Something I have just noticed with Future which perhaps you could help me explain: I have been checking the forecast output for the wells in my model and something strange seems to be happening with the GOR. The reservoir solution GOR is set to 0.5 kscf/stb:

 

 

I have used the FGLR method to forecast gas production and set free gas to zero (the well produces well above the bubble point):

 

 

As such, I expect the model to forecast a GOR of 0.5 kscf/stb. However, this is not quite the case as the forecast carries a GOR of 0.492:

 

RunName

EntityName

Date

Oil Rate (stb/day)

Condensate (part of oil) Rate (stb/day)

Total Gas Rate (kscf/day)

Produced Gas Rate (kscf/day)

Solution Gas Rate (kscf/day)

Water Rate (stb/day)

GOR

Janice 2014.07.17_Forecast

P3(13)

1-Jul-2014

614.83

0.00

302.44

302.44

302.44

177.75

0.491902

Janice 2014.07.17_Forecast

P3(13)

1-Aug-2014

450.94

0.00

221.82

221.82

221.82

136.15

0.491902

Janice 2014.07.17_Forecast

P3(13)

1-Sep-2014

691.69

0.00

340.24

340.24

340.24

218.31

0.491902

Janice 2014.07.17_Forecast

P3(13)

1-Oct-2014

682.96

0.00

335.95

335.95

335.95

227.04

0.491902

Janice 2014.07.17_Forecast

P3(13)

1-Nov-2014

674.39

0.00

331.73

331.73

331.73

235.61

0.491902

Janice 2014.07.17_Forecast

P3(13)

1-Dec-2014

666.79

0.00

327.99

327.99

327.99

243.21

0.491902

 

Do you have any idea what may be causing this? It’s obviously not a large difference, but I would still like to be able to explain it. I wouldn’t rule out user error either! J If you need be to send the model across for a closer look, please just let me know.


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FUTURE solves the material balance at each time step as follows
 - Calculate current oil-in-place (OIP), GIP, WIP from STOIIP, cum prod, cum inj
- Calculate saturation pressure for this OIP, GIP (based on the assumption that saturation solution GOR is a linear function of pressure)
- Calculate reservoir pressure; if this is above saturation pressure, then solution GOR = GIP/OIP

In your situation, I suspect that the cumulative gas production is greater than original solution GOR x cum oil production. So FUTURE will be calculating a new solution GOR, based on the oil and gas volumes remaining.