[Opm] Problem with injecting field voidage replacement

[Stephen, Karl D]

Hi,
I have a problem with a simple quarter 5 spot waterflood model where I would like to inject water with field voidage replacement. There are two wells: injector, INJ, and producer, PROD. I would hope that the field voidage replacement takes the production rate in reservoir volumes and uses that to inject water at the same reservoir volumetric rate. If the injection and production volumes are the same the field average pressure, FPR, should be relatively constant.

The problem I have is that while the reported FVIR and FVPR are the same and the FWIR seems to be right as is the sum of FOPR and FWPR, the FPR (average pressure) does not remain relatively constant. Instead there is a drift as if the actual volumes injected and produced are different.

The problem seems to be to do with the definition of the formation volume factor for water, Bw, that is defined in the PVTW keyword. Bw is defined at a reference pressure which is the same as the initial average pressure. If it is 1.0 exactly then the hoped for result is obtained. If I use a more realistic value of 1.02, the volumes are incorrect and FPR eventually rises when water breaks through. Similarly if Bw is set to 0.99, the pressure goes down. I have deliberately set the compressibility of water to be very small and in PVDO, the Bo (formation volume factor for oil) is almost independent of pressure (when I started, Bo and Bw were dependent on pressure).

Perhaps I am doing something wrong with the keywords, there is a setting I need to implement or is there a a bug in the code?

Can anyone help?

I attach my code for analysis.

Using Eclipse I can get a good result. I set up the well controls with:

-  GRP  Fluid  Control   Surf     Resv   ReInj  Voidage  GRUP
--  NAME  TYPE   mode     rate     rate   frac   Frac     CNTL
--  ----  -----  ------  -------   ----   ----   ----     ----  -----
GCONINJE
    FIELD    WATER   VREP    15000     2*          1.0       NO   /
/
-- Injection control
--  Well  Fluid  Status  Control   Surf   Resv   BHP
--  NAME  TYPE            mode     rate   rate  limit
--  ----  -----  ------  -------   ----   ----  -----
WCONINJE
    INJ    WATER  OPEN       GRUP     15000        1*           8000 /
/


This doesn't work in OPM where I have to add the group control for my injector, INJ.

-  GRP  Fluid  Control   Surf     Resv   ReInj  Voidage  GRUP
--  NAME  TYPE   mode     rate     rate   frac   Frac     CNTL
--  ----  -----  ------  -------   ----   ----   ----     ----  -----
GCONINJE
    FIELD    WATER   VREP    15000     2*          1.0       NO   /
    G2       WATER   VREP    15000     2*          1.0      YES  / -- THIS IS EXTRA!!!!!!!!
/
-- Injection control
--  Well  Fluid  Status  Control   Surf   Resv   BHP
--  NAME  TYPE            mode     rate   rate  limit
--  ----  -----  ------  -------   ----   ----  -----
WCONINJE
    INJ    WATER  OPEN       GRUP     15000        1*           8000 /
/


Karl Stephen
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