INTRODUCTION TO CMG- IMEX

BLACK OIL MODEN

• Simulator Data Organisation• I/O Control Section• Reservoir Section• Components Section• Rock-Fluid Section• Initial Conditions Section• Numerical Section• Well & Recurrent Section

Presentation Outline

Simulator Data Organisation

• Basic file extensions

- *.dat – simulator input file- *.inc - additional include files- *.out - File output by simulator (ASCII)- *.irf - Header file output for graphical post processing (index results file)- *.mrf- Binary data file containing simulator results (main results file)

Simulator Data Organisation

• Additional file extensions

- *.rrf – restart results file, output at user defined intervals to allow simulator to restart from that point beyond- *.err - error file- *.ses - Template file for Graph- *.3tp - Template file for 3D results- *.fhf - Historical data file - *.log - Diary output, time step summary, Convergence summary

Simulator Data Organisation

• The *.dat file contains several data sections in the following order

- I/O Control section- Reservoir Section- Components Section- Rock-Fluid Section- Initial Conditions Section- Numerical section- Well and recurrent data section

Simulator Data Organisation

• I/O Section• Controls for filenames used• Dimensioning statements• Unit System• Controls for frequency and content of output

*TITLE1 ‘Example Problem’*TITLE2 ‘March-2007'*CASEID 'History'*INUNIT MODSI*WSRF WELL 1*WSRF GRID TIME*WSRF SECTOR TIME*OUTSRF WELL LAYER NONE*OUTSRF RES ALL*OUTSRF GRID SO SG SW PRES DATUMPRES*WPRN GRID 0*OUTPRN GRID NONE*OUTPRN RES NONE

Simulator Data Organisation

• Reservoir Description Section- Description of geological

framework- Type and dimension of grid- Spatial location- Layering of flow units- Faults / Transmissibility - Phi, K

GRID VARI 45 70 3KDIR DOWN DI IVAR 45*150DJ JVAR 70*150DK ALLInclude 'gross.arr'DTOPInclude 'top.arr'NULL ALLInclude 'act.arr'NETPAY ALLInclude 'net.arr'POR ALLInclude 'por.arr'PERMI ALLInclude 'permx.inc'PERMJ EQUALSIPERMK EQUALSITRANSI *IJK10:10 1:25 1:3 0TRANSK *IJK1:45 1:75 1:3 0

0 1,000 2,000 3,000 4,000 5,000 6,000

0 1,000 2,000 3,000 4,000 5,000 6,000

-5,0

00-4

,000

-3,0

00-2

,000

-1,0

000

-5,000-4,000

-3,000-2,000

-1,0000

0.00 0.25 0.50 0.75 1.00 miles

0.00 0.50 1.00 km

File: ADBv ariant_recommended.irfUser: 070418Date: 6/12/2008

Scale: 1:41685Y/X: 1.00:1Axis Units: m

2,249

2,273

2,298

2,322

2,346

2,370

2,395

2,419

2,443

2,468

2,492

SIMULATION OF LAKWA TS1Grid Top (m) 0.00 day K layer: 1

Simulator Data Organisation

• Fluid Model Section- Type of fluid to be modeled

• Black oil• condensate• gas water

- PVT description- FVF, Rs, Bg, Uo, Ug, Co- Surface phase densities

MODEL BLACKOIL TRES 130PVT BG 1 *** 297 Block

** P RS BO BG UO UG CO

20.00 44.0 1.3594 0.061337 0.3570.0106 0.00038460.00 99.2 1.5849 0.019424 0.2410.0119 0.000384100.00 151.3 1.7755 0.010905 0.1760.0131 0.000384120.00 180.5 1.8810 0.008946 0.1630.0138 0.000384

DENSITY OIL 806.2DENSITY GAS 1.525 ** kg/m3

REFPW 1.03323DENSITY WATER 1000.BWI 1.02CW 5.3e-05 *** 1/kg/cm2VWI 0.25 ** in cpCVW 0CVO 33e-05 ** Oil visc correction above pb

• Rock-Fluid Section- Similar rock types are grouped together- Rel perm tables- Cap. Pressure curves- Hysterisis

Simulator Data Organisation

ROCKFLUIDRPT 1

SWT***Sw Krw Krow Pcow

0.2000 0.000 1.000 0.00.3120 0.004 0.458 0.00.4240 0.020 0.167 0.0 0.5920 0.082 0.015 0.00.7600 0.200 0.000 0.01.0000 1.000 0.000 0.0

SGT**Sg Krg Krog Pcog

0.0000 0.0000 1.00000 0.00.0200 0.0000 1.00000 0.00.1620 0.0064 0.40813 0.00.3300 0.1000 0.06161 0.00.3860 0.1728 0.02505 0.00.5540 0.5832 0.00009 0.00.6100 0.8000 0.00000 0.0

Simulator Data Organisation

• Initial conditions section- Allocation of saturation/

pressure- Vertical equilibrium- Fluid contacts- Reference pressure/depth- completes static description- Fluid-in-place can be computed

SWCON ALLINCLUDE 'gs12a_swcon.inc'

SWCRIT ALLINCLUDE 'gs12a_swcrit.inc'

SORW ALLINCLUDE 'gs12a_sorw.inc'

SORG ALLINCLUDE 'gs12a_sorg.inc'

INITIALVERTICAL DEPTH_AVE WATER_OIL_GAS EQUIL

REFDEPTH 3250REFPRES 340.0

DWOC 3420 *** 297 BlockDGOC 2800

DATUMDEPTH 3250

PB CON 150

Simulator Data Organisation

• Numerical section- matrix soln method- iteration convergence limitscan be tuned- DTMAX, DTMIN

NUMERICALRUNDATE 1993 4 1*DTMAX 31.0 *DTWELL 1.0 *NORM *PRESS 1000 ** Normal maximum change per timestep*NORM SATUR 0.2

GROUP 'Group-297' ATTACHTO 'Field'GROUP 'Group-205' ATTACHTO 'Field'

WELL '138' ATTACHTO 'Group-205'PRODUCER '138'OPERATE MAX STO 100. CONT**$ rad geofac wfrac skinGEOMETRY K 0.1079 0.37 1. 5.0PERF GEO '138'**$ UBA ff Status Connection 24 46 2 1. OPEN FLOW-TO 'SURFACE' REFLAYER 24 46 3 1. OPEN FLOW-TO 1

Simulator Data Organisation

• Recurrent Data Section- Group hierrarchy- Well definitions- Perforation definition- Operating guidelines/monitoring controls- historical prodn data

I/O Control Section

I/O Control Section

• I/O Control• applied throughout run• report variables listed

• Well & Recurrent Section• Applied from that point onward• Typically alters output freq. or provides specific report times *WRST TNEXT

I/O Control Section

Check to select the output in SRF and OUT file

Restart Files

• *WRST initiates output of the restart information

-Can be used in I/O section or wells section

• Builder I/O section allows selection of restart points

Restart Files

• REWINDable restarts

- usually restart information is held in .irf/.mrf files - *REWIND causes an .rrf file to be created - *REWIND 3

– only the last three restarts will be preserved

- saves time and space

Using Restart Files

• Keywords required * FILENAME INDEX-IN ‘d:\ABC\history.dat’ (This must be the first keyword in the file) * RESTART 132

• Add these to the original run and save the new file as a different name

• No other changes are required - Any data before the restart data will be skipped

Reservoir Section

Simulation Model Gridding

• Types of grid and data input• Structural data• Property data and modification• Sectors• Problem grids and geology

Gridding

• Grid Types- CART- VARI- CORNER- RADIAL

* KDIR UP/DOWNI

J

K

I

J

K

K=1 at the top K=1 at the bottom

Forms of Geological Data

• Data types accepted by builder•Scatter data points (well data)•Contour maps o f 2D surface

- Sets of connected points forming line with value, may contain faults and well locations- Atlas Boundary, WINDIG, ZMAP,CPS-3

• Mesh maps of 2D surface- Regular, orthogonal grid of data- CMG, ZMAP GRID, CPS-3

• RESCUE formats (Petrel, Landmark, Roxar)

Specifying Property

• Select Property and layer, PVT/RTYPE/Sector• Can use Value ; Map ; Formula

Specifying Property

Array Property Calculator

• User enters formula to define property arrays from other arrays-Logic, arithmetic and logarithmic functions

• Have an easy to use interface for constructing formulas

• Properties once calculated can be graphically edited and saved to MOD array

Sectors

• Sectors define individual reporting areas-FIP, Prodn/Inject accounting

• Defined either by- Numbered array- Distinct sector name

• Report to text or graphics output files

Components Section

Reservoir Fluids

• Black Oil• Volatile Oil• Retrograde Gas Condensate• Wet gas• Dry gas

Experimental Analysis

Three main, and one optional, experiments required:

• Flash Expansion – to determine Pb

• Differential Liberation – to determine, Bo, Rs, Bg, Muo, Mug

• Flash separation – to modify diff lib data to match field separator conditions

• Swelling Test – to provide properties when gas is injected

IMEX Fluid Model Types

• BLACKOIL - 3 Phases O W G• OILWATER

- 2 Phases O W• MISCG

- 4 Phases O W G S• MISNCG

- 3 Phases O W G (same gas for injection)• POLY

- 4 Phases O W G P• GASWATER

- 2 Phases G W• GASWATER_WITH_CONDENSATE

- 3 Phases O W G, but O can vapourise gas phase

Black Oil PVT

• PVT data is enetered in tabular form

• Enter Rs, Bo, Eg, Uo, Ug as functn of pressureRs - Soln GORBo - Oil FVFEg/Bg - Gas expansion factor/Gas FVFUo - Oil ViscUg - Gas Visc

• IMEX allows both- direct PVT input *PVT and *PVTG- diff lib data *DIFLIB and *PVTG

- requires flash separator Pb, Bo and Rs

IMEX Conventions

• PVT table describes saturated behaviour only

• Compressibility used to define undersaturated behaviour

• Can supply Co within tables or as separate entries

• *CO describes undersaturated oil behaviour

• Can have different Co values for different Pbub

PVT using Correlations

PVT using Correlations

• Main properties which are determined:- Pb, Rs, Bo, Bg, density, Co, Viscosity

• Correlations are particular to specific areas• Some of the more widely used correlations

Standing Lasater Vasquez-Beggs

Glasso Marhoun

Pb, psia 130-7000 48-5750 15-6055 165-7142 130-3573

Temp, F 100-258 82-272 162-180 80-280 74-240

FVF 1.024-2.15 1.028-2.226 1.025-2.588 1.032-1.997

Rock-Fluid Section

Rock-Fluid interaction

• Relative permeability• End Point Scaling• Capillary Pressure• J Function• Wettability• Hysteresis• Non-Darcy Flow

Builder Functionality

• Builder Provides-Rel Perm curve generation from end point data

-End point scaling

-Number of smoothing functions

-Ability of QC and average Kr, PC data

-Graphical editing

Relative Permeability

• Usually two-phase data determined*SWT : Sw, Krw, Krow*SLT : Sl, Krg, Krog*SGT : Sg, Krg, Krog

• Capillary pressure (drainage and imbibition can be entered

• Critical and connate points can be scaled• Three phase measurements are very

difficult, correlations are used

Relative Permeability

Relative Permeability

• Usually simulators use Stone’s Model for generating 3 Ph relperm from

2 phase relperm data• Stone-1 & 2 are very popular methods• Fits measured data• Stone-2 is default• Other models also available

- Linear Isoperm- Segregated model

Hysteresis

• Hysteresis more pronounced in non-wetting phase

• Sg, So, Pcog, Pcow modeled

Initial Conditions Section

Reservoir Initialisation

• Assignment of saturation and pressure profiles- Can be done automatically assuming Gravity- Capillary equilibrium

- Block Centred- Depth Average

- Can be input manually (user input)

• Multiple regions (must have separate PVT)

Reservoir Initialisation

• Automatic allocation of vlaues requires- datum pressure and depth- WOC and/or GOC- contacts (Pc at defined values, default=0)

• DATUMDEPTH- reporting pressures in output

• Density data used for pressure profile• Capillary data for saturation profile

Reservoir Initialisation

Numerical Section

• Default Numerical parameters are usually sufficient

• No changes are required normally

• Iteration routine fails to converge- Take smaller timesteps – smaller DTMAX or - reducing changes/timesteps *NORM *PRESS and/or *NORM *SATUR- Increase iterations ITERMAX - Increase degree of factorisation *SDEGREE- This increase memory requirments

Numerical Tuning

Numerical Tuning

• Large number of time cuts :- Check PVT/Rock Curves for non-linearities- Check that grid and other properties are properly specified- Check the well constraints MAX BHP, MIN BHP- Check for small pore volumes- Increase Newton Cycles- Increase no. of time cuts *NCUTS

• Very small blocks can cause serious oscillations when connected to large blocks

• Use PVCUTOF to null out small PV blocks

Well and Recurrent Section

Well and Recurrent Data

• Section starts with *RUN keyword followed by *DATE

• Once start date set in builder can only change in text editor

• Simulation advances using *DATE or *TIME or both

• Static data can be altered with time

- I/O keywords can be inserted to produce output at specified dates

- can also add LGRs

- TRANS

- RTYPE

- Relperm endpoints

• The following is a complete description of a well

*WELL

*PRODUCER or *INJECTOR

*PWELLBORE or *IWELLBORE (only if WHP calculation is required)

*INCOMP (only for injectors)

*OPERATE (oil rate, liquid rate etc)

*MONITOR (watercut, GOR, BHP)

*GEOMETRY (well radius, skin etc)

*PERF

• Modifiers

*ALTER or *TARGET

Well Keyword description

• The well model is controlled by 2 dependent variables

-Well pressure and well flow rates

• The basic equation relating well inflow to pressure is :

Wells in Simulation

PWIQ jj (j=o, w, g)

Sr

r

KKhWI

w

ej

rjj

ln

12

Where,

BHPBlock PPP

Wells in Simulation

• Total inflow for a production well is :

)( PWIQ jionsallconnectj

• SET PI allows fixed WI value from well test or multiplier

to

be applied for whole well at a given time

• IMEX has several ways to allocate production to multiple

layers

- Define individual WI directly (PERF WI)

- Using grid block geometry (PERF GEO or KH)

Wells in Simulation

• The GEOMETRY keyword allows

- grid penetration direction

- well radius

- Geofac (used in re calculation)

- Wfrac (multiplier to account for non 360 deg flow)

- Skin

Wells in Simulation

• BHP is calculated at a defined depth

- Default datum is centre of first defined perf

- Otherwise by adding *REFLAYER to completion in

*PERF

- can also specify a BHP datum depth *BHPDEPTH

- default mobility weighted fluid density is used

• LAYERIJK

- well can be completed in several directions

- *GEOMETRY allows only one direction

• LAYERXYZ

- Based on well trajectory (by builder)

Well Control

• Wells can be controlled by either rate or pressure limits

• one must be specified, so that other can be derived

• Many limits can be set but only one can be in control at

any given time

- Multiple *OPERATE can be defined

- Most limiting one actually controls the well

- *ALTER changes first defined *OPERATE

constraint

- *TARGET changes any defined constraint

- Re-defining *OPERATE resets all earlier settings

• *MONITOR/PENALTY keyword can be used for well

management

Well location Options

• Builder will calculate well completion blocks using these

methods:

- X, Y of a well

- Import well deviation data

- can also specify well blocks using point and click

- Typing of block address

• Deviation data allows more accurate inflow description

*LAYERXYZ

Well Group Controls

• IMEX provides FIELD, PLATFORM, GROUP , WELL

hierarchical control

•FIELD

- PF1

-GROUP-1

-W1,W2, W3.....

-GROUP-2

-W5, W6, W7…..

-PF2

-GROUP-3

-W8, W9, W10….

-PF3

The Hierarchical Tree

• Always one ‘Default-Group’ is present

• Attached to “FIELD”

• Any well not attached to any group will be allocated to

default group

• Groups have separate injection and production controls

-GCONP, GCONI

• Cannot have both wells and groups attached to group

• Two levels of groups can exist between FIELD and

WELLS

Group Controls

• Rate, GOR and water cut constraints at any level

-Force simulator to honour facilities constraint

• Voidage replacement

- Pressure maintenance

- Recycling of produced water or gas

- Recycling needs both producers and injectors in

same group

• Automatic well re-completion, opening, shutting or

plugging to

defined levels• Assign/Re-assign platform, groups, wells at any time• Well can be attached to only one group at a time• Group targets allocated to wells/groups based on well/groups instantaneous potential

Aquifer - Analytical

• Analytical aquifers are mathematical equations connected to reservoir blocks to replicate water influx

• Fetkovich- Models finite aquifer without use of influence functions

• Carter Tracy- Pressure at external boundary does not change- Infinite acting by default- Influence table control water influx for finite representations

• Gravity effects not accounted in analytical models-Hence bottom aquifer may over predict water influx

• Direction of flow *AQLEAK- Default is only inflow allowed (no outflow on repressurisations)- *ON allows flow back into aquifer

Aquifer - Analytical

• Use R ratio to change strength (ratio of auifer radius to

reservoir radius)

• Very large aquifers can also be represented by constant

pressure wells

• Connect aquifer to water filled blocks

• Large volume water cells can be placed between

analytical aquifer and reservoir

• Can also apply volume multipliers to water cells (use

sensible values or it may create convergence problems)

Other capabilities

• Modeling Naturally fractured system (dual

porosity/permeability)

• Hydraulic fractures

• Local Grid Refinements

• Fault modeling

• Vertical flow modeling