NEW KEYWORDS AND OPTIONS ADDED TO IMEX 96.00 Input/Output Control
IMEX 96.00 has several enhancements that make the input output controls more flexible and user friendly. Display of the screen diary file can be changed to include additional well information. IMEX can now be run with the name of the data set specified through a command line argument (i.e. mx064.exe -f data1.dat). The root names of the output file, input .irf and .mrf files will automatically be the root name of the data file.
*OUTSRF, *WELL, *DOWNHOLE, *LAYER, *BLOCKP
Well layer records are no longer written to the SR2 files *WELL at surface and reservoir conditions. In order to reduce the size of .mrf files, only well records at surface conditions are written. The user can still write layer information at either reservoir and/or surface conditions using the keywords shown here.
*XDR
The binary (data) file may be written in external data representation (XDR) format as well as the binary format native to your platform. Use of XDR allows the SR2 binary file(s) to be written on one platform and read on another. For example, the SR2 files can be generated on a UNIX workstation server and then accessed with RESULTS or the Report Writer on a PC. If the SR2 is in XDR format, then the keyword "XDR" will appear near the top of the index file (IRF). XDR is a nonstandard option, and the source code is shipped with XDR disabled. Most executables shipped by CMG will have it enabled.
*OUTDIARY, *WELLSTATUS
These keywords specify that the number of producing wells, injecting wells, and shut in wells and the maximum changes of saturations and pressure will be written to the output-diary-file. The oil/gas/water production/injection rates will be written with up to 6 significant figures. The water-cut will be written with up to 3 significant figures.
*INTERRUPT, *RESTART-STOP, *STOP, *INTERACTIVE
These keywords indicate that when the user interrupts the simulation run by simultaneously pressing the "CTRL-C" keys or by typing "kill -2" followed by the process identification number (PID), one of the following user specified actions can take place:
1. Continue the simulation run
2. Finish the current timestep, write a restart record and stop the simulation.
3. Flush buffers, close files and stop the simulation run immediately.
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Use of this keyword prevents corruption of the .irf and .mrf files when aborting a simulation run and optionally writes a restart record before stopping.
Reservoir Description
*PVCUTOFF
This option allows the user to adjust the pore volume cut off value and controls the level at which a block will be set null due to a small pore volume. This option ensures that blocks with small pore volumes can be systematically removed from the simulation. Such small pore volume blocks can hinder convergence and should not remain in a simulation.
*NETGROSS
This option allows the input of net-to-gross ratios which are used to modify the porosities and permeabilities in the I and J directions. The net-to-gross ratios are used as multiplication modifiers.
Rock-Fluid Properties
A number of options for smoothing both user input relative permeability and capillary pressure data. In addition, these data can also be generated using standard power law correlations.
*SMOOTHEND, *QUAD, *CUBIC, *POWERQ, *POWERC
This optional keyword indicates the type of smoothing that is to be used at the end points for the interval between kr = 0 and the first nonzero value of kr
for both krw and krow (krg and krog). The keyword may be followed by subkeywords that specify the type of smoothing to use.
For the subkeyword *QUAD, a quadratic smoothing is used. For *CUBIC, a cubic smoothing is used. If no smoothing has been specified, then linear interpolation is used. For *POWERQ and *POWERC end point smoothing is done using power law if the exponent is between 1.5 and 4.0. Otherwise, for *POWERQ, quadratic is used and for *POWERC, cubic is used for end point smoothing.
Please see the *SWT or *SGT (*SLT) entry in this manual for more details.
*SMOOTH, *ALL, *ALLINT, *ALLIN, *ALLPL
This option smoothes the entire relative permeability table and generates a new table consisting of smoothed, equally spaced values. One or all saturation dependent properties in the table may be smoothed based on user controlled specifications. The data may be smoothed using a power law correlation, linear interpolation or a combination of the two. Please see the
*SWT or *SGT (*SLT) entry in this manual for more details.
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Numerical Methods Control
*RELAX, *ACC, *GAS
The *RELAX *GAS enables the gas-saturation under-relaxation option.
This option can lead to faster convergence for simulations where the overall pressure in the reservoir is declining and gas is being liberated due to the pressure falling below the bubble point. This option prevents the gas from disappearing in a grid block for three Newtonian iterations. If IMEX predicts that gas in a grid block will disappear for more than three iterations, only then will the gas be allowed to disappear.
The *RELAX *ACC option performs over-relaxation of the accumulation term. This normally improves model performance.
Well Management
Well management has several improvements and bug fixes. Some new options have also been added.
*ON-TIME
This new option allows the input of fractions for all wells or selected wells which specify the fraction of the simulated time during which the well is on-line and actually in operation. If a well is assigned an on-time fraction less than one, the rates reported (the "averaged" rates) are less than the rates which apply when the well is actually in operation (the "instantaneous"
rates). The user should enter well constraints (such as BHP, WHP and rate constraints) which correspond to INSTANTANEOUS rates; reported BHP and WHP values will correspond to the instantaneous rates. Reported rates and cumulative volumes will, however, be the averaged values. If the *ON-TIME keyword does not appear in the data set, the default value of one is applied for the on-time fraction and the simulation is unaffected by the introduction of the option.
*MONITOR, *MIN or *MAX, *WHP or *BHP
It is now possible to enter maximum BHP and WHP values as monitored constraints for producing wells; please see the entry for the *MONITOR keyword in this manual for more details.
It is also now possible to specify maximum lift gas rates for wells under the
*GLIFT *OPT option; please see the *GLIFT entry for details.
When entering wellbore hydraulics tables under the *PTUBE keyword, it is now possible to direct the simulator to supply missing values by interpolation or extrapolation from other values in the same row of the table by entering
*EXTP in the place which the missing number would normally occupy;
please see the *PTUBE entry in this manual for more details.
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*MINOIL, *MINGAS, *AUTO-OPEN
An *AUTO-OPEN action has been added to the *MINGAS and *MINOIL constraints under the *GCONM group monitoring keyword. This action allows wells in a particular group which have *AUTODRILL status to be opened automatically when the group's gas or oil production rate falls below the specified value. Please see the *GCONM entry in this manual for more details.
*TURB, *QUAD
This option is used for calculating the drawdown pressure for high gas rate wells. These keywords specify the use of quadratic inflow performance and a rate dependent turbulent skin factor. Please see the *PERF entry in manual for more details.
*WELLINIT, *CHANGE, *ITER
This option allows the user to specify whether the bottomhole pressure value for all wells running on a rate constraint, drawdown constraint or an
implicitly imposed wellhead pressure constraint should be reinitialized 1) only after well changes or 2) after each Newtonian iteration. This keyword also determines whether wells operating under a *WHP *IMPLICIT constraint are checked for shutting in at the Newtonian or timestep level.
Use of the *ITER option, especially for high permeability cases, usually results in rapid convergence of the well equations by reducing the total number of Newtonian iterations. For cases with low permeability and/or high compressibility, this option may reduce the total number of Newtonian iterations and reduce the CPU time.
OLD OPTIONS NO LONGER SUPPORTED BY IMEX 95.00
The *UNDER-RELAX *GAS option is no longer supported by IMEX 95.00. Use the
*RELAX *GAS option instead.
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