IMEX currently provides seven different ways to initialize the reservoir.
1. *USER_INPUT
2. *VERTICAL *BLOCK_CENTER *WATER_OIL 3. *VERTICAL *BLOCK_CENTER *WATER_GAS 4. *VERTICAL *BLOCK_CENTER *WATER_OIL_GAS 5. *VERTICAL *DEPTH_AVE *WATER_OIL
6. *VERTICAL *DEPTH_AVE *WATER_GAS (*TRANZONE) 7. *VERTICAL *DEPTH_AVE *WATER_OIL_GAS
In the following each of these options will be described:
*USER_INPUT:
This option is used to directly specify the values of the pressure and saturation for each grid block. The following keywords, which must be located in the Initial Conditions section, are used with this option.
a) USER_INPUT b) *PRES, (pressure)
c) *SW (water saturation, need not be entered if using the two phase model,
*MODEL *OILWATER)
d) *PB or *PBT (bubble point pressure) e) *PDEW or *PDEWT (dew point pressure
*GASWATER_WITH_CONDENSATE or *VOLATILE_OIL models) f) *PBS (solvent bubble point pressure, if using any of the pseudo-miscible
models)
g) *SO (oil saturation, need not be entered if using the two phase model,
*MODEL *GASWATER) Example:
*INITIAL
*USER_INPUT
*PRES *CON 3400.0
*PB *CON 2500.0
*SO *CON 0.5
*SW *CON 0.2
Previous to version 93.10 this option was invoked using the keywords *VERTICAL *OFF.
These keywords are still accepted by IMEX.
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Using this option may cause a nonequilibrium initial distribution of fluids which may result in large fluid flow during the first few timesteps. This option is typically used when a simulation is started not from initial conditions but from another simulation run.
*VERTICAL *BLOCK_CENTER *WATER_OIL or
*VERTICAL *BLOCK_CENTER *WATER_GAS or
*VERTICAL *BLOCK_CENTER *WATER_OIL_GAS
These options are used to perform gravity-capillary equilibrium calculations based on the values of the water-oil, oil-gas, and water-gas contacts and the value of the pressure at a reference depth. The saturations for the entire grid block are set equal to their values at the grid block center.
*VERTICAL *BLOCK_CENTER *WATER_OIL is used for reservoirs containing only water and oil phases. The value of the water-oil contact depth is specified using the keyword *DWOC.
*VERTICAL *BLOCK_CENTER *WATER_GAS is used for reservoirs containing only water and gas phases initially. The value of the water-gas contact depth is specified using the keyword *DWGC. *VERTICAL
*BLOCK_CENTER *WATER_OIL_GAS is used for reservoirs containing water-oil and gas. The water-oil contact and gas-oil contact depth are specified using the keywords *DWOC and *DGOC.
*GASWATER and *GASWATER_WITH_CONDENSATE models must be initialized using either the *VERTICAL *BLOCK_CENTER
*WATER_GAS* or VERTICAL *DEPTH_AVE *WATER_GAS initialization option. Use of the *DWGC keyword is required with the
*WATER_GAS initialization option.
The following keywords, which must be located in the Initial Conditions section, are used with these options.
a) *REFDEPTH (reference depth)
b) *REFPRES (pressure at reference depth) c) *PB or *PBT (bubble point pressure) d) *DWOC (water-oil contact)
e) *DWGC (water-gas contact)
f) *DWOC and *DGOC (water-oil and gas-oil contacts)
g) *PDEW or *PDEWT (dew point pressure – Condensate models only)
Optionally the user can define the initial water saturation along with all of the above by using the *SWINIT option. This option attempts to adjust/alter Pcow curves to allow user defined water saturations to be in gravity-capillary equilibrium.
Care has to be taken when this option is employed, nonzero Pcow curves must be used and reasonable values of saturation must be entered. Highly altered Pcow can significantly effect other aspects of the model. Please see the *SWINIT keyword for more details.
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Example:
*INITIAL
*VERTICAL *BLOCK_CENTER *WATER_OIL_GAS
*PB *CON 2500.0 **bubble point is constant **throughout the reservoir.
*REFDEPTH 900.0
*REFPRES 3000.0
*DWOC 1250.0
*DGOC 788.0
For the above *BLOCK_CENTER options, the value of the saturation assigned to a given grid block is given by the value of the saturation at the grid block centre. In this way, for example, if a grid block has its block center slightly below the water-oil contact depth, the water saturation assigned to the block will be equal to the value of the water saturation below the water-oil contact.
*VERTICAL *DEPTH_AVE *WATER_OIL or
*VERTICAL *DEPTH_AVE *WATER_GAS (*TRANZONE) or
*VERTICAL *DEPTH_AVE *WATER_OIL_GAS
These options are also used to perform gravity-capillary equilibrium calculations based on the values of the water-oil, oil-gas, and water-gas contacts and the value of the pressure at a reference depth.
In contrast to the *VERTICAL *BLOCK_CENTER option the value of the saturation assigned to a given grid block is the average over the grid block volume of the saturations, and not simply the value of the saturation at the grid block centre. In this approach, for example, if a grid block has its block center slightly below the water-oil contact depth, the water saturation assigned to the block is the average over the block volume of the local saturations, and not simply the water saturation value below the water-oil contact.
The *TRANZONE option on the *WATER_GAS keyword allows the use of Gas water capillary pressure that can be entered in the water relative
permeability table (*SWT). The *TRANZONE keyword can be omitted if Pcgw is not entered.
*GASWATER and *GASWATER_WITH_CONDENSATE models must be initialized using either the *VERTICAL *BLOCK_CENTER *WATER_GAS*
or VERTICAL *DEPTH_AVE *WATER_GAS initialization option. Gas-water and gas-liquid (*GASWATER_WITH_CONDENSATE condensate option) capillary pressures are therefore only input using the *SWT table. Use of the *DWGC keyword is required with the *WATER_GAS initialization option.
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The following keywords, which must be located in the Initial Conditions section, are used with these options.
a) *REFDEPTH (reference depth)
b) *REFPRES (pressure at reference depth) c) *PB or *PBT (bubble point pressure) d) *DWOC (water-oil contact)
e) *DWGC (water-gas contact)
f) *DWOC and *DGOC (water-oil and gas-oil contacts)
g) *PDEW or *PDEWT (dew point pressure – Condensate models only
*GASWATER_WITH_CONDENSATE or *VOLATILE_OIL) Example:
*INITIAL
*VERTICAL *DEPTH_AVE *WATER_OIL
*PB *CON 2500.0 **bubble point is constant **throughout the reservoir.
*REFDEPTH 900.0
*REFPRES 3000.0
*DGOC 788.0
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