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StrataSimUser/Reference Guide

2004 Landmark Graphics Corporation

Part No. 162114 February 2004

StrataSimUser /Reference


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2004 Landmark Graphics Corporation

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Landmark StrataSim User / Reference Guide

R2003.12 Contents iii

StrataSim User / Reference Guide

Introduction

Overview............................................................................................................. 1

Main Advantages of StrataSim......................................................................... 2

Contents of This Guide..................................................................................... 3

Guide Conventions............................................................................................ 4

Preparing Data for StrataSim ........................................................................... 5

Starting StrataSim

Overview............................................................................................................. 6

Selecting the StrataSim Directory.................................................................... 6

Selecting a StrataSim Run................................................................................ 7

Creating a New Run ..................................................................................... 9

Re-Running a Previous Run........................................................................ 13

Modifying a Run Description ...................................................................... 13

Deleting a Run.............................................................................................. 14

Selecting Well Models....................................................................................... 15

Setting Units of Measurement.......................................................................... 16

Limiting the Size of the Simulation Model ...................................................... 17

Limiting the Model ....................................................................................... 18

Limiting the Size of the Upscaled Model ................................................... 20

Contents


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R2003.12 Contents iv

Workflow Manager

Overview............................................................................................................. 21

Reusing Existing Workflow Diagrams ....................................................... 21

Workflow Setup ................................................................................................. 22

Workflow Diagram............................................................................................. 23

Workflow Steps.................................................................................................. 24

Steps for Creating a Permeability Attribute............................................... 25

Steps for Creating an Initial Saturation Attribute...................................... 25

Steps for Investigating Flowbody and Volumetrics.................................. 25

Steps for Running a Unit Mobility Ratio Flow Simulation ........................ 26

Steps fpr Running a Unit Mobility Vertical Upscaling Simulation ........... 26

Estimating

Overview............................................................................................................. 28

Estimating Permeability.................................................................................... 29

Estimating Initial Oil Saturations ..................................................................... 33

Overview of Leverett J Functions............................................................... 33

Working with Leverett J Functions ............................................................ 34

Fitting a Leverett J Function.................................................................. 34

Cataloging Leverett J Functions........................................................... 37

Equilibrium Region(s).................................................................................. 40

Estimating Initial Saturations...................................................................... 41

Creating Hardcopy of Leverett J Functions .............................................. 43


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R2003.12 Contents v

Setting Up StrataSim

Overview............................................................................................................. 44

Describing Three-Dimensional Variables........................................................ 45

Setting Required Variables ......................................................................... 46

Calculating Transmissibilities .................................................................... 49

Permeability ............................................................................................ 49

Transmissibility Multipliers ................................................................... 50

Transmissibilities in StrataSim ............................................................. 51

Setting Transmissibilities ...................................................................... 52

Setting Optional Variables .......................................................................... 54

Constant Pressure Constraint............................................................... 55

Constant Flow Potential Constraint...................................................... 56

Reference Elevation ............................................................................... 56

Indicating Perforation ....................................................................................... 57

Setting Fluid and Rock Properties................................................................... 59

Using the Fluid and Rock Properties Dialog Box ..................................... 60

Setting Interfacial Tension................................................................................ 61

Well Boundary Conditions................................................................................ 62

Editing Well Conditions............................................................................... 64

Copying Well Conditions............................................................................. 66

Setting Run Parameters.................................................................................... 68

The Pressure Run ........................................................................................ 69
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R2003.12 Contents vi

Setting Run Parameters continued

The Saturation Run...................................................................................... 70

Porosity Cut-Off...................................................................................... 70

Permeability Cut-Off............................................................................... 70

Relative Movable Pore Volume Cut-Off ................................................ 71

Saturation Error ...................................................................................... 71

Water Cut Limit ....................................................................................... 71

Setting Output Options..................................................................................... 72

For a Regular Run........................................................................................ 72

Output at Starting Time ............................................................................... 73

Movable Oil Grid Files ................................................................................. 75

Time Steps.................................................................................................... 75

Adding Time Steps ................................................................................. 76

Deleting Time Steps ............................................................................... 77

Saturation Attributes ................................................................................... 78


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R2003.12 Contents vii

Running a Simulation

Overview............................................................................................................. 79

Specifying Output Attributes............................................................................ 80

Initializing the Pressure Solver ........................................................................ 82

Running a Simulation........................................................................................ 83

Reviewing Results............................................................................................. 86

During the Run ............................................................................................. 86

After the Run ................................................................................................ 87

Deleting Output Attributes................................................................................ 90

Exporting Run Results to ARIES ..................................................................... 91

Technical Reference

Overview............................................................................................................. 92

Darcys Law........................................................................................................ 94

An Example of Misinterpreting Darcys Law ............................................. 95

Hydrostatic Equilibrium............................................................................... 97

Two-Phase Flow ................................................................................................ 98

Darcys Law and Two-Phase Flow.............................................................. 98

Total Volumetric Flow Rate......................................................................... 99

Relative Permeabilities ................................................................................ 101

Unit Mobility Ratio........................................................................................ 103


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R2003.12 Contents viii

Transmissibility ................................................................................................. 105

Summary of Discussion .............................................................................. 106

Transmissibility in Z Direction.................................................................... 107

Transmissibility in X and Y Directions....................................................... 111

Transmissibility Multipliers......................................................................... 113

Comparisons of X, Y, and Z Transmissibilities ......................................... 114

Misinterpreting Darcys Law Revisited.................................................. 117

Using Transmissibilities in StrataSim........................................................ 119

Double Z Transmissibilities Near Very Thin Cells .................................... 120

Elimination of Zero Thickness Cells .......................................................... 121

When Cells Can Be Eliminated.............................................................. 121

How to Eliminate Zero Thickness Cells................................................ 122

Incompressible Flow Equations in StrataSim................................................. 125

Equation for Flow Potential......................................................................... 126

Flow Potential Equation for StrataSim....................................................... 130

Saturation Equation..................................................................................... 132

Upstream Weighting of Mobilities .............................................................. 135

Summary of Flow Equations....................................................................... 135


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R2003.12 Contents ix

Pressure-Constrained Cells ............................................................................. 136

Wells.............................................................................................................. 136

Well Types............................................................................................... 138

Reference Elevations ............................................................................. 139

Pressure Constraints ............................................................................. 139

Flow Rate Constraints............................................................................ 140

Phase Rates and Water Cuts for Wells................................................. 140

Perforations............................................................................................. 141

Pressure Constrained Nonwell Cells ......................................................... 142

Appendix A.

Running StrataSim in Standalone Mode

Running StrataSim ............................................................................................ 143

Appendix B. StrataSim Files

Overview............................................................................................................. 145

ASCII Files.......................................................................................................... 146

ASCII Control Files....................................................................................... 146

ASCII Output Files........................................................................................ 147

Miscellaneous ASCII Files ........................................................................... 148

Binary Output FilesZ ......................................................................................... 148


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R2003.12 Contents x

Index.................................................................................................................... 149


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R2003.12 Introduction 1

Introduction

Overview

StrataSim is a three-dimensional reservoir characterizationflow-analysis tool. Because of simplifications in the solutionalgorithms, StrataSim is able to run faster and require less memory thanfull-physics three-phase flow simulators. These qualities give you moreflexibility to investigate the effects of the geological detail inherent inmodels created by Stratamodel modeling programs. StrataSim can becharacterized as a steady-state single-phase simplified physicsflow-simulator.

StrataSim and standard reservoir flow simulators offer complementaryapproaches to understanding reservoir flow. Each approach offers yousomething that the other does not have.

Standard reservoir flow simulators use simplified geologicalmodels for investigating the effects of complex physics.

StrataSim uses simplified physics for investigating the effects ofcomplex geological models.

StrataSim helps you develop an understanding of how major features of

a reservoir model affect oil recovery. For example, you can investigatethe effects of permeability distribution, faults, or connectivity of sands.You can explore infill drilling of a mature reservoir or drilling deviatedwells on a new reservoir. You can use StrataSim to explore otherpossibilities as well.

Because of the simplified physics underpinning, it is easier to getresults. So geoscientists as well as reservoir engineers can use it to get abetter understanding of which features in the model affect the results,facilitating interdisciplinary communication.


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R2003.12 Introduction: Main Advantages of StrataSim 2

Main Advantages of StrataSim

StrataSim provides a quick sensitivity analysis for:

reservoir architecture

reservoir heterogeneity

effects of well placement on sweep efficiency

Other StrataSim features are:

speed of performing simulations

flow analysis within geological framework

easy visualization

no upscaling necessary

communication tool for geologists and reservoir engineers

complement to full-physics flow simulators

Difference Between High and Low Vertical Resolution Simulation

300 layer simulation (cross-section)

Typical StrataSim resolution

12 layer simulation (cross-section)

Typical Full-physics Simulatorresolution

ater n ecte rom e t to r g t


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R2003.12 Introduction: Contents of This Guide 3

Contents of This Guide

This guide contains the following sections:

Introduction provides an overview of the product and its

advantages, explains the books typographical conventions, andtells how to prepare data for use in StrataSim.

Starting StrataSimprovides instructions for starting the programand specifying project information.

Setting Up StrataSimprovides instructions for setting up yoursimulation run.

Running a Simulationtells how to run the simulation and viewthe results.

Technical Referenceprovides detailed information about how thesimulators calculates flow and transmissibilities and handles

pressure-constrained cells. Appendix A. Running StrataSim Standalonegives instructions

on how to start the program without running it from Stratamodel.

Appendix B. StrataSim Files explains the files that are importantto the program.


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R2003.12 Introduction: Guide Conventions 4

Guide Conventions

In StrataSim, certain conventions are used to explain how to access anduse various features of the program. A reference list is provided below:

Menu Options

key

Menu options and pushbutton names areprinted in boldface, for example, Setup.

Press the indicated key on the keyboard, forexample, Return.

enterstartow Text that you are required to enter is printed ina different typeface (Courier).Enter exactly what you see.

enterprojectname

A different typeface in italics (CourierItalics) indicates that you are to supply

information. At this instruction for example,you should enter the name of your project.

Click Move the cursor to the option or objectspecified and quickly press and release themouse button. Unless otherwise specified,use Button 1.

Press and drag Press the mouse button and continue to hold itdown while moving the cursor to the optionyou want or to a new location in the graphicdisplay area; then release the button.

Highlight In a dialog box, move the cursor to the name of the item you wish to use and select it with themouse.

Select Move the cursor to the option or object youwant to select and click it.

Double-click Click the mouse button twice rapidly withoutmoving the mouse. The first click highlightsthe option, object, or text beneath the cursor;the second click is equivalent to pressing the

OKbutton to accept the selection.

Triple-click Click the mouse button three times rapidlywithout moving the mouse to highlight a stringof text (more than one word) beneath thecursor.


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R2003.12 Introduction: Preparing Data for StrataSim 5

Preparing Data for StrataSim

StrataSim can be run after you have created an Attribute Model inStratamodel that contains porosity and permeability.

You have the following flexibility in StrataSim.

You can have the program read initial saturations (for example,irreducible water saturation) from the Attribute Model, or you canspecify them as constants in StrataSim.

You can assign saturations to every cell in the model usinginterpolation techniques, you can model operations in Stratamodel,or you can use StrataSims estimation capability.

You can supply pressure or flow potential information using wellsor attribute fields.

You can specify well conditions as pressure- or flow-constrainedand non-well cell boundary conditions as pressures or flowpotentials. You can incorporate aquifer pressure information intothe simulation run using model operations in Stratamodel.

Perforation information and well locations are supplied by WellModels. Building Well Models is a standard procedure in creating aStratamodel Attribute Model. You can change well configurations byrebuilding a Well Model.

Simplified Physics Assumptions

Invading Fluid Properties = Displaced Fluid Properties. Incompressible Flow (Steady-State).

The volume of the fluids in the reservoir does not change with pressure.

Mobility Ratio equals one.

There are no Capillary Pressure Effects.

Steady-State

The rate of change of pressure with time is zero, which is most applicable in the

case of secondary recovery (e.g., waterflood, pressure maintenance scheme).


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R2003.12 Starting StrataSim 6

Starting StrataSim

Overview

This section explains how to perform the followingtasks, whichprepare your StrataSim run for work:

selecting a StrataSim directory

selecting a StrataSim run

selecting well models

setting units of measurement

Selecting the StrataSim Directory

If you are starting StrataSim as a continuation of a Stratamodel task,you will have already selected your project information

Start StrataSim by using one of the two following methods:

Select Commands SIM StrataSim Fluid-Flow Analysis fromthe Stratamodel menu.

Single-click a StrataSim icon in the icon menu.

Selecting either of these options opens the Specify Run Descriptiondialog box and the StrataSim main window with all its options inactive.


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R2003.12 Starting StrataSim: Selecting a StrataSim Run 7

Selecting a StrataSim Run

The first dialog box that appears for StrataSim lists the different runs. Ifyou have not run any simulations, the list of StrataSim Descriptions isempty. A run contains all the input needed to run a simulation.

The program uses runs to save input and output. Whenever you create anew run, you use an old run or the defaults as a template for yourproject, then change the settings you want to be different.


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Once you have selected a run description, you will be asked to select aWell Model. You can select none, one, or many. After the Well Modelselection, the StrataSim main window options become active:


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Creating a New Run

A likely course you may want to follow when you first enter theprogram is to create a new run of your project.

1. You have three options for beginning a run:

If you have not run StrataSim previously, there are no runs inthe list at the top of the window and the Createbutton is theonly one active. In that case, clickCreate, then go on to step 2onpage 11.


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If you have a list of previous runs, but you want to create anentirely new run based on program defaults, clickCreatewithany run selected. Then go on to step 2onpage 11.

Defaults Alone Do Not Provide a Solution

The defaults alone, with no changes, will not provide a solution if runimmediately, because all the wells are plugged in the default values.At a minimum, you must provide a source of flow, either by changingConstant Pressure Cells or Constant Potential Cells underThree-Dimensional Variables or by unplugging some of the wellsunder Well Conditions.

Click Create.

Select any

run.


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If you want to base your new run on a previous run, click theprevious run, then clickCopy.

2. Click OK.

The StrataSim Run Description dialog box appears. This dialogbox indicates either that you are using the default data or copyingfrom a previous run.

3. Select the input files you want to copy and enter the name in theEnter New StrataSim Run Description field. You do not have to

enter a number, StrataSim automatically numbers the run for you.It is a good idea to give the run a description that identifies whatattributes you intend to work with so that you can identify the runlater.

4. Enter a name into the Enter New StrataSim Run Description field.You do not have to enter a number, as StrataSim will number it foryou. It is a good idea to give the run a description that identifieswhat attributes you intend to work with so that you can identifythat run later. ClickOKto close the box. Your new run nowappears in the list of runs.

Click Copy.

Select a

previous run.


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If you designated certain files to be copied the following dialogappears to show you which fields were copied. To close thisinformation dialog, clickOK.


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Re-Running a Previous Run

To rerun a previous run with no changes to the description

1. Select the run.

2. Click OK.

You can now set up your run. See Estimating on page 28.

Modifying a Run Description

Suppose you decided that a run name is not descriptive enough.

1. Select the run name.

2. Click Modify.

3. Enter a new description in the StrataSim Run Description dialogbox:

4. Click OK. The run description now appears changed in the list.

Select a

previous run.

Click OK.


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Deleting a Run

You may want to delete a run. When you do, the run disappears fromthe list and the other runs are renumbered. Delete removes all of thefollowing:

output files input files

StrataSim-generated attributes

To delete a run

1. Select the run you want to delete.

2. Click Delete. You are asked to verify whether you want to deletethe files.

3. Select Yes if you still want to delete the files. StrataSim completelydeletes the run and renumbers the remaining runs.


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R2003.12 Starting StrataSim: Selecting Well Models 15

Selecting Well Models

In Stratamodel you may have created several well models because yourwell files were formatted differently or to differentiate groups of wellsin your display. Your first activity when running StrataSim is to specifywhich of the well models you want to use in the simulation. If you donot wish to select a well model, you must specify a constant pressure orconstant flow potential in the three-dimensional variables before youcan run a simulation; otherwise, you have not specified a driving forcefor flow.

1. Usually this dialog box comes up automatically when you havemore than one well model. But if you wish to change your choice,select Session Select Well Models.

2. Choose the well model or models to use in the simulation.Select or release well models by clicking them.

3. Click OKwhen you finish selecting models.


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R2003.12 Starting StrataSim: Setting Units of Measurement 16

Setting Units of Measurement

Although it is not required, it is a good idea to set the units ofmeasurement before you make other specifications.

1. Select Session Units of Measurement.

2. Set each unit by clicking the menu and selecting it.

3. Once you set the units, clickOK. All menus that use these unitsare updated.

Stratamodel Units Must Match

All units in this dialog box labeled with SGM (SGM Elevation, SGMDistance, and so on) must match the units used to construct yourStratigraphic Framework Model and your Stratamodel Attribute Model.


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R2003.12 Starting StrataSim: Limiting the Size of the Simulation Model 17

Limiting the Size of the Simulation Model

StrataSim provides two ways to limit the size of the model:

Simulating the whole of a very large model may take time and

computing power. Sometimes, simulating only a subset of thatmodel can give you the results you need. Session Limit Size ofModel SGM allows you to isolate a portion of the StratigraphicFramework for simulation by limiting the size of the model to aspecific number of sequences, zones, or blocks.

Running StrataSim simulates fluid flow at the resolution of theStratamodel model. You may want to upscale your model to aresolution that is more common with larger-scale simulationengines. Session Limit Size of Model Upscaleallows youto express the model as a fraction of the number of Stratamodel

cells.


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Limiting the Model

To simply reduce the size of the model, follow these instructions.

1. Select Session Limit Size of Model SGM.


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2. Use the slider bars to limit the columns and rows. As you move thesliders, the information below about the size of the StrataSimModel changes.

3. You can choose to Include the highlighted sequences, zones orblocks or to Exclude the highlighted ones by pressing theappropriate radio button.

4. Depending on your choice in step 3, highlight either thesequences, zones, and blocks to include or exclude:

5. When you have limited your model, clickOKagain.

If you movethesliderbar..

the information

changes.


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Limiting the Size of the Upscaled Model

You can choose StrataSims upscaling capability by specifying the sizeof the upscaled model. Upscale allows you to target the number ofupscaled cells, expressed as a fraction of the total number of cells in themodel. The actual number of cells may vary from the target number

because of the following constraints:

There must be at least one upscaled cell per stack.

Cells with a high fluid flow rate may not be lumped together.

Upscaled cells must be from the same StrataSim flowbody.

Upscaled cells may not be greater in volume than the maximumvolume constraint you select.

To upscale the model, follow these instructions:

1. Select Session Limit Size of Model Upscale.

2. Use the top slider to target a number of upscaled cells as a fractionof the total number of cells in the model.

3. Use the middle slider to select a minimum cell volume, expressedas a fraction of the average cell volume. This constraint assuresthat small cells will be lumped.

4. Use the bottom slider to select the maximum cell volume, also

expressed as a multiple of the average cell volume. This constraintassures that there will be more than one upscaled cell per stack.

5. Click OKto upscale the model.


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R2003.12 Workflow Manager 21

Workflow Manager

Overview

The Workflow Manager is designed to simplify tasks within the mostcommon StrataSim workflows. The manager leads you step-by-stepthrough the process of creating attributes or running several differenttypes of simulations with an easy to follow workflow chart. Two menuoptions (Session Workflow SetuporManager) control theWorkflow Manager dialog boxes.

In the Setupdialog, you choose which procedures you want to

accomplish. A Workflow Chartis generated based on your selectionsin the Setupdialog. This chart contains buttons to represent each stepneeded to accomplish the tasks. As you select each step or button in thechart, StrataSim opens the appropriate dialog for you to complete.

As of release 2003, when you enter StrataSim, a dialog offers you theopportunity to use the Workflow Manager immediately:

If you clickYes, the Workflow-Setupdialog box appears.

Reusing Existing Workflow Diagrams

If a workflow diagram exists for the current StrataSim run, a dialogappears to allow you to choose from the following options:

1. Go to the current workflow manager.2. Cancel out of the window.

3. Reset the workflow.

4. Remove the current workflow.


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R2003.12 Workflow Manager: Workflow Setup 22

Workflow Setup

When you select the Session Workflow Setupmenu command,the Workflow-Setupdialog appears. This dialog allows you to choosewhich pre-defined task(s) or workflow(s) to construct.

To select any of these procedures for your workflow chart, click in thebox preceding the title. You can select multiple workflows. In theproceeding illustration, all the workflows have been selected.


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R2003.12 Workflow Manager: Workflow Diagram 23

Workflow Diagram

If you select Session Workflow Manager, the Dialog FlowChartappears to lead you through the tasks you selected with theSetupcommand. The example pictured below chose to run all thedifferent kinds of simulations offered in the Setup dialog box.


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R2003.12 Workflow Manager: Workflow Steps 24

Workflow Steps

Each button represents a step in the workflow and is color coded to helpyou track your progress:

Each button opens a StrataSim dialog. Fill out the values in each dialogand clickOK. If you need help on any dialog, press the Helpbutton on

the dialog and developers notes appear.

When you close a dialog, the Workflow button turns to green to indicatethat step has been completed successfully.

Button Color Meaning

Red This step is suggested and has not been visited. If you skip a red button, a warning message appears asking you to verify yourdecision.

Yellow This step is optional. You do not need to accomplish this task tocomplete the workflow.

Green A step that has successfully been completed.

Completed steps are green. Optional steps are yellow.

Red steps are not yet completed.


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Steps for Creating a Permeability Attribute

There are three steps in this workflow:

1. Units of Measurement (page 16)

2. Limit StrataSim Model Size (page 17)

3. Permeability Attribute (page 29)

Steps for Creating an Initial Saturation Attribute

There are up to 8 possible steps in this workflow:



3. Select Well Model(s) (page 15)

4. Interfacial Tension (page 61)

5. Leverett J Curves Fit - Cores (page 34)

6. Leverett J Catalog - an optional step performed to review the list ofJ Functions

7. Equilibrium Region(s) (PVT Regions)

8. Initial Saturations (page 78)

Steps for Investigating Flowbody and VolumetricsThere are up to 10 possible steps in this workflow:



3. SGM: Create Well Model(s) - an optional step performed in theCreate Wells feature in Stratamodel. (page 62)


5. Well Conditions - Perforations (page 64)

orWell Conditions - Specify (page 64)

6. Run Parameters (page 45)

7. Output Options StrataSim (page 72)

8. StrataSim Physics (Simple)

9. Flowbody Analysis


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Steps for Running a Unit Mobility Ratio Flow Simulation





4. Fluid and Rock Properties (page 59)

5. 3D Variables (page 46)

6. Well Conditions - Perforations (page 64)orWell Conditions - Specify (page 64)

7. Run Parameters (page 45)

8. Output Options StrataSim (page 72)


10. Flowbody AnalysisorProduction Plots

11. Contacted Oil Nearest Well

12. Tabulated Results

Steps fpr Running a Unit Mobility Vertical Upscaling Simulation




3. Limit Upscaled Model Size


5. Fluid and Rock Properties (page 59)

6. 3D Variables (page 46)

7. Well Conditions - Perforations (page 64)orWell Conditions - Specify (page 64)

8. Run Parameters


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9. Output Options StrataSim (page 72)orOutput Options Upscale


11. Flowbody Analysis12. Tabulated Results

Description Panel

This area displays information telling you why this step is needed asyou roll your cursor over the workflow buttons.


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R2003.12 Estimating 28

Estimating

Overview

The Estimation modules help you build attributes for two importantvariables that are not well suited for simple interpolation from well datainto a 3D geological model: permeability and initial oil saturation.

StrataSim estimates permeability from porosity as a function of apermeability indicator. It also estimates initial oil saturation fromLeverett J functions, which depend upon indicators.

Calculating initial oil saturations involves the following steps:1. Specify capillary pressure data.

2. Fit one or more Leverett J Functions to the capillary pressure data.

3. Estimate initial oil saturation from the Leverett J Functions as afunction a free water elevation. The J function can depend on anindicator that can be a continuous variable (such as V Shale) or adiscrete variable (such as lithofacies). The free water elevation candepend on sequence number.

These methods provide an alternative for estimates that rely solely on

interpolations from well logs. In the process, StrataSim identifiespossible sources of error in capillary pressure measurements.

StrataSim uses Leverett J Functions as the basis of this approach forestimating oil saturations. For more information, see Overview ofLeverett J Functions on page 33.


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R2003.12 Estimating: Estimating Permeability 29

Estimating Permeability

You can use known porosity values to estimate permeability based on apermeability indicator (a function and two points on a permeability/porosity crossplot). If you do not specify a permeability indicator, thesame permeability/porosity correlation is used for the entire model.

1. Select Estimation Permeability. The Estimate Permeabilityfrom Porosity dialog box appears:

2. Click the Attributebutton next to Porosityto select the porosityattribute. Select an attribute from the resulting list and clickOK.

3. Choose whether the Permeability Indicatoris a function of aDiscrete(lithofacies, sequence number, reservoir zone) orContinuous(V shale, clay content, gamma ray log reading)variable.

If the correlation depends upon a discrete indicator and ifStrataSim encounters an indicator cell value that does notappear in the table, it sets the permeability of that cell using the

default (Indicator = 0) correlation. If a default is not provided itsets the cell value to null.

If the correlation depends on a continuous indicator, StrataSimlinearly interpolates between two indicator values in the tableat the bottom of the dialog box. If the indicator value does notfall between the two values, then the permeability of that cell isset to null.


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4. Click the Permeability Indicator Attributebutton to select thepermeability attribute, if desired. If you choose None Selected thenthe same Permeability-Porosity correlation is used for the entiremodel. Select an attribute from the resulting list and clickOK.

5. At the bottom of the dialog box, use the button to add, modify, or

delete a permeability/porosity correlation.

Any values outside the correlations described in this table are setto null, as explained in step 3. Choose wheter the PermeabilityIndicator is a function of a Discrete (lithofacies, sequence number,reservoir zone) orContinuous(Vshale, clay content, gamma raylog reading) variable. The correlations used for this calculation aretwo-parameter fits, so it is necessary only to add two points foreach entry in the table.

If you add or modify a correlation, the following dialog box

appears:

6. Enter a value for the Permeability Indicator. This value can be

either an integer (for a discrete attribute) or float (for a continuousattribute), depending upon your choice in step 3. Choose whetherthe Permeability Indicator is a function of a Discrete orContinuous vaiable. The indicator is zero for the defaultcorrelation, which is used whenever other values in the table donot apply.


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7. Select a Type of Correlation.In the equations explained in thebullets below, porosity is expressed in fractions (specified in Unitsof Measurement). StrataSim adjusts if your choice for units ispercent.

Semi Log crossplots of permeability and porosity are most

commonly represented by the log of the permeability on theordinate, oryaxis.

Log-Log1 this is a generalized form of the Kozeny equation(explained in the next bullet), suggested by Timur in 1968.

Log-Log2 Kozenys equation is to plot log(k/(1-por) againstlog(por/(1-por). When porosity is very small, the denominatorsof the arguments are close to 1, thus collapsing to Timursgeneralized equation (Log-Log1).

8. Enter a porosity cut-off, if desired. For porosities below this cut-

off, the permeability is set to zero.

9. Enter two points for a correlation between porosity andpermeability.

10. Select a sequence to Include or Exclude. All sequences areincluded in the preceding illustration.

11. ClickOK.

12. Continue to add as many correlations as needed, repeating step 5through 11. At the bottom of the dialog box, use the button to add

modify or delete a permeability/porosity correlation. Any valuesoutside the correlations described in this table are set to null asdescribed in Step 4. Choose whether the Permeability Indicator isa Discrete or Continuous variable. The correlations used for thiscalculator are two-parameter fits, so it is only necessary to add twopoints for each entry in the table. It is a good idea to specify adefault correlation, signified by Indicator = 0.

For a discrete indicator, you must specify a correlation for allvalues contained in the Stratamodel Attribute Model, cells forwhich no value has been specified will be set to null.

For a continuous indicator, you must specify a range ofcorrelation that includes all values in the Stratamodel AttributeModel, or the default is used; in case of no default, the cell isset to null.


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13. When the correlation table at the bottom of the dialog box reflectsthe correct values for your attributes, clickCalculateto calculateestimated permeability and save the selections in the dialog box orclickSaveto save the selections without calculating.

If you clickCalculate, an xterm reports the progress of the

calculation and informs you of the name of the created attributethat contains the permeability. You can view the permeability inShow Displays.

14. Press Enterto close the xterm.


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R2003.12 Estimating: Estimating Initial Oil Saturations 33

Estimating Initial Oil Saturations

StrataSim uses laboratory measurements of capillary pressure todetermine initial oil saturation, through the following steps:

Specify the capillary pressure data curves to fit with the Leverett JFunction.

Fit one or more Leverett J Functions to the capillary pressure data.

Estimate initial oil saturation from the Leverett J Functions as afunction a free water elevation. The J function can depend on anindicator that can be either continuous or discrete. The freewaterelevation can depend on sequence number.

This section explains the procedures for completing this estimation.

Overview of Leverett J Functions

The remaining items on the Estimation menu use the Leverett JFunction as a basis for calculating Initial Oil Saturation. The function isdefined as:

wherekdenotes permeability andpordenotes porosity.

This function is dimensionless. To see that this is so, note that in the cgssystem of units, capillary pressure is in dyne/cm2 and permeability is incm2. So, the Leverett J Function can be thought of as a dimensionlesscapillary pressure.

The Leverett J function is important because in general, two coresamples that have different permeabilities or porosities have differentcapillary pressure curves. Consequently, complex models that containmore than a million cells could require millions of measurements todescribe the necessary capillary pressure curves.

Leverett identified a way around this problem by noticing that it was

easier to correlation capillary pressure curves when he plotted the JFunction on theyaxis. The advantage of his approach is that capillarypressure curves from various core samples with different permeabilitiesand porosities can be plotted using a single J function curve.

Leverett J functions are typically correlated with parameters such aslithology, shale volume, or porosity.

J(Capillary Pressure)

InterfacialTension( ) (Contact Angle)--------------------------------------------------------------------------------------------------- k por ( )=


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Working with Leverett J Functions

The choices under the Estimation Leverett J Functionmenuenable you to fit a Leverett J Function to selected capillary pressurecurves or to maintain a catalog of Leverett J functions. For moreinformation about these functions, see the previous overview of

Leveritt J functions.

The catalog lists the template files included with StrataSim along withall of your fitted J functions.

Fitting a Leverett J Function

You must have at least one capillary pressure file set to fit a function.

StrataSim helps diagnose two types of errors when attempting to fit afunction.

A negative Irreducible Saturation can indicate an underestimatedpore volume. You can test for this by selecting VariableforIrreducible Saturation. See Step 4.

In the entry region of the curve, the Wetting Phase Saturation isexpected to remain 1 (or 100, in percent) until a displacementpressure is overcome. Sometimes a curve exceeds thedisplacement pressure at a lower saturation, say 0.95. This usuallyindicates the presence of a dead volume in the experimentalapparatus. Instead of filling the core sample, the nonwetting phasewas filling up void space in the apparatus.

To fit a Leverett J Function, follow these steps:

1. Select Estimation Leverett J Function.


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2. Select one or more capillary pressure curve files from the list. Youcan see the curve in the graphic at the bottom right of the window.

Use the buttons above the graphic to examine the curve.If no capillary pressure curves exist, you can import a curve froman ASCII file by clicking the Import Curvebutton.

3. Choose a fitting from the Fitting Function buttons:

Most curves can be fit using either the OMeara Unimodal orThomeer model

Brooks-Corey and Benson-Anli fit for special cases but do notseem to have widespread applicability.

Select the OMeara Bimodal for curves that exhibit bimodal

behaviour and for more flexibility for hard-to-fit unimodalcurves.


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4. Choose a method to handling values below zero from theIrreducible Saturation field:

Select Variable(the default) to explore whether there are

errors in the measured data. If a fit encounters a negativeIrreducible Wetting Phase Saturation, an error message appearsto indicate that there may be underestimation in the porevolume of the core sample. Once you have verified that thereare no errors, refit the curve using Negative Not Allowed.

Select Negative Not Allowedif you are confident of no errorsin the measured data, since values of saturation below zero arenot physical.

.

5. Fit the curve by clicking the Fit Curvebutton under the list ofcurves. It will take probably take a few minutes to return a fit or abit longer for the bimodal curve, which fits eight parameters. If theprogram has problems fitting the curve, an informative errormessage suggests some solutions.

Goodness of Fit is shown once the fit is finished. The lower thevalue, the better. This criterion is equal to the sum of the squares ofthe residuals of the fit.

6. Click OKwhen you have a good fit.

7. A dialog box appears allowing you to enter a filename for the fittedfunction. This function is saved in your project directory file withan extension of.jff_ss.

Results of Using Negative Irreducible Saturation

If a curve with a negative irreducible saturation is used in theEstimation: Initial Oil Saturation dialog box, StrataSim limits thelowest calculated oil saturation to zero so that saturations that are not

physical do not appear in your Stratamodel Attribute Model.


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8. Enter a description of the function. The description can be up to 80characters long.

9. Click OKto save the J Function.

Cataloging Leverett J Functions

StrataSim provides a catalog for keeping track of your Leverett JFunctions. The catalog includes templates that have been provided withthe program. You can use the catalog to locate a template or previouslyfit function that most closely matches your needs. Template functionscannot be modified, so you must copy them first to your projectdirectory.

To create your own template of previously fitted Leverett J Functions,simply copy (with superuser permission) a J function file (with theextension .jfn) from your project directory to the StrataSim Templatedirectory called StrataSim.tpl, which resides in your installationdirectory.

To view the catalog

1. Select Estimation Leverett J Function Catalog.

2. Click a template or fitted curve.


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Comparing Functions

You can compare functions by selecting more than one from the list andclicking the Comparebutton. A dialog box like the following appears:

You can use the buttons at the top of the dialog box to manipulate thecurves for a better view, or you can change the Y Axis Maximum anduse the Re-Plotbutton.

Copying Functions

You can copy a function for future modifying. You must copy templatefiles before you can modify them.

1. Click the Copybutton.

2. Enter a file name and a description in the dialog box that appears.

3. Click OK. The copied file is now available for use in your project.


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Viewing or Modifying a Function

You can view any function, but you cannot modify template functions.If the data that went into fitting a J function is available in yourStratamodel project directory, this dialog box allows you to view italong with the fit.

1. Click View/Modify. The dialog box shows a view of the functionon the bottom right. If you are viewing the function, you can usethe buttons above the graphic to change the view. When you arefinished viewing, skip to step 6. If you are modifying the function,continue on to the next step.

2. For copied or modified files only, enter a new name in the filenamebox. The file will be copied into the project directory with theextension .jfn_ss.

3. Enter a description of the file.

4. Change the values for the Irreducible Wetting Phase Saturationand Leverett J Function Displacement Value if desired.

5. The parameters that are unique to a particular function appear inthe boxed field. To change a value, select the parameter and enter anew value into the field.

6. When you finish modifying the function, clickOKto save themodifications.

Removing Functions

You can remove functions by using ClearorDelete.

Use Clear to remove all functions from the list.

Use Deleteto select and delete functions that are not templates.


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Equilibrium Region(s)

The next step is to create one or more equilibrium regions.

1. Select Estimation Equilibrium Region(s).

2. Optional: To add a new region, click the Addbutton..

3. Select a Free Water Elevation and the associated sequence(s),zone(s), or block(s).

4. Click OKto add the region. The new region appears in the list ofequilibrium regions.


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5. Repeat the previous step for each region you want to include.

6. Click OKto accept and save all changes.

Estimating Initial Saturations

Once you have fit one or more Leverett J Functions, you can estimateinitial saturations from them.

1. Select Estimation Initial Saturation.

2. Select an attribute forPorosityby clicking the Attributebuttonand choosing one from the list. ClickOK.

3. Select an attribute forIndicatorby clicking the Attributebutton

and choose one from the list. ClickOK.

4. Select an attribute forPermeabilityby clicking the Attributebutton and choosing one from the list. ClickOK.

5. Optional: To create a grid of the fluid contact, click the check boxforOutput Fluid Contact Grid File. A grid is provided for freewater elevation.


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6. Optional: To control the output, use these features:

Null orAll Water for the Undefined Leverett J Function underOutput Options.

Attributes for the Equilibrium Regions and Aquifer Potential

by clicking Yes.

Fluid Contact Grid File(s) by clicking Yes.

To grade the undefined placement as Optimistic, Neutral, orPessimistic.

7. In the table, add the J Leverett functions the system will use tocompute the Initial Saturation. Click theAddbutton.

8. Enter the J Function Indicator.

If you have only one J function in the table, use the default of0. If

you enter another value, an error message appears.

9. Select the file from the list. You can use the graphic and button atthe bottom of the dialog box to examine the functions.

10. ClickOK.

11. When you have the functions you want, click the Calculatebuttonto compute the Initial Saturation. An xterm appears that reports theprogress of the calculation and tells you the name and number ofthe newly calculated initial saturation attribute in your model.Press Enterto close the xterm.

You can view your output or the attribute for initial saturation or the oil/water contact grid in Stratamodel by using Show Displays.


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Creating Hardcopy of Leverett J Functions

From the catalog dialog box, the curve-fitting dialog box, or the tabledialog box under Estimate Initial Oil Saturation, you can print ahardcopy of the functions.

1. Click Hardcopy.

2. Provide a name for the hardcopy file, which will be written as apostscript file with an extension of .ps.

3. Click OK.

4. Print the file by using standard Unix commands.


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R2003.12 Setting Up StrataSim 44

Setting Up StrataSim

Overview

To set up StrataSim, complete the following tasks:

Describe three-dimensional input variables from the AttributeModel.

Specify perforated intervals from the Well Model.

Adjust fluid and rock properties to obtain a mobility ratio of one.

Specify well conditions.

Set up parameters for the pressure and saturation solutions.

Specify the content and timing of the output.

The first option on the Sessionmenu, Run Description, isautomatically set if you have been running from StrataModel.(For information about the geological model, see Selecting theStrataSim Directory on page 6. For information about runs, seeSelecting a StrataSim Run on page 7.) This option is included in theSessionmenu so you can reset it at any time, as long as you are not

running StrataSim in standalone mode (without running StrataModel).If you are running standalone, this option reminds you what you chosewhen you set up the model and project.


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R2003.12 Setting Up StrataSim: Describing Three-Dimensional Variables 45

Describing Three-Dimensional Variables

Next you have the option to describe the three-dimensional variablesthe simulation uses as input. StrataSim provides defaults for allvariables. However, it is a good idea to check and consider modifyingthe following values:

Porosity

Initial Saturation

Residual Oil

Immobile Water

Permeabilities

The other variables are optional.

Units for the constant values for these settings are determined in the

Units of Measurement dialog box.

Volumetrics

Optional

Variables

Transmissibilities


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For most runs, you describe Porosity, Initial Saturation, andpermeability in the Attribute Model. For simpler runs, you can set theremaining variables to constants, which saves space in the AttributeModel.

Setting Required Variables

1. Select Setup Three-Dimensional Variables.

2. From the Porositymenu,choose whether to specify a constant

porosity or a variable porosity described by an attribute field.

If you chose Attribute Field, a list of the appropriate attributesfor this field appears. StrataSim makes it easy to find theattributes by giving you a list of the attributes that excludesStrataSim-generated attributes. Click an attribute field, thenclickOK.

If you chose Constant,enter a constant value, expressed in theunits you chose under Units of Measurement, into the text fieldbeside the attribute constant, and clickOK.

Looking at the Attribute Model

You may want to pull up a display of your Attribute Model from Show Displaysin Stratamodel while you are providing information for setting these variables.


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3. For Initial Saturation, choose oilorwater.

4. Click the menu button and choose whether to specify a constantvalue for saturation or a variable attribute. Make specifications inthe dialog boxes that appear, as you did for Porosity.

StrataSim calculates the initial saturations of the second phase. Forexample, if you choose the initial oil saturation to be 0.3 (30%),

the calculated initial water saturation for all of the cells in yourmodel will be 0.7 (70%).

If you specify the initial oil saturations to be read from an attributefield, StrataSim calculates the corresponding water saturation foreach individual cell in the model. The units for saturations readfrom the Attribute Model can be either a fraction or percent andcan be specified later in the session.

Appropriate Choices for Saturation Attributes

When StrataSim offers appropriate choices for saturation attributes, itcannot exclude StrataSim output. Suppose, for example, youwant to start upa new run when the last one ended. In this case, the final saturation for thefirst run becomes the initial saturation for the second run. Because of such

possibilities, saturation output from previous runs must be included forconsideration.

Phase 2 = 1.0 - Phase 1


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Saturation Considerations in StrataSim & Stratamodel

Oil saturation values interpolated along the layers of the

Stratigraphic Framework

Oil saturation values assigned to cells using depth information

Saturations vary with depth

Saturations adjusted to depth

Since saturation distributions can

cross-cut stratigraphy, it is often

necessary to distribute saturation

data using depth information.This

canbe performedusing tools from

Stratamodel or by StrataSims

Estimationmodule, usingLeverettJ functions.


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5. Follow the same instructions forResidual OilandImmobile Water.

Calculating Transmissibilities

A transmissibility value is associated with the interfacial area betweentwo cells. Transmissibilities are a function of permeability, cellgeometry, and transmissibility multipliers associated with the interfacebetween cells.

Permeability

Different permeabilities for thex, y,andzdirections are available. Forexample, thex andypermeability may have been averaged in the wellmodel using a thickness-weighted arithmetic average, while thezpermeability was averaged using a harmonic average in the wellmodel. The result will be that the values for the interpolatedpermeabilities in thexandydirection are higher than thezpermeabilities.

You can modify permeabilities after interpolation using modeloperations in Stratamodel.

100% saturation = im-mobile water + residual oil saturation + initialmovable oil saturation + initial movable water saturation

X Location of XTransmissibility


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Transmissibility Multipliers

You may wish to apply a multiplier to transmissibilities that arecalculated using only permeabilities and a cross-sectional area betweenadjoining cells. Multipliers, for example, can be useful for modelingshales that are too thin to include explicitly in your Stratigraphic

Framework. You can create three-dimensional multiplier fields for thex,y, andztransmissibility using Stratamodel templates or ModelOperations.

You can also use a transmissibility multiplier and a barrier attribute thatsignals a change across a cell face to investigate, for example, the effectof barriers to flow because of changes in sequence, layer, or lithology.

For example, suppose you wanted to investigate what happens whenthere is no flow across sequence boundaries. You would selectSequence Number for the barrier attribute and set the TransmissibilitiesMultiplier to zero.

Fault Zone Properties

If you have used Badleys Fault Seal Analysis in Stratamodel, you may importfault zone thickness and permeability attributes. StrataSim uses cell connectioninformation to apply these attributes across cell interfaces that occur in fault zones.


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Transmissibilities in StrataSim

The general definition of transmissibility in the x-direction is:

Injector Producer

Injector Producer

Injector Producer

Injected fluids are allowed to

cross the sequence and layer

boundaries

Injected fluids are not

allowed to cross the

sequence boundaries

Injected fluids are not

allowed to cross the layer

boundaries

Injector

Injector

Injector

Attribute = 0

Multiplier = 0.0

Attribute =

Sequences

Multiplier = 0.0

Attribute =

Layers

Multiplier = 0.0

Flow with transmissibility

dependence using layers

Flow with transmissibility

dependence using sequences

Flow without transmissibility

dependence

Txi TMxi2yx

----------z1 1z2 2

z1k1 z2k2+-------------------------------------=


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You can comparex, y,andztransmissibilities if you assume that twoneighboring cells have the same cell thickness. Assuming that thex, y,

andzpermeabilities are isotropic (the same in all directions), thetransmissibilities are then defined as follows:

The z transmissibilities are much higher than x and y transmissibilitiesbecausezis typically much smaller thanxandy.

Setting Transmissibilities

To set transmissibilities, follow these steps:

1. The permeability variables are required for all simulations.

Click the button next to X Permeability, and choose eitherAttribute FieldorConstant.

If you choose Attribute Field, select an attribute you built forpermeability in the Attribute Model from the resulting dialogbox and clickOK.

If you choose Constant, enter a constant in the dialog box thatappears and clickOK.

Assume:x =y = 100 ft.z= 1 ft.

Assume that k1= 10 md and k2= 1 md

Then:

Tx= 6.67

Ty= 6.67

Tz= 66,666.67

Ratio Tz/Tx= 9995.0

X Location ofX Transmissibility

Z1 Z2

k1 k2 Variable Name

TMxi transmissibility multiplied in

direction

z, z2 cell lengthsk1 xpermeability for cell 1

x, y cell width and thickness

Location of

X Permeabilities

at cell centers

Tx2yz

x-----------------

k1k2k1 k2+------------------=

Ty2xz

y-----------------

k1k2k1 k2+------------------=

Tz2xy

z----------------- k1k2

k1 k2+------------------=


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2. Repeat step 1 forY Permeability andZ Permeability. Remembertat these variables are required.

3. Optional: To apply a multiplier, use the same procedure again tospecify a constant multiplier or to read one from the attributemodel forx, y,andz.If you do not pick a value for the multiplier,

the default value of1assures that there is no implication.Transmissibility is calculated from permeability and the cellgeometry.

4. Optional: To investigate the effect of barriers to flow because ofchanges in sequence, layer, lithology, and so on, use the followingtwo barrier selections, which interact with each other.

You can choose an attribute (Attribute for Barriers(a)) whosechange across a cell face will signal the application of atransmissibility multiplier(Barrier Trans. Multiplier(b))tomodify flow across the face.

You can set a constant transmissibility multiplier(BarrierTrans. Multiplier(b)) to be applied across a face for which theBarrier Attribute changes, or you can set up a table of barrierattribute changes for which specific multipliers can be applied.

For either choice, select an attribute for the Attribute forBarrier(a)and a constant forBarrier Trans. Multiplier(b).

To investigate what happens if there is no flow across sequenceboundaries, select Sequence Numberfor the barrier attribute andset the transmissibility multiplier to zero. To determine whathappens if there is not flow between sequences (for example,

between sequence 8 and 12,) select Tableas input and between 8and 12, apply a multiplier of zero.

5. To factor a fault zone into your calculations, select an attributefield forFault Zone Thickness (a) andFault Zone Permeability(b).These options assume that you have already constructed thenecessary attributes using the Fault Seal Analysis module inStratamodel. If StrataSim does not detect such attributes, you willreceive a warning message.

Fault Seal Analysis calculates the fault zone permeability andthickness and stores this information in the Attribute Model. These

calculations consider both the juxtaposition of reservoir andnonreservoir material in the fault zone and the composition andfabric of the fault rock. StrataSim picks up this informationdirectly from the Attribute Model and uses it to calculateTransmissibility Multipliers.

6. Click OKto close the Transmissibility Calculation dialog box.

7. Click OKto close the Three-Dimensional Variables dialog box.


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Setting Optional Variables

The optional three-dimensional variables allow you to constrain thepressure of flow potential for particular cells within your simulationmodel. You might want to do this for several reasons.

Suppose, for example, that you partitioned your entire StratigraphicFramework into several smaller simulation models. You may find ituseful to constrain the pressure on the periphery of one model by whatyou have already calculated using another model.

As another example, you may want to simulate aquifer influx of waterat a prescribed flow potential. Yet another example would be thecalculation of effective properties over a portion of the reservoir forwhich you may want to impose the following left-to-right flow, asshown in the following example.

To constrain the flow potential as shown above, use the StratamodelModel Operations. Put a high potential in cells in the first column andlow potential in cells in the last column. Set all other cells as null tosignal no constraint in these cells.

Sometimes the need for constraints can be clear, but it is not clearwhich constraint to use. Here is a simple rule you may find helpful:

If output from a previous StrataSim run is used as a constraint,

constrain the pressure. For all other cases constrain the flow potential unless you are

absolutely sure you have properly accounted for gravitationaleffects when you calculated the pressure constraint.

Flow

ProducingInjecting Cells

e t-to- g t ow

HighPotential

Low

Potential

Cells


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This rule helps to avoid the most common problem: that pressure isused when flow potential is intended. This confusion between pressureand flow potential is surprisingly widespread, for example, ininterpreting Darcys law. For a more thorough explanation, see AnExample of Misinterpreting Darcys Law on page 95.

Constant Pressure Constraint

You can assign constant pressure values to an attribute field usingModel Operations in Stratamodel. Using the rule stated above, youwould constrain pressure using pressures calculated from a previous

run. The constant pressure attribute would consist of the calculatedpressures in the cells that you wish to constrain and nulls in all othercells.

Constraints are imposed only at cells with nonnull values.

To set Constant Pressure Cells, follow these steps:

1. Click the Constant Pressure Cells Attribute Fieldbutton.

2. Select an attribute from the resulting list.

3. Click OK.

Definition of Reference Elevation

To input data correctly you should understand that reference elevation is equal tothe elevation at which the flow potential equals the pressure.


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Constant Flow Potential Constraint

You can assign constant flow potential values to an attribute field usingModel Operations in Stratamodel. The following figure shows anexample with a high flow potential on the left-hand side of the model, alow value at the right-hand side, and all nulls in between.

Pressure Distribution in an Onlapping Depositional Environment

To set Constant Potential Cells:

1. Click the Constant Potential Cells Attribute Fieldbutton.

2. Select an attribute from the resulting list.

3. Click OK.

Reference Elevation

You must set a reference elevation if you are using Constant PotentialCells. To set reference elevation

1. Click Reference Elevation Constant.

2. Enter the value of the reference elevation in feet.

3. Click OK.

Sequence Numbers Pressure Distribution

high flow potential

low flow

potential


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R2003.12 Setting Up StrataSim: Indicating Perforation 57

Indicating Perforation

You have the option to read in perforation interval information from awell model in the Well Model Attributes dialog box. If no data isavailable, the wells are assumed to be fully perforated along the lengthof the well. StrataSim assumes that there is no pressure drop (zero skin)between the well and the cells penetrated by the well.

You can input perforations in the well data files used to build a wellmodel. Any value greater than zero assigned to a depth intervalsignifies a perforation zone. We advise you to use the Discrete WellModel Calculation option for averaging perforations when building awell model.

Because of the nature of the discrete well model calculation, with somechoices of vertical layer resolution in the Stratigraphic Framework

model small perforation zones may not show up in the final well model.Distributing the perforation data using the nearest neighborinterpolation algorithm allows you to verify the location of theperforations at the well.

Perforations in Well Model

Calculations

GR Perf.

layer 3

layer 2

layer 1

layer 3

layer 2

layer 1

Well-logs Cell

GR = 30

GR = 20

GR = 40

not perfed!

perfed

perfed

After Well Model Build

To verify perforations, visualize in the attribute model

by using the nearest neighbor interpolation


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R2003.12 Setting Up StrataSim: Indicating Perforation 58

To read in perforation information, follow these steps:

1. Select Setup Well Model Attributes.

2. Select one of the well model names.

3. Select an attribute to assign to the selected well model, and clickOK.

4. Optional: Repeat Step 3 for any other well models you want to setperforations for.

5. Click OK.


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R2003.12 Setting Up StrataSim: Setting Fluid and Rock Properties 59

Setting Fluid and Rock Properties

Use the Properties Fluid and Rock Propertiesdialog to set upfluid and rock properties that deal with assumptions underlying

StrataSims flow algorithms that mobility and density ratios equal 1.The text at the left side of the page explains the formulas for relativepermeability, effective permeability, and mobility ratios.

As mentioned in the Introduction, StrataSim assumes incompressibleflow of oil as water. However, this dialog box allows you to specify

formation volume factors and the solution gas/oil ratio. This input doesnot affect fluids in the reservoir; it only relates reservoir volumes toproduced volumes. In other words, StrataSim does not simulate flow ofgas in the reservoir; it associates solution gas to produced oil, resultingin gas production.

K'r = end-point relative

permeability

Kr = relative

permeability

Sw = water saturation

Swr= irreducible water

saturationS0r= residual oil

saturation

K = permeability

= viscosityr = endpoint mobility

0

1.0

1.0

Relative

Permeability

k0

ro

Swr Sor

k0

rw

Water Saturation

Effective Permeability:

Unit End-point Mobility

Ratio:

Ke Kr K=r Kr =

MK'rw oK'ro w----------------- 1= =


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R2003.12 Setting Up StrataSim: Setting Fluid and Rock Properties 60

Using the Fluid and Rock Properties Dialog Box

To display and use the Fluid and Rock Properties dialog box, followthese steps:

1. Click Properties Fluid & Rock Properties.

If you change the default values for viscosity and end-pointrelative permeability, the change in the mobility ratio appears atthe bottom of the screen. If the mobility ratio is not equal to 1.0,when you clickOK, StrataSim forces it to that value by setting therelative phases to the average of the values for oil and water. To

ensure unit density, StrataSim uses the average density of bothphases.


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R2003.12 Setting Up StrataSim: Setting Interfacial Tension 61

2. To change the defaults, enter new values in the appropriate fieldsandmake sure you keep the Mobility Ratio close to 1.

3. StrataSim assumes that flow due to differences in fluid densities isnegligible compared to overall flow. So the program calculatesgravitational potential using the average density of the oil and

water phases. To change the default Densityvalues, double-clickin the field and enter a new number.

4. Enter a Formation Volume Factor.StrataSim assumes anincompressible flow of water and oil. This parameter relatesreservoir volume to stock tank volume. The default for this factoris 1.0.

5. Enter the estimatedSolution Gas/Oil Ratioby clicking in the

strata sim

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