CLASS Reservoir Simulation

RESERVOIR SIMULATION •The will discuss all of the important facets of the reservoir modeling process. • Important factors that can dramatically impact the model results are emphasized. •Specific topics include Data Acquisition, Fluid Properties, Rock-Fluid Interaction, Grid Construction, History Matching and Prediction Cases. •These and other topics will help the attendees better understand how to plan and conduct a reservoir simulation study and how to review a study conducted by someone else. •Although there will be no direct computer related activities, time throughout the two-days is reserved for discussion of case studies that were previously models conducted by the teacher. •Attendees are also encouraged to bring materials and data (non-confidential) relating to a potential project that they may be involved with in the future; and as time permits, the class as a group (or groups, guided by the teacher) will brainstorm and discuss the approach to be taken to achieve the desired study objectives.

Syllabus Course Topics Covered within the Course • Introduction • General Overview • Theory of Numerical Simulation • Planning a Simulation Study • Data Acquisition and Analysis • Fluid Properties • Rock-Fluid Interaction Relationships • Geologic Model Development • Grid Construction · Grid Features and Other Issues • Model Initialization • Well History • History Match • Prediction Cases • Review of Simulation Models · Use of Simulation / Reserves • Summary • Examples/Case Studies

Grading Homework and project: Exam: Class contribution:

40% (8 practices) 50% (Partial, final) 10%

Why We Do Reservoir Simulation Typical Problems • How many wells • What rate • Infill Drilling • Perforation • Work-over • Pressure Maintenance • Water or Gas Injection • Pattern Flood

Reservoir Drive Mechanisms

1. 2. 3. 4. 5. 6.

Rock and fluid expansion Solution-gas drive Gas-cap drive Water drive Gravity-drainage drive Combination drive

12/19/2012

Maximizing Oil Recovery

4

Solution Gas Drive

Liberation, expansion of solution gas.

12/19/2012

Maximizing Oil Recovery

5

Solution Gas Drive (Cont.) Typical Production Characteristics

12/19/2012

Maximizing Oil Recovery

6

Solution Gas Drive (Cont.) Reservoir pressure trend

12/19/2012

Maximizing Oil Recovery

7

Gas Cap Drive Expansion of the original reservoir free gas.

12/19/2012

Maximizing Oil Recovery

8

Gas Cap Drive (Cont.) Typical Production Characteristics

12/19/2012

Maximizing Oil Recovery

9

Water Drive



Influx of aquifer water

Types : Edge-Water

12/19/2012

Bottom-Water

Maximizing Oil Recovery

10

Water Drive (Cont.)  Typical Production Characteristics

12/19/2012

Maximizing Oil Recovery

11

Gravity Drainage Gravitational forces and reservoir fluids density difference.

12/19/2012

Maximizing Oil Recovery

12

Combination Drive

12/19/2012

Maximizing Oil Recovery

13

Average Recovery Factors

12/19/2012

Maximizing Oil Recovery

14

SIMULATION: "To Give the Appearance Of…”

Reservoir Simulation

Engineering/Simulation Model 106-108 cells

Outlines • Brief of simulation • Introduction of Eclipse • Eclipse demo

Brief of simulation What is simulation? Imitation or representation, as of a potential situation or in experimental testing What would be simulated usually?

What is Reservoir?



Trapped HC, same pressure gradient

Tops Boundary

Layer zone

Faults

How to know and understand a reservoir?

lithological

sandstone grades to clay sediment

GAS OIL WATER

sandstone pinch out

What we shall know from a well?

• Lithology (reservoir rock?) • Resistivity (HC,water,both?) • Porosity (how much HC?) • What type of HC • Formation mech. properties • Permeability / cap pressure • Shape of the structure • Geological information • Geothermal

How to describe reservoir? Formation

Fluid Property

Tops Layer Zone Dz (Thickness) Dznet (Net Thickness) Faults Boundary Permeability Porosity

Relative permeability Saturation Density, Gravity (API) Viscosity Formation Volume factor

Compressibility

Reservoir Simulation Basics     

The reservoir is divided into a number of cells Basic data is provided for each cell Wells are positioned within the cells The required well production rates are specified as a function of time The equations are solved to give the pressure and saturations for each block as well as the production of each phase from each well

Reservoir Simulation (1) • Numerical model of reservoir made up of an array of cells. Equations are solved to calculate pressures and flows. • Fluid flow - underlying concepts • Conservation of mass • Darcy’s law • PVT model

1 2 3

4 5 6 7 8

9 10 11 12 13 14 15

16 17 18 19 20 21 22

23 24 27 25 26 26

•Partial differential equations are written in finite-difference form and solved numerically

Reservoir Simulation (2)



Input data:  Structural information, rock properties, fluid properties, well data, historical production and operating constraints



Results reported for each time step:  Grid block pressures and fluid saturations, fluid composition, well performance

 History matching:  The reservoir engineer tunes the input parameters to match past production performance

 Prediction:  Evaluate future performance for different operating strategies  Find and recover hydrocarbons left over from primary depletion  Use for reservoir management, economic decisions

WHAT BENEFITS ?

Golden Rule:

•You can only produce once •You can simulate many times

SIMULATION PROCESS -1 Simulation studies usually consist of the following phases: - Define objectives

- Data collection - Data review and analysis - Pre-simulation analysis - Select type of simulator - Model construction

SIMULATION PROCESS -2 - Fine grid modeling - Coarse grid modeling - History match - Predictions - Reporting

Overview of Modeling Procedure Describe reservoir

reservoir structure(seismic,logs) gross and net thickness(logs) well location and perforatd intervals

Design reservoir grid

porosity, permeability(logs, cores) fluid analyses(lab data) pressure and contacts(logs, well tests, etc.)

Select simulator model

black oil or compositional

fractured, condensate,etc horizontal wells, EOR, thermal, etc.

History match

Solve for pressures and saturations Predict and optmize future production

historical production data

investigate different scenarios visualize results

economic calculations

SCAL Rel. Permeability and Cap. Pressure Analysis

1

kro krw

RELATIVE PERMEABILITY

RELATIVE PERMEABILITY

1.2

Normalize

0.8 0.6 0.4

1.2

kro krw

1 0.8 0.6 0.4 0.2 0

0.2

0.6

0.65

0.7

0.75

0.8

0.85

WATER SATURATION 0 0

0.2

0.4

0.6

0.8

1

1.2

NORMALIZED WATER SATURATION

RELATIVE PERMEABILITY

EPS

Reseroir Simulation Grid

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

kro krw

WATER SATURATION

Rel. Permeability

Swc

1-Sor

WINPROP PVT-Analysis & Simulation

PVTi EOS PVT Analysis & Simulation FVF Creating a Fluid System Reseroir Simulation Grid

Simulating Experiments

Viscosity Export

Pressure Depletion Injection Study Single Point Separator

Match

Fitting an Equation of State

Schedule

   

Defines simulation wells, connections, vertical performance, artificial lift, controls and limits. Defines groups, controls and limits. Defines networks, compressors, etc. Specifies time dependent data.

Schematic of Data Handling in Schedule Simulation Grid Cell Properties

Wells - Path -Tubulars - Chokes - Completions - Workovers - Production - Injection

Geological Model

Network Groups

CTF

-Capacities GGS

-Demands OCS OCS

Problem Introduction •We have a small oil reservoir that began production on 1 January 1995. • Your initial job is to import an existing data set, edit the data, save the project, run and monitor simulation, view results vectors, and create reports.

Structure and Geology •The reservoir is 5000 meters by 5000 meters and 60 meters thick. • It has an anti-cline structure (see slides). • The structure and grid were created in the Eclipse GRID program,and input into the Eclipse data set in the GRID section.

Numerical Grid •The reservoir was sub-divided into a 10x10x4 grid. •The numerical layers correspond to the geological layers. •The x-y dimension of the grid blocks is 500 m by 500 m.

3-D Structure of Reservoir

Structure and Geology Layer Number

Porosity

Horiz. Perm (mD)

Thickness (m)

1

0.35

1000

5

2

0.3

5

10

3

0.25

300

15

4

0.2

100

30

Structure and Geology • Layer 2 has numerous shale components. • The geologists best guess of the average permeability of the mix of sand and shale is 5 Md. • The average Kv/K h ratio is 0.1. • The top of the structure is approximately 2989 m SSL. • The lowers edge of the reservoir in the aquifer is approximately 3090 m SSL.

Aquifer •There is a aquifer attached to the edge of the reservoir that provides an edge water drive. •The geologist has estimated that the aquifer has a volume of approximately 9 x 108 Sm3 of water and the aquifer productivity index is approximately 500 sm3/day/bar. • A analytical Fetkovich aquifer has be used to represent the aquifer.

PVT Data, Fluid Contacts, and Initial Fluids in Place •A PVT description has been generated with the Eclipse PVT program. • A live oil and dead gas system has been defined. •The bubble point pressure was determined as 331.65 barsa. •The Rs at the bubble point was 477.91 sm3/sm3 , and the Rs at a depth of 4000 m SSL was measured to be 486.60 sm3/sm3.

PVT Data, Fluid Contacts, and Initial Fluids in Place •The datum depth is the GOC = 3000 m SSL where the initial reservoir pressure is 331.65 barsa. •The water-oil contact was measured to be 3085 m SSL. •A small gas cap exists at the top of the structure.

PVT Data, Fluid Contacts, and Initial Fluids in Place •The reservoir has a •Pore Volume of 360.8 x106 Rm3 •Initial Oil In Place of 51 x106 Sm3 •Initial Water in Place of 173.6 x106 Sm3 •Initial Free Gas in Place of 77.56 x106 Sm3 •Initial Solution Gas in place of 24.4 x109 Sm3

x-y View of 4 Layers with Initial Water Saturations

x-z Cross-section with Initial Gas Saturations

Layer 1

Layer 2

Layer 3

Layer 4

x-z Cross-section with Initial Water Saturations July 03

7

July 03

July 03

9

8

Relative Permeability and Capillary Pressure • The relative permeability and capillary pressure were measured in the laboratory and are plotted in attached slides. • The connate water saturation is 0.22. • The critical/residual oil saturation in water is 0.35. • The critical oil saturation in gas with connate water is 0.2. • The critical gas saturation is 0.04.

Oil-Water Relative Permeability

Gas-Oil Relative Permeability

Pcow and Pcog July 03

July 03

15

July 03

16

17

Wells, Completions, Injection and Production Rates • Two production wells were drilled at locations 8,5 (called P85) and 3,5 (called P35) • Both completed in layers 2 and 3. •The producers operate, during the history, at a constant oil production rate of 1300 Sm3/day. • A water injection well and gas injection well were also drilled. •The water injection well was shut during the history.

Wells, Completions, Injection and Production Rates • The gas injection well called INJG was located in position 5,5 and completed in layer 1 in the gas cap. • The gas injector re-injects 1,000,000 Sm3/day of the produced gas. • This was designed to help maintain the reservoir pressure.