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WHAT’S NEW IN IMEXTHREE-PHASE, BLACK-OILRESERVOIR SIMULATOR

VERSION 2013

IMPORTANT CHANGES IN IMEX 2013 AND IMEX 2012.10

SIMULATOR CHANGES

Initialization Regions Separate from PVT Regions Initialization regions may be specified using the *NREGIONS and *ITYPE keywords. Previous versions of IMEX linked PVT regions to initialization regions. Thus one PVT region was required for each initialization region. This is no longer required. Older data sets are unaffected.

Rock Compaction Table Reassignment in Recurrent Data The *CTYPE value (compaction table number) of gridblocks can now be reassigned in recurrent data. This allows the user to realistically model processes where permeability modification vs. pressure behavior is added later in a run. Hydraulically fracturing and introducing fracture conductivity vs. pressure behavior in a new well partway through a simulation is an example of this. Please see the manual as some restrictions apply to the use of this feature in recurrent data.

Solver Technology Improved Parallel Performance

Improvements to the implementation of parallelization in IMEX have allowed the Simulator to run more efficiently on larger number of threads on Shared Memory Processors.

Separate Graphics/Restart SR2 files (*RESTART_SR2 or Command Line -restart_sr2)

We have changed the default behavior when writing out SR2 graphics and restart data and have added a keyword and a command-line option to control if graphics and restart information in the sr2 files are combined or separated, for both input and output.The new default ‘*RESTART_SR2 *SEPARATE’ (-restart_sr2 separate) separates graphics and restart data. ‘*RESTART_SR2 *MAIN’ (-restart_sr2 main) combines graphics and restart data. Combined or separated SR2 files must be kept consistent between initial and restart runs. The new IMEX default is to use the *SEPARATE option as this option requires less disk space and take less CPU time for output due to writing the graphics data in single precision while writing restart data in double precision. The *MAIN option needs to write both graphics and restart data in double precision to maintain restarting accuracy. Please see the *RESTART_SR2 keyword in the IO Control Section for details on file naming conventions.

Other New Keywords Pressure vs. Depth Table (*PREST)

During non-equilibrium initialization, it is possible to assign block pressures using a table of reservoir pressures vs. depth for each initialization region. Previous versions of IMEX required the user to enter the entire pressure array. This option simplifies non-equilibrium initialization.

WHAT’S NEW IN IMEX 2013 1

Output of Well PI Based on an Approximation of the Well’s Drainage Pressure (*OUTSRF *WELL *PDRAIN, *PDRAIN-METHOD)

Specification of *OUTSRF *WELL *PDRAIN initiates a more involved calculation of a well’s productivity index based on a flexible approximation of well drainage area/pressure. *PDRAIN-METHOD controls how the approximate drainage pressure is calculated.

Change the Minimum Oil Saturation Initially Placed in Each Block when Using API-Tracking Option (*APIMINSO)

Using the API-Tracking Option, it was possible for the model not to initialize blocks with a small amount of oil (to prevent formulation issues) when using the *DEPTH_AVE option. This issue has been eliminated in this release. In addition the initial minimum oil is now controllable using the *APIMINSO keyword in the Initialization Section. *APIMINSO is set to 1.00e-04 by default.

New Restarting Features (*RESTART *RESDATE/*RESTART *RESTIME)

It is now possible to specify a restart at a specific date or time in addition to a timestep number. The *RESDATE “date” and *RESTIME “time” keyword can be used in addition to *RESTART “num”

Template Data Set Changes Added mxflu006.dat to demonstrate *PREST table inputAdded mxsmo060.dat to demonstrate initialization regionsAdded mxsmo061.dat to demonstrate *CTYPE in recurrent dataAdded mxwwm055.dat to demonstrate *DRILLTAdded mxwwm056.dat to demonstrate gas lift triggersAdded mxwwm057.dat to demonstrate new Sector triggersAdded mxwwm058.dat to demonstrate *AVRGTIME in triggersAdded mxwwm059.dat to demonstrate *OPERATE-HISTAdded mxwwm060.dat to demonstrate *WCUTBACK in *OPERATEAdded mxwwm061.dat to demonstrate *PDRAIN well PI output option

Data Incompatibilities with Previous Versions of IMEX None.

WELL MANAGEMENT CHANGES *OPERATE-HIST, *ALTER-HIST

The *OPERATE-HIST keyword signals that a well’s operating constraints entered using the *OPERATE keyword are historically observed rates and allows the well to operate under history matching mode. Under history matching mode, it is possible to specify the reservoir fluid rate using the sub-keyword *RSV. This converts the STC fluid rates entered on the *OPERATE keywords to reservoir fluid volumes. The reservoir volume (based on current reservoir conditions) is produced. *ALTER-HIST allows the modification of the historically observed flow rates.

WHAT’S NEW IN IMEX 2013 2

*OPERATE *WCUTBACK

A new type of well operating constraint has been introduced. The *WCUTBACK sub-keyword of *OPERATE specifies that a well will run on a reduced rate target of a specified control phase whenever it violates a well ratio constraint (example GOR, WOR etc.) or maximum/minimum well block pressure constraint.

*WTINCR, *GCONPINCR, *GCONIINCR

*WTINCR allows the modification of any previously specified well constraint by applying an incremental value to that constraint. *GCONPINCR and *GCONIINCR allow the same incremental modification for production and injection groups.

*AVRGTIME in Triggers

The *AVRGTIME sub-keyword of *TRIGGER can be used to specify the time period over which a moving average of a quantity (such as rate) is calculated.

Gas lift Triggers

The *ON_WELL and *ON_GROUP triggers now include gas lift based triggers.

*Sector Trigger Enhancements

The *ON_SECTOR keyword allows test conditions to be applied to a sector. Minimum and maximum sector pressure and sector saturations have been added to *ON_SECTOR test quantities

*PDRAIN-METHOD

The *PDRAIN-METHOD keyword allows the user to choose how the approximate drainage area is to be calculated when *OUTSRF *WELL *PDRAIN output is selected.

GRID CHANGES *TRANSMULT

The *TRANSMULT keyword allows the specification of the action to take when encountering successive transmissibility multipliers. *REPLACE (the default) allows the current multiplier to be replaced by the new multiplier. *ACCUMULATE allows the current multiplier to be multiplied by the value just read in. *TRANSMULT may be altered in recurrent data to change the default *REPLACE option to *ACCUMULATE.

Inter Region Transmissibility Multipliers

*INTER_REGION_TM specifies the inter region transmissibility multiplier between two adjacent regions defined by the *TRANS_MULT_REGION keyword. This option can be used to reduce or eliminate flow between two regions.

*CRNCON_NODE

A NODE based corner-point grid option has been implemented in CMG simulators. Builder can be used to convert existing corner point grids to NODE based grids. Alternatively the keyword *CRNCON_NODE or the command line option ‘-crncon_node’ allows the user to have the simulator internally convert an existing corner point grid to its NODE based counterpart. This option may speed up the grid generation part of a simulation considerably at the cost of extra memory. NODE based grids have been found to be very efficient for grids with a large number of refined cells (for example: hydraulically fractured wells modeled using the LS-LR-DK technique).

WHAT’S NEW IN IMEX 2013 3

Bugs Fixed All of the problems below have been corrected in IMEX 2013.10 since the release of IMEX 2012.10

• Corrected a problem with Fine Integration when unusual ordering or the corner point grid was encountered.

• Corrected an error in the HFP model where negative skin could cause the dynamically calculated well PI to become negative.

• Corrected a problem with restarts and SWINIT when used with the BLOCK_CENTER initialization option.

• Corrected a problem where compaction tables could extrapolate pressure dependent permeability’s to a value which was so low that an existing connection between blocks was eliminated, resulting in a run error. Permeability multipliers are now limited to the lowest value in each table.

• Corrected a problem with DEPTH_AVE initialization and endpoint scaling which could result in small oil saturations in the gas zone when there should be none (GASZONE NOOIL) or small oil saturations in the water zone when there should be none.

• Corrected a problem in calculating the average density of a well layer when the total mobility of that layer equals 0.0.

• Units in Seawater scaling table (SCLDPS) are incorrectly described in the User Manual. The units of scale deposited per water production should be entered in lb/STB when using FIELD units, not lb/FT3.

• The Well Echo of scale deposited per Perf-Length (‘Scale/Perf-Length’) undergoes unit conversion from SI units for the first layer only. Every other layer is output in SI units.

• The Seawater Scale option was incompatible with compaction tables. Well productivity was not being recalculated when scale reduced well permeability.

• The SCALING-STARS option would not properly determine SOIRG unless it was input in an array.

• SOIRG input without the SCALING-STARS keyword did not automatically turn on the SCALING-STARS option.

• Using the API-Tracking Option, it was possible for the model not to initialize blocks with a small amount of oil (to prevent formulation problems). This has been corrected when using the DEPTH_AVE option. The initial minimum oil is additionally controllable using the APIMINSO keyword in the Initialization Section. APIMINSO is set to 1.00e-04 by default.

• Well Rates were not written out to the SR2 by default, instead they were calculated from the cumulative volumes. Occasionally this would result in small differences between rates from the simulator log files and from RESULT Graph. Well Rates are now written out by default.

WHAT’S NEW IN IMEX 2013 4

• *OUTSRF *WELL *WELLPI documentation was missing from the manual.

• *OUTSRF *WELLRATES documentation was missing from the manual.

• There was a possibility that output to SR2 would be incorrect when TRANSI/J/K orPERMI/J/K modification in recurrent data changed parallel domain ordering during a run. The workaround was to run not using the –jacpar command-line switch, instead using the –doms command-line switch. This only effects grid output, the simulation was correct.

• Corrected a problem with FLUX-SECTORS when recurrent refinements were added.

• Corrected a misleading error printout problem in FLUX_SECTORS when FLUX_SECTORNAMES is not followed by FLUX_ISECTOR.

• Renamed sub-keyword TARGET under GCONP/I for group control to GTARGET

• A bug using *PMAINT *PMTARG with the modified SI units for input data (*INUNIT *MODSI) in IMEX was corrected. IMEX interpreted the pressure as kPa rather than kg/cm2.

• A bug where The Grid Module fails to make a connection through badly formed but pinched-out blocks was corrected.

• Improvements to the detection of overlapping refinement and an accurate message were implemented.

• Improvements for hybrid grid connection for corner point grids were implemented.

WHAT’S NEW IN IMEX 2013 5