Olga - Start

INFORMATION FOR  BEGINNING WITH OLGA Plan of this page :

1. Presentation of Olga Scandpower  Software 2. First steps with Olga 3. Some advises about the GUI 4. Some advises about the PVT file 5. General advises

Presentation of Olga Scandpower Software Olga is a Norwegian petroleum software originally developed b y IFE for Statoil in 1983. Olga 2000 is capable of one dimensional simulation of Oil, gas and water flows. You can find information about the Olga model in The dynamic Two-Fluid Model Olga: Theory and application  by Bendiksen, K.H Malnes, D. Moe, R. and S. Nuland edited by SPE Production Engineering, May 1991, pp. 171-180. Olga is supposed to can be used for:        

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Oil and Natural gas flowlines or transportation lines, Wet gas or condensate pipelines, Well stream from a reservoir, LNG / LPG/ NLG pipelines, Dense phase pipelines,  Network of merging pipelines, Artificial lift and other mass source injections, inje ctions, Pipelines with process equipment ( compressor, heat exchanger, separators, check -valve, controller, mass source / sink), Single phase gas or liquid, Small diameter pipelines with various fluids, Laboratory experiments.

The input system of Olga consists in six files. Input file 1 & 2 are always required while 3,4,5 & 6 are optional. File 1 (name.inp): General case definition: name, reference, geometry, ope rational conditions, output variables File 2 (name.tab): Fluids properties definition ( also called PVT file ) Files 3, 4, 5 & 6: Optional files for compressor, pump & restart file. The version I used is an Olga Graphic User Interface (GUI) version called Olga 2000. The GUI allows the user to :   

create the files 1, 3, 4, 5 & 6 directly via several modules (keywords), draw graphs, verify the TXV file (Fluid Properties button),

In a nutshell, the GUI simplifies considerably the using of Olga in defining the case in some windows and not in a text editor. Besides, even if you have an Olga GUI version, you can complete directly the files in a text editor of your choice (it also allow the user to control what he enters in the interface). Moreover, the GUI propose you two ways of launching the calculus : a  batch version or a interactive version (in which you can reduce the time of your simulation without changing the file).

First steps with Olga How getting help To found help, refer to the two written manuals of Olga 2000 ( User's Manual for global information about Olga & Getting Started for the GUI using) or click on help directly under  Olga, then you will access to the HTML version of User's Manual. You can also contact directly Scandpower. How beginning To begin with Olga, I recommend you look the Olga examples (at the end of the User's Manual, appendix C to O). Personally, I used the first example (appendix C) to un derstand how to implement the Olga files. First, I opened this case and saw how to draw graphs. Then, I opened the different modules of the GUI version of the ca se main file (click on 'show Keyword' to have a direct access to these modules) . And then, I tried to reproduced the same case under the Olga GUI. In that way, I understood how to enter the case and when I encountered problems, I opened the .inp file (case file) to see really what I had entered. In that way, I understood how to select an item in a list, how to enter different values in a same line (as example, different times), how to draw graphs and how to access to the modules I want to implement.

Then to implement networks of pipes, I used the second example (appendix D). In the following section, I give some advises relative to the major problems I encountered.

Some advises about the Olga GUI The Graphic User Interface of Olga is quite simple to take into hands but I encountered some difficulties to enter some values in the different modules. Click HERE to see the GUI

Thanks to the GUI, you can directly:   

Launch the calculus, Create the case files (but not the PVT), Draw graphs (Trend or Profile).

Following some advises about problems I encountered. Founding the divers modules of the files To use correctly the Olga GUI, you have to press the 'keywords' button. In that way, all the basic modules you have to complete would appear. For the other modules, you can enter into a modules and press next until the desired module appears or (better) directly select the desire module via the upper tools bar, section Keywords . Entering divers values in a same line It is simple but I encountered some difficulties the first time I went to enter different time values. As example, I want to enter a mass flux time dependant. I enter three time values: at t = 0 s, t = 20.5 s and t = 40 s. I have to enter in the time line : 0.0 , 20.5 , 40 (without the parentheses, but they will be added in the text version of the file). For the other lines of the module, you have to enter 3 values of the property corresponding to the different times (always without parentheses). Remark: If Olga does not agree with your values, they will disappear instantaneously with a 'bip'. Selecting an item in a list (as example the pipe or branch ...) This is also simple but the first time it can be problematic. In fact, you cannot directly enter the name of your item, you have to select it on a list. When you have to select an item in a list, a special button is put at the end of the line. It is a rectangular button with three points or with a a rrow pointing down. Press this button to obtain the list. Then select the item and click on replace (if this button appears). Avoiding the GUI Sometimes, the GUI refuses a value (this value disappear and you can hear a 'bip').

It can be because your value is not correct: you have entered divers time values so you have to enter a list for this line. If you think to ha ve right, do not hesitate to open the .inp file in a text editor. In that way, you can verify your case and change what you want. Click HERE to see the GUI

Some advises about the PVT file In this file, the divers properties of the fluids are defined. There is a tool to help the user to create this file but I do not have it at my disposal. So I created my own PVT file directly in a text editor. To have a referenced, I opened an Olga PVT file example (Ol-terslug-1.tab) and with the manual, I changed it to adapt it to my case. Consequently, if you have to do the same or to read such a file I can give you some advises relative to my case.  

In the first line, between quota, a code is written to identify the fluids. In the second line, enter the number of, respectively, pressure and temperature steps you want to define:  NbP NbT

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In the third line, enter respectively the pressure and temperature steps (in bar and degree Celsius): DeltaP DeltaT

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In the fourth line, enter the 'initial' point: initial pressure (in bar) and initial temperature (in degree Celcius) Po To

In that way, you will defined the properties of your fluids in NbP * NbT points: P between Po and Po + deltaP * (NbP 1) T between To and To + deltaT * (NbT 1) 

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In the fifth and sixth lines, enter NbT numbe rs. Personally, I do not know what they represent and I let the numbers I found in the Olga example. Then, you will have to write a keyword representing a property of the liquid or gaseous  phase. Below this keyword, you will have to give the value of this property at each  points. You will write NbP lines of NbT values. You can consider that as a matrix. In the

line i and column j, you will write the value at Po + deltaP * (i - 1) bar and To + deltaT * (j - 1) degree celcius.

Two other advises : 

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If you go to the help section of your manual about the second file (name.tab), you will see that some keywords do not correspond to the manual. In fact, in this file, as example, the evolution of the the volumic mass of the gas function of the temperature is represented by the keyword drogdt. Generally, you can assume that the gaseous phase is perfect and its density verifies the following equation:

General Advises Incomprehensible error message Olga functions under Windows and both are unstable . Consequently, do not hesitate to close your case and reopen it to launch it if you have an error stating that you have no license or that the application is busy. Besides, if you close the Olga deamon then you have to reopen it to launch simulation in the Execution control mode. Debugging To debug your case, you can use the batch execution mode (run batch): it would write step by step the errors it encountered in your files. In that mode you can also launch the debugger of  Olga (it will underline the non physical aspect of your case), you have only to select 'on' in the case OPTIONS module in front of DEBUG (ke yword = ' OPTIONS'). Be simple at the beginning Personally, at the beginning, I only used the examples 1 and 2 of the Olga manual. With these examples, I simulated a vertical pipe and a network of pipes with one manifold for four wells. I only used sources to introduce flows. I introduce a valve but without checkvalve. In fact, I only create and use the principal files of Olga but not the equipment files. Simulation of a steady state Personally, I simulated steady state via launching the simulation for 20 or 5 seconds. In that way, the calculus converged to the steady state. Flows entry conditions With Olga, you have to enter the total mass flow rate (Qt) and the gas fraction (Gfraction). These quantities can be understand via the following formulas:

J is the surface velocity, Q the mass flow rate, S the surface of the section and rho the density.

The values keywords To edit value (via Trend, Profile or Output modules), you have to define them with their  keywords. As example :    

to edit the flow regime indicator, use ID, to access to the void fraction, write AL, to edit jg (the gas velocity or gas flux), enter USG, to edit the pressure, enter PT...

All these keywords are given at the end of the Olga principal manual. The output file You can visualize your results directly with the GUI (Trend or P rofile sections) but you can also write the results in a text file with a .out extension. You can open this file in a text editor ( like Wordpad ). You can use the Output section of the .inp file to determine the values you want to write (with the keyword given in annexes). In the .out file, you will read the .inp file and the output results you have implemented in the Output section. You can also open this file with Excel and draw your own graphs. It is very interesting to open this file becau se you will discover  what is really implemented in your case (in particular, you will see that some values are taken in the center of the cells and some other in the limits of the cells).