =⎜ μ o (Po , To ) ⎜⎝ Tc,o User's Guide WinProp
⎞ ⎟ ⎟ ⎠
−1 / 6
⎛ Pc,mix ⎜ ⎜ P ⎝ c ,o
⎞ ⎟ ⎟ ⎠
2/3
⎛ MWmix ⎜⎜ ⎝ MWo
⎞ ⎟⎟ ⎠
1/ 2
⎛ α mix ⎜⎜ ⎝ αo
⎞ ⎟⎟ ⎠ Components • 47
Where μ Tc Pc MW α
= = = = =
Viscosity Critical temperature Critical pressure Molecular weight Rotational coupling coefficient
The subscript “mix” refers to the mixture property, and the subscript “o” refers to the reference substance property. The reference substance for the Pedersen model is methane. The mixture critical temperature and pressure are calculated using mixing rules that are a function of the component critical temperatures and pressures and mole fractions. The molecular weight of the mixture is determined from:
(
)
MWmix = b1 MWwb 2 − MWnb 2 + MWn where MWw is the weight fraction averaged molecular weight, and MWn is the mole fraction averaged molecular weight. The rotational coupling coefficient is calculated as follows: α = 1 + b 3 ρ br 4 MW b5 where ρr is the reduced density of the reference substance. The viscosity of a mixture calculated using the Pedersen model depends strongly on the critical pressures, critical temperatures and molecular weights of the components, and the coefficients bi shown in the above two equations. Two different versions of the Pedersen correlation may be chosen. The one labeled Modified Pedersen (1987) uses a modification to the methane viscosity equation as described in Pedersen and Fredenslund (1987). This modification showed improved results for mixture viscosities up to approximately 10 cP. Each modification has a set of default coefficients. These coefficients may be modified during regression to match experimental viscosity data.
Aqueous Phase The Aqueous phase tab is used for setting properties of the water phase for use in multiphase Oil-Gas-Water calculations. The form is shown below.
Aqueous Phase Salinity The salinity of the aqueous phase is expressed as NaCl concentration. The units available for specifying the brine salinity are weight fraction, molarity, grams of NaCl per litre of water, molarity, and mole fraction. All other water properties are determined from correlations. The brine salinity is used to adjust the internally estimated Henry’s constants for the library components N2, CO2, H2S, C1, C2, C3, iC4, nC4, iC5, nC5, nC6, nC7 and nC8 to account for the salting-out effect. Note that this adjustment is not performed when solubility parameters are specified in the component table, or when Henry’s constants are entered for individual flash calculations.
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Henry’s Law Constant Correlation There are two correlations available in WinProp to calculate Henry’s law constant: the Harvey’s method (1996), and the Li-Nghiem’s method (1986). The effect of salt on the gas solubility in the aqueous phase is modelling either by salting-out coefficient or the scaledparticle theory, depending on the component. The choice of Henry’s constant correlation is made by selecting one of the option buttons in the Henry’s law constant correlation frame in the Aqueous phase tab. The correlation is set to Harvey’s method (1996) by default.
Activation of Second Set of Component Properties WinProp supports the specification of a second set of EOS component properties. It is often difficult for a single EOS description to perform adequately over a wide range of conditions encountered in reservoir phase behavior modelling. This can be alleviated by the introduction of a second EOS model that is applied to calculations performed at surface (separator) conditions, while the first EOS set is used for calculations at reservoir conditions. Therefore separator data can then be matched separately from other PVT data gathered at reservoir temperature, for example by CVD and differential liberation experiments. To activate the second set select Options|Enable Second Set. This should be done after the component selection is completed. WinProp will duplicate the first set properties for the second set. The user can toggle between the first and second set using the Set Selection menu. Certain operations, for example addition or removal of components on the component form, can be performed only if the first set is active. Currently critical pressure, critical temperature, volume shift, omega-A, omega-B, interaction coefficient exponent and interaction coefficients for pairs with a nonhydrocarbon component are User's Guide WinProp
Components • 49
supported for the second set. The user can edit the values of these properties from the default assignments. The user can also reset back to the original values by selecting Set Selection|Reset 2nd to 1st. The second set parameters can also be used in regression. To use a second set parameter in regression the user does not have to enable the second set component properties first. The second set parameters can be selected directly on the Regression Parameters form in a manner similar to first set properties. The initial value of the property will be set equal to the corresponding first set parameter. The second EOS parameter set, when enabled, is used in performing the following calculations: separator, separator calculation associated with the constant volume depletion experiment (to determine yields at surface) and in differential liberation experiment when flashing the residual oil (at atmospheric pressure and reservoir temperature) to standard conditions (atmospheric pressure and temperature).
GEM Fluid Model Generation and Component Properties Printing The EOS model description in WinProp can be written to a file in a format suitable for CMG's compositional simulator GEM. This file can be imported into a GEM data set using Builder. The model information includes EOS type, component critical properties, volume shifts, EOS omega parameters, parachors, aqueous solubility parameters and viscosity model coefficients. The component properties can also be echoed to the output file. The option to write out the EOS model may be included in the data set by selecting Simulator PVT|CMG GEM EOS Model from the menu. A form entitled CMG GEM EOS Model will be included in the data set. In the File Selection frame on this form there are two check boxes for printing the component properties. Select the upper check box to print detailed component properties to the output file, and select the lower check box to write out the EOS model for GEM. This file will have the same root name as the data file and the extension (.gem). To complete the model description for GEM, a reservoir temperature must be specified. If the data set includes a laboratory experiment simulation such as a CCE, CVD or Differential Liberation calculation, the temperature from the first calculation of this type in the data set will be taken as the default reservoir temperature, otherwise this field must be filled in by the user. There are also options to Write solid model parameters for GEM, and to Write component heating values for GEM. To use the solid model in GEM, the number of solidforming components must be set to one on the “Asphaltene/Wax Modelling” dialog. GEM’s solid model is used for asphaltene precipitation, not for waxes. To have accurate parameters for GEM, the reference fugacity for the model should be determined from experimental data as described in the “Asphaltene/Wax Modelling” section of the User’s Guide. Parameters for the isothermal precipitation model will always be written for GEM. Temperature-dependent parameters will only be written if additional onset pressures have been specified with the reference fugacity calculation.
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In the Interaction Coefficient Table frame, the format of the table can be selected as either upper or lower triangular form. By default, the aqueous phase solubility parameters are not printed with the other component properties. To turn on this option, select the check box in the Solubility Parameters frame. If an Oil-Gas-Water flash is included in the data set before the print options form, the Henry’s constants and molar volumes at infinite dilution used in the flash will be available for printing. Optionally, the parameters may be recalculated at a specified pressure and temperature before printing.
Importing Components with the Table Import Wizard The Table Import Wizard is a tool designed to assist the user in importing Excel™ or ASCII format data into WinProp. General instructions regarding use of the Wizard are given in the “Tutorial” section of this manual. Specific information relating to the import of component properties is given here. The Table Import Wizard can be used to append or insert components at the currently selected row in the component table. The wizard is launched by clicking on the Table Import Wizard button located on the Component tab. Components can only be imported when the first set of EOS properties is active. Data for any of the component properties appearing on the component table may be imported. When importing component properties, the only specifically required information is a component name. A further requirement, however, is that a minimum set of data sufficient to estimate any component properties not imported must be provided. This minimum set of data may be either (a) two of the following properties: specific gravity, molecular weight or normal boiling point, or (b) both of critical temperature and critical pressure. Depending on which component properties have been imported, a form for the selection of physical and critical property correlations required to complete the component specification may appear when the table import wizard exits. The use of these correlations is discussed earlier in this chapter under “Component properties”, in the section on “User components with known SG, Tb and MW.” Once these correlations have been selected, the process is completed by inserting all imported properties into the table and calculating the values of all properties that were not imported. Note that the Table Import Wizard cannot be used to import columns of data for existing components. The standard Windows cut, copy and paste functions can be used for this purpose.
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Components • 51
Common Data Required for All Options
Overview This chapter describes the common data required for most calculations. These include Composition specification, Initial K-values, Output level, and Stability test level. Generally, the built in default values are used in the calculations. The saturation pressure calculation, which is common to most laboratory experiment simulation options, is discussed in the next chapter.
Composition Specification Compositions are entered in moles or in weight units, specified as fraction or percent. Values are normalized internally. If weight fractions or percents are entered, they are converted internally to mole fractions. To use weight units, select the appropriate option on form Titles/EOS/Units. The table on form Composition contains two columns for composition input. The primary composition corresponds generally to the composition of the oil or gas in place. Values must be entered for the primary composition. The secondary composition corresponds normally to the injected fluid. The secondary composition need not be entered and will default to zero. An example of form Composition is shown below.
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Common Data Required for All Options • 53
Several composition sections can be defined in a data set. All calculations following a composition section will use the composition of that section until the end of the run or another composition section is encountered. In the following example, the fluid composition from Well 16 is used for a series of calculations. Similar calculations are then performed with the fluid composition of Well 20.
Composition Used in Calculations
The feed composition used for all calculation options can be •
a mixture of the primary composition and the secondary composition
•
the feed from the previous calculation option
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•
the vapor composition from the previous calculation option
•
the liquid composition from the previous calculation option
•
the composition from Phase n from the previous calculation option
The feed composition is specified from the Combo Box Feed, located on the last tab of most calculation options. The selection of the feed composition for a two-phase saturation pressure calculation is shown above. In this example, the composition that enters into the two-phase calculations is a mixture containing 80 mole % of the primary composition and 20 mole % of the secondary composition. When Phase is selected, you enter the Phase Number in the adjacent text box. Some calculations accept only the Mixed and Previous option. The Combo Box Feed displays only these items in this case.
Initial K-Values Initial K-values are required to start most calculations. These can be •
estimated internally from Wilson’s equation (Internal), i.e. ln K i =5.37 (1 + ωi ) (1 − Tci / T )+ln ( p ci / p)
•
from a previous two-phase calculation (Previous)
•
from Phase n of a previous multiphase calculation (Phase)
When Phase is selected, the Phase Number is entered in the adjacent text box.
Output Level The Output level for a normal run is 1. If more information is required, for example the results of each iteration of a flash calculation, select an Output level value of 2.
Stability Test Level In phase behavior calculations, the number of phases is generally unknown a priori. WinProp assumes that the system is initially single-phase and performs a stability test on that system. The stability test is a calculation that determines whether a system needs to split into additional phases to achieve stability. The stability test searches the multidimensional Gibbs free energy surface for stationary points. For a phase to be stable, the Gibbs free energy must be lower than the value at all stationary points. The Stability test level determines the thoroughness of the search for the stationary points. Values are from 0 to 4. For most two-phase oil/gas systems, Level 1 is normally sufficient. For systems with more than two phases, a value of 4 may be required. The Stability test level is set to its default value when the form for a particular calculation is first activated. If you suspect that your system may have more phases than those predicted, increase the level value and rerun the data set. See Nghiem and Li (1984) for a detailed discussion of stability test calculations.
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Common Data Required for All Options • 55
Two-Phase Saturation and Phase Boundary Calculations
Overview This chapter describes calculations for mixtures on the phase boundaries: •
Bubble point and dew point calculations
•
Phase boundary diagram construction (pressure-temperature, pressure-composition, temperature-composition and pseudo-ternary)
•
Critical-point calculation
•
Multiple-contact calculation
The phase boundary calculations can also generate lines of constant phase mole fraction or lines of constant volume fraction (quality lines).
Saturation Pressure This option is invoked by selecting Calculations|Saturation Pressure. An example data set for this option is sat-pressure.dat. For data entry corresponding to items on tab 2, that is Feed, K-values, Output level and Stability test level specifications, see the Chapter “Common Data Required for all Options”. A value of the temperature at which the saturation pressure is to be calculated is required. Enter a value in the text box labelled Temperature. An estimate of the saturation pressure is also required; enter a value in the text box labelled Saturation Pressure Estimate. If this is a poor estimate, ask WinProp to generate internally a better initial guess for saturation pressure calculation by checking the box Improve saturation pressure estimate. Details of the calculation techniques can be found in Nghiem et al. (1985). Finally at a given temperature there are two saturation pressures, the upper and lower values respectively. The upper value can be a dew point or bubble point fluid, the lower is a dew point fluid. By default the upper value is calculated as this corresponds to the reservoir saturation pressure at the given temperature. The lower value can be chosen instead by selecting the button Lower dew point in the frame labelled Calculation option. Experimental data related to a saturation pressure calculation that can be matched via regression are shown on the table on the first tab, Calculations. These include saturation pressure, liquid and vapor mass densities, compressibilities and viscosities. The weight assigned to each experimental data value can also be specified. User's Guide WinProp
Two-Phase Saturation and Phase Boundary Calculations • 57
Saturation Temperature This option is invoked by selecting Calculations Saturation Temperature. An example data set for this option is sat-temperature.dat. For items on tab 2, Feed, K-values, Output level and Stability test level specifications, see the Chapter “Common Data Required for Options”. A value for the pressure at which the saturation temperature is to be calculated is required. Enter a value in the text box labelled Pressure. An estimate of the saturation temperature is also required; enter a value in the text box labelled Saturation Temperature Estimate. If this is a poor estimate, ask WinProp to generate internally a better initial guess for saturation temperature calculation by checking the box Improve saturation temperature estimate. Generally there are two possible values for the saturation temperature at a given pressure. The larger value corresponds to a dew point fluid whereas the lower value corresponds to a bubble point fluid. By default the larger value is calculated. The lower value is chosen by clicking on the button Lower sat. temperature in the frame labelled Common options. Details of the calculation techniques can be found in Nghiem et al. (1985). Experimental data related to a temperature pressure calculation that can be matched via regression are shown on the table provided on tab Calculations. These include saturation temperature, liquid and vapor mass densities, compressibilities and viscosities. The weight assigned to each experimental data value can also be specified.
Phase Boundary and Quality Line Calculations This option is invoked by selecting Calculations|Two-phase Envelope. Example data sets for this option are envel_2ph-pt.dat (PT diagram), envel_2ph-px.dat (PX diagram) and envel_2ph-tern.dat (ternary diagram). The two-phase envelope calculation generates the boundaries between the single-phase and two-phase regions. The bubble point envelope corresponds to the boundary between a singlephase liquid region and a two-phase vapor-liquid region; the dew point envelope corresponds to the boundary between the single-phase vapor region and the two-phase region. There are two main classes of diagrams that can be generated: X-Y phase diagrams and pseudo-ternary phase diagrams. Pseudo-ternary phase diagrams depict the boundaries between single-phase and two-phase regions in composition space at a fixed temperature and pressure. The results are displayed on a triangular diagram, where each apex of the triangle corresponds to 100% of one pseudocomponent. Each component in the system is assigned to one of the three pseudo-components. X-Y phase diagrams are displayed on regular Cartesian coordinates. The types of envelopes or diagrams that can be generated are: •
Pressure-Temperature (PT) diagram
•
Pressure-Composition (PX) diagram
•
Temperature-Composition (TX) diagram
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In the process of constructing the envelope, WinProp also calculates the location of critical points through interpolation. This is a very efficient method for estimating critical points if they exist on the portion of the phase envelope being constructed. A direct method of calculating critical points is also available (see the section on “Critical point calculation”). A typical PT diagram is shown below: Gas condensate Phase Envelope Pressure-Temperature Diagram 14,000
2-Phase boundary 99.000 volume % 90.000 volume % 75.000 volume % 60.000 volume % 55.000 volume % 50.000 volume % 45.000 volume % 40.000 volume %
12,000
Pressure (psia)
10,000
8,000
Critical 95.000 volume % 80.000 volume % 70.000 volume % Critical 55.000 volume % 50.000 volume % 45.000 volume % 35.000 volume %
6,000
4,000
2,000
0 -200
0
200
400
600
800
Tem perature (deg F)
Envelope Specification The type of envelope to be calculated is specified on tab Envelope Specification. First, select either X-Y Phase Envelope or Pseudo-Ternary Phase Envelope at the top of the tab. This selection will activate the corresponding data entry area. X-Y Phase Envelope For X-Y phase envelopes, you must select which variable to use on the X-axis (independent variable) and the Y-axis (dependent variable). The choices are Temperature and Composition for the X-axis and Pressure or Temperature for the Y-axis. For a Pressure-Temperature (P-T) diagram select Temperature as the independent variable and Pressure as the dependent variable. For a Pressure-Composition (P-x) or swelling curve select Composition as the independent variable and Pressure as the dependent variable. Finally for a Temperature-Composition (T-x) diagram select Composition as the independent variable and Temperature as the dependent variable. The envelope is generated by taking steps in terms of the independent variable, and determining the corresponding value of the dependent variable on the phase boundary. Minimum and maximum values for the X- and Y- variables are specified along with the axis definitions. The calculation stops when any of these limiting values are exceeded. When composition is selected as the independent variable, minimum and maximum independent variable step sizes are also specified, as well as the upper and lower limits for the axis. P-x and T-x diagrams are generated by adding a fluid defined by the secondary composition on the last Composition form to the fluid defined as the feed for the envelope calculation.
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Two-Phase Saturation and Phase Boundary Calculations • 59
For P-T diagram the value entered in the Temperature combo box is taken as the initial starting point for the calculation on the upper saturation pressure curve. Two types of curve(s) can be generated, line(s) of constant mole fraction of the vapor phase or line(s) of constant volume fraction vapor phase. The latter are also known as quality lines. These are specified on Tab 2, “Envelope Construction Controls” on the table in the frame labelled “Quality/Mole Fraction Lines Specification”. If a value of (x) is chosen for a line, then a value of (1-x) is automatically selected as well. This ensures that a starting point on the upper saturation pressure curve at the initial temperature is always selected whether there is a dew point or a bubble point. This also means that for example if x = 0.0 is selected and the upper saturation pressure is a bubble point then the program will attempt to trace from the bubble point line (x=0.0) as well as the lower dew point (for 1-x=1.0). However the chances are that the attempt to trace from the lower dew point will fail as the algorithm has difficulties starting off from very small pressures. To select only the starting point corresponding to value (x) check off the box labelled “Select value from the above table as well as one minus the value in the table”. This implies the user knows the type of upper saturation pressure, dew point or bubble point. The algorithm will attempt to generate both the part corresponding to the value (x) as well as (1-x) for all starting points. For example if x = 0, is chosen then both the bubble and dew point curves will be generated. All values should be between 0 and 1. A maximum of 25 such lines can appear on a single plot. By default a single value corresponding to vapor phase mole fraction equal to 0.0 is pre-selected. If x = 1.0 is selected and both an upper and lower dew point exists, the starting point on the upper dew point will be selected. If starting points on both upper and lower dew point curves is desired then check on the box labelled “Trace from all potential starting points” on Tab 2. The value entered in the Pressure combo box, either a number or the selection Unknown may be used as the initial guess for saturation pressure at T = Ts if a 2 phase region cannot be found at T= Ts by scanning the interval from Pmax to Pmin. For the majority of cases a value is not required for the Pressure. When composition is selected as the independent variable, both pressure and temperature must be entered, although the value corresponding to the dependent variable will be determined internally. In the unlikely scenario that this cannot be done the value entered for the dependent variable will be used as an initial guess in the saturation calculation. The initial composition is taken as that defined by the Feed specification for the envelope calculation. The values entered for Mole fraction vapor (Fv) or Volume fraction vapor (Vv) are used to define which lines on the phase envelope are generated. If a critical point is encountered, the line corresponding to (1- Fv) will also be calculated. For example, with Fv=1, the entire phase boundary (starting on the dew point side) will be calculated. If a value is specified for volume fraction vapor, the quality line corresponding to Vv will be calculated. Again, if a critical point is encountered, the line corresponding to (1-Vv) will also be calculated. To calculate phase boundaries, select Fv = 0.0 and/or 1.0 or Vv = 0.0 or 1.0. When tracing lines of constant volume fraction, an additional stopping constraint can be placed on the calculation by specifying minimum and maximum allowed values of vapor mole fraction. By default these values are set to –10 and +10 respectively, thus the calculation will not halt unless large nonphysical values of the vapor mole fraction are calculated.
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Pseudo-Ternary Phase Envelope The first step in generating the pseudo-ternary phase envelope is specification of the pseudocomponents. When the Pseudo-Ternary option is selected, a grid is displayed listing all of the components. The primary and secondary compositions are shown to assist the user in defining the pseudo-components. Components are assigned to pseudo-components by entering the number 1, 2 or 3 in the column of the table labeled “Pseudo.” Pseudo-component 1 is at the lower left corner of the triangle, 2 is at the lower right, and 3 is at the top. The diagram is generated by locating the point on the diagram corresponding to the specified mole or volume fraction vapor for the feed composition. The composition of the phase in equilibrium with this phase is obtained from the K-values. A step in the construction is taken by adding fluid with the secondary composition, and the next point is calculated with this new composition. Note that different pseudoization schemes will result in different envelopes being generated. As for the X-Y diagram, minimum and maximum values for the mole fraction of secondary fluid can be specified, as well as minimum and maximum secondary fluid step sizes. Pressure and temperature must be specified, as they are fixed for the ternary diagram. Mole fraction vapor, volume fraction vapor, minimum mole fraction vapor and maximum mole fraction vapor may be specified as discussed under X-Y Phase Envelopes.
Envelope Construction Controls Maximum Number of Points This value corresponds to the maximum number of points calculated on the phase diagram. Initial Step Size The Initial step size controls the spacing between the calculated points on the envelope. Both positive and negative values may be used. For positive values, the diagram is traced initially in the direction of increasing x-values. For negative values, the diagram is initially traced in the direction of decreasing x-values. WinProp internally estimates the step size for subsequent points on the envelope. Independent Variable Interpolation Points These correspond to x-values for which you want calculated y-values. Because the step size in the envelope calculation is automatic, these interpolation values must be entered to force calculations at desired x-axis values. Stability Test WinProp checks the stability of each phase for every calculated point on a phase envelope. The envelope generation routine can be set to terminate when an instability is detected, or to continue calculations. Letting the calculation continue along unstable lines is sometimes useful, as it allows determination of two stable portions of a phase envelope that are connected by an unstable line.
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Cricondenbar/Cricondentherm Calculation The cricondenbar corresponds to maximum pressure on the PT phase envelope whereas the cricondentherm corresponds to the maximum temperature. These are estimated in a twophase PT envelope construction (see “Phase boundary and quality line calculations”) or can be calculated directly by selecting Calculations|Cricondenbar/-therm. An example data set for this option is cricon.dat. For Feed, K-values, Output level and Stability test level specifications, see the Chapter “Common Data Required for all Options”. As initial guesses for pressure and temperature, you can specify Unknown or Previous (value from the previous calculation option), or type in the value of the initial guess.
Critical Point Calculation The phase-boundary and quality-line calculations estimate the critical point through interpolation. This method is efficient and yields both the phase boundary and critical points. However, if you want a direct calculation or want to match a critical point in a regression calculation, you should use the Critical Points Calculation option. The critical points calculation is invoked by selecting Calculations|Critical Points. An example data set for this option is critical.dat. This option uses the calculation method of Heidemann and Khalil (1980). The required numerical data are the Lower dimensionless volume limit and the Upper dimensionless volume limit. These dimensionless volumes are equal to the ratios of molar volume v over the parameter b of the EOS. All critical points between these two volume limits are calculated. Default values for these limits are 1.0 and 5.0 respectively. You can enter the experimental critical pressure and temperature for regression purposes.
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Flash Calculations
Overview Flash calculations determine the split of a system at a given pressure, temperature and feed composition. The number of phases and the properties for each phase are calculated. WinProp can perform many types of flash calculations: 1. Two-phase vapor-liquid 2. Three-phase vapor-liquid_1-liquid_2 3. Three-phase vapor-liquid-aqueous 4. Four phase flash calculation (fluid phases only) 5. Multiphase flash calculations with a solid phase 6. Isenthalpic flash calculation In the above calculations, the fluid phases are modeled with an EOS, except for Calculation No. 3 where the component solubility in the aqueous phase is modeled by Henry's law. Calculation No. 5 can be used for modelling asphaltene and wax precipitation. Flash calculations performed in the single-phase region will yield a single-phase system. An option for singlephase calculation is also available in WinProp and is described in this chapter. Common input for two-phase flash, multiphase flash and asphaltene/wax modelling calculations is described below, followed by descriptions of each of the flash types.
Common Input for Two-Phase Flash, Multiphase Flash and Asphaltene/Wax Modelling Calculations For Feed, K-values, Output level and Stability test level specifications, see the Chapter “Common data required for all options”. Flash calculations are performed at the pressure and temperature specified in the Text Boxes labeled Pressure and Temperature. You can perform a series of calculations by specifying the Pressure Steps, Temperature Steps, or Mole Fraction Steps with the associated number of steps. The steps can be positive or negative. Step No. 1 corresponds to a calculation at the specified pressure and temperature or mole fraction. Specifying steps for the primary mole fraction allows calculations for a number of mixtures of the primary and secondary fluids.
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When a series of flash calculations have been specified by setting temperature, pressure or mole fraction steps, plots of the phase properties can be generated. Specification of the phase properties (maximum of three) to plot is done on tab Plot Control. When plotting is activated, steps can be specified in one or two of the variables: pressure, temperature and mole fraction. If steps are specified for only one variable, the plots are generated with that variable as the independent variable, and the phase property as the dependent variable. Up to 100 steps in the independent variable are allowed. When steps are specified for two variables, one variable is treated as a parameter variable, and curves of the phase property are displayed for each value of the parameter variable. Up to 8 steps in the parameter variable are allowed. If mole fraction steps are specified, mole fraction is always used as the independent variable. If pressure and temperature steps are both specified, pressure is used as the independent variable.
Two-Phase Flash Calculations This option is invoked by selecting Calculations|Two-Phase Flash from the menu. An example data set is flash-2ph.dat. For specification of data on the Calculations tab and the Plot Control tab, please see the section “Common input for two-phase flash, multiphase flash and asphaltene/wax modelling calculations” at the beginning of this chapter. The Flash type may be set to either QNSS/Newton or Negative. Selecting QNSS/Newton specifies that the two-phase flash equations will be converged initially using a Quasi-Newton successive substitution algorithm, followed by Newton’s method to refine the roots. If the system is in the single-phase region, properties for that phase will be reported, and k-values will not be calculated. When the Negative flash is selected, the QNSS algorithm is used without further refinement of the roots. If the system is in the single-phase region, properties for two phases will be reported, with one phase being present in a negative (non-physical) amount. This option allows generation of k-value estimates outside of the two-phase region. Experimental data to be included in a regression calculation are entered on tab Experimental and Experimental K-values. Data on tab Experimental include mass densities, mole fractions, volume fractions, compressibility factors, and viscosity of both the vapor and liquid phases. Experimental K-values are entered on tab Experimental K-values.
Multiphase Flash Calculations This option is invoked by selecting Calculations|OGW/EOS Multiphase Flash. An example data set is flash-3ph.dat. For specification of data on the Calculations tab and the Plot Control tab, please see the section “Common input for two-phase flash, multiphase flash and asphaltene/wax modelling calculations” at the beginning of this chapter. The type of multiphase calculation to be performed is selected with the Combo Box Flash type. The 3-phase and 4-phase calculations use the techniques described in Nghiem and Li (1984). This is a stage wise procedure where the number of phases is gradually increased. All phases are modeled with an EOS. The number of phases selected from the Combo Box corresponds to the maximum number of phases. Thus, selection of a 4-phase calculation for a two-phase system will yield the same results as a two-phase flash calculation. 64 • Flash Calculations
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The Oil-Gas-Water (OGW) calculation involve a three-phase calculation where the vapor and liquid phases are modeled with an EOS while the aqueous phase is modeled with Henry' law. An example data set is flash-ogw.dat. As the EOS was developed for gas-like hydrocarbon systems, it may not model accurately the aqueous phase. Li and Nghiem (1986) recommended the use of Henry's law constants for component solubility in the aqueous phase. The fugacity coefficient of Component i in the aqueous phase φiw is given by lnφiw = ln( H i / p)
where Hi is Henry's law constant of Component i. Hi for each component may be entered on tab Henry's Law. If Hi is not specified, WinProp will estimate it internally. See the “Components” chapter for more information on Henry’s constants. Experimental data for 3-phase and OGW calculations may be entered on tab Experimental. These include mass densities, mole fractions, volume fractions, and viscosities of the different phases. When the flash type is set to OGW, experimental data for the solubility of components in the aqueous phase may be entered on the tab labeled Exp. Solubility. The units available for specifying the component solubilities are mole fraction, weight fraction, moles per mole of water, weight per weight of water, SCF per Std. bbl of water and std m3 per std m3 of water. Values must be entered in all cells in the solubility table. Enter a value of “-1” in the table to exclude that data point from the regression. Please note that when regression is being performed on aqueous phase solubility parameters, all OGW flashes specified within the regression block must be at the same temperature. WinProp does not accept experimental data for 4-phase calculations.
Asphaltene/Wax Modelling Theoretical Background Thermodynamic Model The precipitation of asphaltene and wax phases is modelled using a multiphase flash calculation in which the fluid phases are described with an equation of state and the fugacities of components in the solid phase are predicted using the solid model described below. The solid phase can consist of one or more components. The approach for modeling asphaltene and wax precipitation is described in detail in Nghiem et al. (1993, 1996) and Kohse et al. (2000). The precipitated phase is represented as an ideal mixture of solid components. The fugacity of a precipitating component in the solid phase is: ln f s = ln f s* −
v + s R
⎡ p − p tp p * − p tp ⎤ ⎢ ⎥ − * ⎢ T ⎥ T ⎣ ⎦
ΔH tp ⎡ 1 1 ⎤ ΔC p ⎢ − ⎥− R ⎣ T T* ⎦ R
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⎡ ⎛ T* ⎞ ⎤ ⎟ − Ttp ⎛⎜ 1 − 1 ⎞⎟⎥ ⎢ln⎜ ⎜ ⎟ ⎢⎣ ⎜⎝ T ⎟⎠ ⎝ T T * ⎠⎥⎦
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where fs is the fugacity at pressure p and temperature T, fs* is the fugacity at pressure p* and temperature T*, vs is the solid phase molar volume of the component, ΔCp is the solid-liquid heat capacity difference, ΔHtp is the heat of fusion at the triple point, ptp and Ttp are the triple point pressure and temperature, and R is the universal gas constant. For isothermal predictions, this equation can be simplified to give: ln f s = ln f s* + v s (p − p * ) / RT
Characterization of the Solid Forming Components The crucial step in modeling wax and asphaltene precipitation is the characterization of the solid forming components, both in solution and in the solid phase. It was found that by splitting the heaviest components into two components, a non-precipitating and a precipitating fraction, good quantitative match with experimental data was obtained. This has been independently verified for both wax and asphaltene precipitation problems. Irreversible Asphaltene Calculations WinProp has the capability to separate asphaltene precipitate into reversible and irreversible parts. This can be useful for simulating laboratory forward or reverse contact experiments with a series of asphaltene flash calculations. Asphaltene is described as a reversible solid (S1) and an irreversible solid (S2). The conversion of S1 to S2 is described by a simple chemical reaction: S1 ←⎯→ S2 K
The rate of formation of S2 is given by: r = k 12 C1 − k 21 C 2
where C1and C2 are the molar concentrations of S1 and S2 respectively. At equilibrium, the rate is zero and the following equilibrium constant can be derived: K=
k 21 C1 = k 12 C 2
The mole fraction of reversible solid relative to the total amount of solid is: x1 =
C1 K = C1 + C 2 K + 1
and the mole fraction of irreversible solid is x2 =
C2 1 = C1 + C 2 K + 1
The procedure for simulating forward and reverse contact experiments is as follows: The first stage of the experiment can be modeled using the solid flash with the first stage oil and gas mixture. The total amount of solid precipitate will be determined from the thermodynamic model. At the completion of this calculation, the amounts of reversible and irreversible solid (x1 and x2) can be calculated from the above equations with a user-specified value of K. K = 0 indicates that all of the solid is irreversible, K = 1 gives equal amounts of reversible and irreversible solid, and K >> 1 implies that the solid is essentially all reversible. 66 • Flash Calculations
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For backward contacts, the feed to the next flash calculation is defined by taking the liquid plus the reversible solid, and combining it with injection gas. The irreversible solid is removed from the system for this flash. For forward contacts, the equilibrium vapor phase with no asphaltene is combined with fresh oil. Therefore, for forward contacts, the degree of irreversibility will not affect the calculations.
Input Data - Asphaltene/Wax Modelling You can model asphaltene or wax precipitation by selecting Calculations|Asphaltene/Wax Modelling. The approach is described in detail in references cited above. It is recommended that you go through the example data sets solid-asph1.dat, solid-phenanthrene.dat, solidwax.dat and solid-asph2.dat to get familiar with the approach. For specification of data on the Calculations tab and the Plot Control tab, please see the section “Common input for two-phase flash, multiphase flash and asphaltene/wax modelling calculations” at the beginning of this chapter. Additional plotting options are available on the tab Plot Control for Asphaltene/Wax modelling. If X-Y Plots is selected, the amount of solid in terms of weight percent precipitated can be plotted in addition to three other phase properties. Selecting Pseudo-Ternary Phase Diagram allows creation of a triangular diagram, displaying the results of flash calculations in terms of phase split (e.g. liquid-vapor, solid-liquid-vapor, solidliquid, etc.) along dilution lines. The first step is to assign each component to one of three pseudo-components by entering the number 1, 2 or 3 in the column labeled “Pseudo” in the table. Pseudo-component 1 is at the lower left apex of the triangle, 2 is at the lower right and 3 is at the top. Definition of the dilution lines is done by first selecting which two pseudo-components will be held at a fixed ratio along each dilution line. For example, setting pseudo-components A to 1 and B to 2 indicates that the base of the dilution lines will be along the bottom of the diagram, between apexes 1 and 2, and the lines will terminate at the top of the diagram at apex 3. The molar ratios of the two pseudo-components along each dilution line are then defined by entering the mole fraction of pseudo-component B for each desired line in the table under Dilution Line Definition. The number of flashes desired on each dilution line must also be specified. On Tab Ref. State, the following information is entered: Calculation Method Identifier The three-phase flash algorithm performs flash and stability calculations in an alternating sequence. The calculation begins with a stability test on the single-phase fluid. If the phase is unstable, a two-phase flash calculation is performed, followed by a stability test on the converged two-phase system and so on. Three calculation methods are available. They differ in the sequence in which the stability tests are performed. In Method 1, the stability test is performed first with respect to the solid phase. In Method 2 (default), the stability test is performed with respect to all fluid phases prior to a stability test with respect to the solid phase. Method 3 is a special case of Method 1; with Method 3, a stability test on the converged twophase fluid-solid system is not performed. Thus, Method 3 is more efficient but not as rigorous as Method 1. For most cases, Methods 1 and 2 converge to the same results. In exceptional cases, it has been found that only one method converged while the other one failed.
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Number of Solid Forming Components Of the Nc total components, the user may specify the last N1 as the number of solid forming components. The default is set to 1, that is only component number Nc can precipitate. Once this number is specified in the text box provided, the component number and name for all the precipitating components are shown on the first and second columns of the table on this tab. Depending on the method selected for computing the reference fugacity, columns 3-5 of this table will also be updated automatically. Reference Fugacity (ln (solid fugacity (atm))) Four options are available for specifying the reference fugacity through the Reference fugacity combo box: CALCULATE
LCORRELATE
PREVIOUS USER INPUT
The reference fugacity at the specified pressure and temperature is set equal to the fugacity of the solid forming component after the system has converged to a single liquid phase or a two-phase vapor-liquid system. This is used for wax only. The reference fugacity at the specified pressure and temperature will be correlated with the pure component liquid fugacity at the same pressure and temperature. Use the value for the reference fugacity from a previous multiphase solid flash calculation. This selection implies that the value of the natural logarithm of the reference fugacity in units of atmospheres as well as the corresponding reference pressure and temperature will be input by the user for each precipitating component on the table provided. The user must select this option before the values can be entered in the table
If the reference fugacity specification is set to CALCULATE, solid onset pressures for the same mixture but at different temperatures may be specified in the Additional Onset Points table. ΔCp and ΔHtp (optionally vs) can be calculated so the solid model will match these onset points. Additional Onset Points Solid onset pressures at different temperatures may be used to calculate parameters in the solid model for performing temperature-dependent precipitation predictions. The requirements for doing this calculation are: • Two, three or four solid precipitation onset pressures at different temperatures must be known for one fluid composition. • The solid phase must be modelled with a single component, as is normally done for asphaltene precipitation modelling. The pressure and temperature for one of the onset points must be entered on the Calculations tab as the pressure and temperature for the flash. This will be used as the reference condition, and will define the reference fugacity. Calculation of the other parameters will depend on the number of additional onset points entered, as described below. Normally vs is adjusted to match a known amount of solid at a given condition (bulk precipitation experiment) otherwise it will default as described under Solid-Phase Molar Volume.
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• 1 additional onset point – ΔCp is set to the user-input value or defaults to zero. ΔHtp is calculated to match the specified onset point. • 2 additional onset points – ΔCp and ΔHtp are calculated to match the specified onset points. • 3 additional onset points – ΔCp, ΔHtp and vs are calculated to match the specified onset points. This is not normally done, as it is preferable to use vs to match a bulk precipitation experiment. Reference Pressure (psia | kPa | kg/cm2) This corresponds to the reference pressure for calculating reference fugacity. This pressure is required only if a reference fugacity is actually entered. If Field units is selected enter value in psia, for SI units in kPa and for modified SI units in kg/cm2. When the CALCULATE, PREVIOUS or LCORRELATE options are selected for the reference fugacity, the reference pressure is set internally by the program and need not be entered on the table. Reference Temperature (°C for SI or °F for field units) This corresponds to the reference temperature for calculating the reference fugacity. This temperature is required only if a reference fugacity is actually entered. When the CALCULATE, PREVIOUS or LCORRELATE options are selected for the reference fugacity, the reference temperature is set to appropriate values internally by the program and need not be entered on the table. Solid-Phase Molar Volume (l/mol) This corresponds to the component solid-phase molar volume for the calculation of the component solid-phase fugacity. If the molar volume is not specified, the following value is assigned: •
If the reference fugacity option is CALCULATE, the solid-phase molar volume is calculated from the EOS, unless 3 additional onset points have been specified.
•
If the reference fugacity option is LCORRELATE then the molar volume is obtained from a correlation by Won (1986).
•
If the reference fugacity option is PREVIOUS, the solid-phase molar volume from the previous calculation is used.
•
If a value for the reference fugacity is entered, the solid-phase molar volume is calculated from the EOS.
Heat Capacity (cal/K/mol) This corresponds to the component solid-liquid heat capacity difference for calculation of the component solid-phase fugacity. If this quantity is not explicitly specified for each precipitating component, the following value is assigned: •
If the reference fugacity option is CALCULATE, the solid-liquid heat capacity difference defaults to zero, unless 2 or more additional onset points have been specified.
•
If the reference fugacity option is LCORRELATE then the heat capacity difference is obtained from a correlation by Pedersen (1991).
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•
If the reference fugacity option is PREVIOUS, the solid-liquid heat capacity difference from the previous calculation is used.
•
If a value for the reference fugacity is entered, the solid-liquid heat capacity difference defaults to zero.
Heat of Fusion (cal/mol) This corresponds to the component heat of fusion for the calculation of the component solidphase fugacity. If this quantity is not explicitly specified for each precipitating component, the values are obtained from a correlation by Won (1986). Triple Point Pressure (psia | kPa | kg/cm2) If the triple point pressure for each precipitating component is known then these may be specified under the column heading Triple Pres. If Field units is selected enter value in psia, for SI units in kPa and for modified SI units in kg/cm2. If the triple point pressure is not known then the default is a value of zero, which is realistic for high molecular weight compounds. Triple Point Temperature (°C for SI or °F for field units) If the triple point temperature for each precipitating component is known then these may be specified under the column heading Triple Temp. If not known then the values are estimated from an internal correlation that was developed by Won (1986). Ratio of reverse over forward rate for conversion to irreversible solid This is the equilibrium constant “K” described above under “Irreversible Asphaltene Calculations”.
Single-Phase Calculation A flash calculation in the single-phase region yields a single-phase system. However, if the fluid is known a priori to be single phase, its properties can be calculated directly with the single-phase calculation option. This option is invoked by selecting Calculations|Singlephase Fluid. Please be advised that WinProp will assume single-phase for all calculations even if the fluid is multiphase. An example data set for this option is singlephase.dat.
Isenthalpic Flash Calculations Theoretical Background Isenthalpic flash calculations correspond to finding the temperature, phase splits (phase mole fractions) and phase compositions, given the pressure, composition and enthalpy of the feed, together with the net enthalpy added to the system (Agarwal et al, 1988). For isenthalpic flash calculations, in addition to the material and phase equilibrium relations applicable to isothermal flash calculations, there is an energy balance equation, i.e. np
nc
j =1
i =1
(
)
g n p ≡ H − H spec = ∑ Fj ∑ y ij h ij − H spec = 0
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where Hspec is the specified molar enthalpy of the system and hij is the partial molar enthalpy of Component i in Phase j which is also obtained from an EOS. Calculation Method Identifier Two schemes for isenthalpic flash calculations are discussed below. The final scheme is a hybrid of these two schemes. Scheme 1 Scheme 1 consists of performing a series of multiphase isothermal flash calculations by adjusting the temperature to satisfy the energy equation. In other words, the temperature is varied in an outer loop, and the isothermal flash equations are solved in an inner loop. Techniques for solving the multiphase isothermal flash equations are taken from Nghiem and Li (1984) and Nghiem et al (1985). The isenthalpic flash calculations are initiated by an isothermal flash calculation at the specified feed composition z, the specified pressure p and an initial guess for temperature, T(0). A new temperature T(1) is then determined from the energy equation by assuming that the phase mole fractions, compositions and specific enthalpies are constant. With T(0) and T(1), a secant method for solving the energy equation is set up in the outer loop. As discussed later, Scheme 1 does not work for systems with a degree of freedom equal to unity, e.g. one-component two-phase system, two-component three-phase system. Scheme 2 Scheme 2 basically follows Michelsen's approach (Michelsen, 1987), but the implementation is different. This scheme is a stage wise procedure where the system is assumed to be initially single-phase, and where the number of phases is increased if necessary between iterations. Furthermore, this scheme attempts to converge the material balance equation, the energy balance equation and the equilibrium equation in a sequential manner. This method also works for systems with a degree of freedom equal to unity. Special Considerations Isenthalpic flash calculations are more complex than isothermal flash calculations because of the lack of the a priori knowledge of temperature (and phases) and because of the presence of narrow boiling mixtures. The implications of these two factors are discussed in the following. Phase Information Since temperature is not known a priori in isenthalpic flash calculations, the traditional stability analysis of the Gibb's free-energy surface (Nghiem and Li, 1984) cannot be used to determine the number of phases that actually exist at convergence. A stability analysis can only give the number of phases at the initial temperature estimate, which may not be the same as the number of phases at convergence. This leads to the appearance and disappearance of phases during the iterative process. This does not create any difficulties for Scheme 1 but could cause convergence problems for Scheme 2. Narrow-Boiling Systems Narrow-boiling systems are those where the enthalpy changes drastically for a small change in temperature during phase transition. Although many multicomponent fluids exhibit this behavior, a single-component fluid in the two-phase region and two-component fluid in the three-phase region are extreme examples of narrow-boiling mixtures. User's Guide WinProp
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From the phase rule, the degree of freedom F of a system with nc components and np phases is F = nc+ 2 - np Thus for a single-component system in the two-phase region, F = 1. This implies that, if the pressure is fixed, the two-phase temperature is also fixed. In other words, pressure and temperature are dependent on each other in the two-phase region. The enthalpy for this system is determined by the phase split in the two-phase region. The same analysis applies to a two-component system in the three-phase region. Effect of Narrow-Boiling Systems on the Calculations Scheme 1 is not applicable to systems with a degree of freedom equal to unity (e.g. onecomponent two-phase systems, two-component three-phase systems) because it attempts to satisfy the energy equation by adjusting the temperature. For these systems, the energy equation can only be satisfied by adjusting the phase split. Otherwise, Scheme 1 works for any multicomponent systems with nc ≥ 3 even if they exhibit narrow-boiling behavior. Calculation Procedures A hybrid scheme, where five scheme-2 iterations are performed for every scheme-1 iteration, is very stable and robust. Of course, only Scheme-2 is used for one and two component systems.
Input Data - Isenthalpic Flash Add this option to your data set by selecting Calculations|Isenthalpic Flash. A number of examples are provided in the template test bed. These cases are named flash-isenth1.dat through flash-isenth3.dat and can be found under the template (.tpl) directory. For Feed, Kvalues, Output level and Stability test level specifications, see the Chapter “Common Data Required for all Options”. Flash calculations are performed at the pressure specified in the Text Box labeled Pressure. Enter a value for the enthalpy in the text box labelled Enthalpy. In the Text Box labeled Temperature, enter an initial guess for the temperature. This initial guess for the temperature is required input and must be specified by the user. Calculation Method Identifier As detailed above under the calculation method identifier section of the theoretical discussion, two methods are implemented to solve the nonlinear set of equations corresponding to isenthalpic flash. A hybrid scheme where five scheme-2 iterations are performed for every scheme-1 iteration is very stable and robust and is the default choice. The integer number entered in the text box labeled Calculation Model indicates the number of iterations of scheme 2 to be used for every iteration of scheme 1. A value of zero therefore implies the selection of Scheme1 exclusively. A value equal to or greater than 101 will be interpreted as the selection of Scheme 2 alone.
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Three-Phase Boundary Calculation
Background For systems that exhibit three-phase behavior, there exist conditions where one of the phase mole fractions goes to zero. Under these conditions, there are two phases in equilibrium with an infinitesimal amount of a third phase. The locus of all these conditions corresponds to a three-phase boundary. Nghiem and Li [21] describe calculation techniques for constructing the three-phase boundary; these are extensions of the two-phase boundary calculations described in a separate chapter. You can calculate the following envelopes: •
Pressure-Temperature (PT) diagram
•
Pressure-Composition (PX) diagram
•
Temperature-Composition (TX) diagram
Input Data The three-phase boundary calculation is invoked by selecting Calculations|Three-phase Envelope. Examples of three-phase PT envelope and PX envelope are in envel_3ph-pt.dat and envel_3ph-px.dat respectively. This calculation requires good initial guesses for convergence. Therefore the pressure, temperature, and K-values must be obtained from a previous three-phase flash calculation near the boundary as in envel_3ph-pt.dat, or entered by the user as in envel_3ph-px.dat.
Envelope Specification Tab Specify the type of envelope (PT, PX, or TX) to be calculated by selecting the variables for the x- and y-axes on this tab. For the PT diagram the composition is fixed. The composition is determined based on the data entered on the form Composition and the feed specification entered on Tab Feed/Output/Stability. For the PT envelope, also specify the first point to be calculated by entering a value for the x-variable and an estimate for the y-variable in the combo boxes labelled Pressure and Temperature respectively. The x-variable and y-variable are also called independent and dependent variables respectively. The choices for the combo box for the y-variable are: Previous, or enter a value explicitly. For PX and TX diagrams the composition changes as the envelope is traversed. The x-axis variable in these cases is the mole fraction of the secondary fluid. The initial value of this mole fraction is as defined by the feed specification. For the PX diagram, enter the initial guess for the pressure in the combo box labelled Pressure. Also enter a value for the temperature (fixed) in the combo box labelled Temperature.
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Similarly for the TX diagram, enter an initial guess for the temperature in the combo box labelled Temperature and a value for the pressure (fixed) in the combo box labelled Pressure. For all cases an initial guess for the mole fraction of either the vapor phase or the second (intermediate) liquid phase is also required. For the boundary corresponding to zero vapor phase, enter a value for the “second liquid” or intermediate phase mole fraction. For the boundary corresponding to zero second liquid phase, enter a value for the vapor phase mole fraction initial guess. If Use values from previous calculations is selected, WinProp will calculate the boundary corresponding to the phase with the lowest mole fraction (in the previous calculation) equal to zero. Defaults for the maximum and minimum values for the x- and y-variables can be overridden by entering values in the appropriate text boxes. The calculations stop when the maximum or minimum values are exceeded or when the maximum number of points has been calculated (see Envelope Construction Controls Tab). The calculations will also stop if the mole fraction of any phase falls outside the limits specified by the values in the text boxes Minimum phase mole frac and Maximum phase mole frac. The default values of –10 and 10 for the minimum and maximum are chosen such that the calculation will not stop unless large non-physical values of the phase mole fractions are encountered. The Tab Envelope Specification corresponding to envel_3ph-px.dat is shown below:
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Envelope Construction Controls Tab
Maximum Number of Points This value corresponds to the maximum number of points calculated on the phase diagram. Initial Step Size The Initial step size controls the spacing between the calculated points on the envelope. Both positive and negative values may be used. For positive values, the diagram is traced initially in the direction of increasing x-values. For negative values, the diagram is initially traced in the direction of decreasing x-values. WinProp internally estimates the step size for subsequent points on the envelope. Average Number of Iterations This value is used to adjust the distance between two consecutive points on the diagram. The distance is increased if the actual number of iterations is less than the entered values, and is decreased in the opposite case. Independent Variable Interpolation Points These correspond to x-values for which you want calculated y-values. Because the step size in the envelope calculation is automatic, these interpolation values must be entered to force calculations at desired x-axis values.
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Initial K-Values Tab
The estimates of the K-values for the first point on the boundary can be from a previous calculation, or entered in the appropriate table as shown in the above figure.
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Component Splitting and Lumping
Overview Our experience shows that two representations of the components are normally required in the modelling of the phase behavior of reservoir fluids. In the first stage, the fluid system is represented by a large number of components (e.g. C1, C2, C3, ..., C29, C30+). Simple calculations such as saturation pressure calculations are performed on this many-component system to verify the adequacy of the EOS. We found that in most cases the EOS can predict accurately the saturation pressure with only minor adjustment to the Hydrocarbon Interaction Coefficient Exponent (HICE). See the chapter entitled “Regression” for more details. This many-component representation is not practical for compositional simulation because of the excessive run time and memory requirements. The second stage involves the lumping of the many-component system into fewer components (e.g. 10). Reservoir fluids typically consist of pure, well-defined components such as CO2, N2, C1, C2, etc., and many hundreds of heptanes and heavier components (C7+). The laboratory analysis of a reservoir fluid includes generally a gas chromatograph analysis of the C7+ fraction into Single Carbon Number (SCN) fractions up to C30+ for example. Characterization of the C7+ fraction as a number of pseudo-components is accomplished using WinProp’s Plus Fraction Splitting and Component Lumping calculation options. If a full extended analysis is available with mole fraction, MW and SG or Tb given for each SCN fraction, the SCNs may be entered as user components directly on the Component Selection/Properties form. If a complete analysis is not available, the Plus Fraction Splitting calculation is used to define a distribution function relating mole fractions to molecular weights of the C7+ fraction. Three distribution functions are available in WinProp: exponential, two-stage exponential, and gamma distribution. The implementation of the distribution functions depends on the experimental data available. If a partial extended analysis is given (e.g. only MW and mole fraction of the SCN fractions) and one of the exponential distribution types is selected, the splitting calculation does not use the distribution function. SG and Tb values for the SCN fractions are determined from correlations based on the SG and MW of the plus fraction. Subsequently, critical properties of the SCNs may be generated. After the splitting, the SCNs representing the C7+ fraction can be lumped into fewer components based on K-values estimated from Wilson's correlation using the Lee-Kesler mixing rules, (Lee and Kesler [15]).
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If a partial extended analysis is given and the gamma distribution is selected, the α parameter in the distribution is determined by minimization to obtain the best fit of the distribution to the experimental data. At this point, the analysis may be extended by using the distribution function to generate mole fraction and molecular weight data for SCNs beyond the last fraction in the experimental analysis. SG, Tb and critical properties of the SCNs may be generated and lumping to fewer components may be done as for the exponential distribution case. Alternatively, the gaussian quadrature technique may be used to determine MW and mole fractions of the pseudo-components from the distribution function. Correlations are then used to generate the SG, Tb and critical properties of the pseudo-components directly, rather than using mixing rules. If no extended analysis is available, i.e. only mole fraction, SG and MW of the C7+ fraction are known, the parameters in the chosen distribution function are adjusted to match the known data. The distribution function is then used to generate SCN mole fraction and MW. Once this is done, the characterization may proceed as described for the partial extended analysis cases above. Due to the larger number of adjustable parameters in the gamma distribution, the α parameter must be specified if no extended analysis is available. If it is not input by the user, the program will estimate a value for this parameter. The Component Lumping calculation may be specified in a data set if the SCNs were not lumped within a splitting calculation, or to further reduce the number of components. The lumping scheme may be input by the user, or the program can generate the pseudocomponents using an internal algorithm. We recommend specifying a lumping scheme based on the K-values of the many-component system at a prevailing condition in the reservoir, e.g. the saturation condition.
Characterization of Multiple Related Samples Multiple related samples can be characterized using the gamma distribution and gaussian quadrature techniques as described by Whitson et al [40]. This results in a single set of C7+ fraction pseudo-components for all samples. Plus fraction MW and SG for each sample are matched by determining the correct mole fractions of each pseudo-component for the sample. Data for each sample is entered in exactly the same manner as for single sample characterization. The same type of data need not be entered for each sample; i.e. an extended analysis may be entered for one sample and only plus fraction SG, MW and mole fraction for another sample.
Splitting the "Plus" Fraction This option is invoked be selecting Characterization|Plus Fraction Splitting. An example data set for this option is split-mwsg_plus.dat. General splitting model controls are entered on Tab General of the Plus Fraction Splitting calculation form as described below.
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User's Guide WinProp
Distribution Function Type Three choices are available for the distribution function for splitting the plus fraction: Exponential
Exponentially decreasing function appropriate for gas condensates and lighter fluids
2-Stage Exponential
Approximation to the gamma function suitable for black oil type fluids
Gamma
Three-parameter gamma distribution suitable for all fluid types
Number of Fluid Samples If the gamma distribution is chosen, up to 8 related fluid samples may be characterized simultaneously. If the exponential distributions are chosen, this text box is not enabled. First Single Carbon Number in Plus Fraction Enter the carbon number of the lightest SCN in the plus fraction (e.g. enter 6 to characterize a C6+ fluid fraction). Number of Pseudo-Components The SCNs can be used as is in subsequent calculations or lumped into pseudo-components right after the splitting procedure. The following options are available: No lumping
The SCNs will be used as is.
Determined internally
WinProp will estimate internally the number of pseudocomponents for the plus fraction.
Input value
Specify the desired number of pseudo-components.
When using the gamma distribution and gaussian quadrature without extended analysis, the number of pseudo-components cannot be estimated via correlation and will be set equal to 3. Lumping Method Log(K) lumping is available when characterizing a single sample with any of the distribution functions. Gaussian quadrature lumping may be used with the gamma distribution, and is required for characterizing multiple samples. Log(K) lumping defines pseudo-components as having equal ranges of log(K). Gaussian quadrature lumping defines pseudo-components via analytical integration of the gamma distribution. Critical Properties Correlation Three correlations are available to calculate the critical properties of the SCNs. 1. Lee-Kesler (Kesler and Lee [12]) 2. Riazi (Riazi and Daubert [34]) 3. Twu (Twu [36]) On the Distribution Tab, parameters relating to the chosen distribution are entered. Three of these properties are common to both exponential and gamma distribution types, as follows.
User's Guide WinProp
Component Splitting and Lumping • 79
SCN Fraction MW Interval This corresponds to the interval in molecular weight for each single carbon number group. For the gamma distribution, if a variable MW is selected this value is ignored. The default is 14.026. “Bias” Parameter for SCN MW End Points This parameter is used for setting the minimum molecular weight for the plus fraction distribution. A value of 0 means that the minimum MW will be equal to the normal alkane MW of the same carbon number as the first SCN fraction in the plus fraction. A value of 1 means that the minimum MW will be equal to the normal alkane MW of one lower carbon number than the first SCN fraction in the plus fraction. The default value is 0.75. Distribution Function Cutoff This parameter is used in determining the number of pseudo-components for lumping. This calculation requires specification of a maximum SCN number. Setting the cutoff to 1.0 means that the maximum SCN number will be set equal to the last SCN number in the analysis. This often leads to over-prediction of the required number of pseudo-components. Setting the cutoff less than 1.0 indicates that the maximum SCN number will be taken as the one at which the ratio of the sum of the individual SCN mole fractions to the total plus fraction mole fraction exceeds the cutoff. The value should be less than 1. The default is 0.95. Parameters specific to the exponential distributions are: Mole Fraction of Component Preceding Plus Fraction This value is used to set the “Y-Axis” intercept of the two-stage exponential distribution function. For C6+ fraction characterization, this value should be set equal to the mole fraction of the C5 components, for C7+ fraction characterization, this value should be set equal to the mole fraction of the C6 components, etc. “Y” Axis Intercept of the Distribution Function This is usually set equal to the mole fraction of the component preceding the plus fraction (default). Parameters specific to the gamma distribution are: SCN MW Interval Type When fitting the gamma distribution to extended analysis data, the SCN fractions can have fixed or variable intervals in molecular weight. Choosing Constant sets the MW interval equal to the value entered under SCN fraction MW interval. Choosing Variable (match mole fraction) or Variable (match weight fraction) indicates that the upper MW boundary of the SCN fraction is varied until either the experimental mole fraction or the experimental weight fraction (default) of the SCN is matched. Eta Parameter (Minimum MW in Distribution) The eta (η) parameter specifies the minimum molecular weight in the gamma distribution. By default, it will be calculated as described under “Bias” parameter for SCN MW end points.
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User's Guide WinProp
MW of Heaviest Pseudo-Component The choices for molecular weight of the heaviest pseudo-component are No Restriction, Internal Default or entering a value. Specifying No Restriction implies no upper limit in MW on the gamma distribution, and is not recommended. It leads to prediction of very high molecular weights for the heaviest pseudo-component. The default setting obtained by selecting Internal Default sets the heaviest pseudo-component MW equal to 2.5 times the MW of the plus fraction. If multiple samples are used and No Restriction is selected, it will automatically be reset to Internal Default. SG-Tb-MW Correlation When Gaussian quadrature is used with the gamma distribution, the following correlations are available for determining pseudo-component boiling point from specific gravity and molecular weight. 1. Twu (Twu [36]) 2. Goossens (Goossens [7]) 3. Riazi (Riazi and Daubert [34]) The controls available for determining gamma distribution parameters by minimization are: Residual Value The choices for residual value depend on what is selected under SCN MW interval type. The residual value setting indicates what experimental data for each SCN is used in defining the error function to be minimized. The choices are Molecular Weight, Mole Fraction and Weight Fraction. If a constant MW interval is chosen, then molecular weight is not available as a choice of residual value. Similarly, if a variable MW interval is chosen to match the mole fraction, then mole fraction is not available as a choice of residual value. The default is to vary the MW interval to match the weight fraction of the SCN, and adjust the distribution α parameter to minimize the error function defined in terms of the molecular weights. Residual Type The choices for residual type are Sum of Squares, Chi Square Goodness-of-Fit Test or Sum of Scaled Squares. The default is sum of squares. For most applications, the difference in minimization results between the residual types will be small. Final SCN Fraction Data The residual calculation can be specified to include or not include the data from the final SCN fraction in the analysis. On each Sample Tab, the properties of the plus fraction are entered. The number of sample tabs appearing is set according to the Number of Fluid Samples entered on the General tab. If extended analysis data is available from a true or simulated boiling point (distillation) analysis, the data can be entered in the table on the Sample tab. In column 2 enter the mole fraction of each fraction. In column 3 enter the average molecular weight of the fraction. Note that if any extended analysis data are to be entered, mole fraction and molecular weight are required for each cut. If data is available then values for the specific gravity can be entered in column 4 and normal boiling point in °C in column 5. Please note that if data for normal boiling point is
User's Guide WinProp
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entered then data for specific gravity must also be entered. Sample data sets with extended analysis data are split-mw_analysis, split-mwsg_analysis and split-mwsgtb_analysis. Number of SCN Fractions If this entry is left blank, the value will default to the number of fractions in the analysis, or to 25 if there is no extended analysis. If the exponential distributions are used with extended analysis, and a value for number of SCN fractions is entered, it will be ignored. If the gamma distribution is used with extended analysis, and a value for number of SCN fractions is entered that is greater than the number of fractions in the analysis, the analysis will be extended using the distribution function to the specified SCN number. MW+ Molecular weight of the plus fraction must be entered in the text box unless extended analysis data is given. SG+ Specific gravity of the plus fraction must be entered in the text box unless SG data is given in the extended analysis table. Z+ Mole fraction of the plus fraction must be entered in the text box unless extended analysis data is given. If one of the exponential distribution function types is selected then the following data entry box will be available: Slope This is the slope of the exponentially decreasing curve of the distribution function. If not specified then it is determined internally based on data for a typical oil. If the gamma distribution function is selected then the following data entry box will be available: Alpha This parameter is analogous to the slope parameter used for the exponential distribution types. If α>1, the distribution has a peak in mole fraction for an SCN greater than the initial SCN in the distribution. If α=1, the gamma distribution reduces to an exponential distribution, and if α
