Saturated reservoir and decreasing GOR

[TBone]

A field has reached a point in depletion where it is below bubble point. The produced GOR has been reduced by about 30% and is now pretty steady. Anybody have come across similar phenomenah? To me this seems to be an effect of critical gas saturation (gas immobile) or perhaps that gas accumulates in secondary gas cap(s). When modelling this it is essential to get correct gas rel perm curves. Any tips as how to proceed with this, as imbibition experiments would be unapplicable? What is typical range of gas rel perm, f.eks with regards to corey exponent. For example could a corey exponent for gas rel perm of 3-4 be pheasable?

Hopefully somebody has experience with this, I dont know if it is a common problem.

Best Regards

[i-anuar]

probably worth checking how gas was/is measured before playing with rel perms etc :-)

[Born-Different]

Corey exponent for gas is usually in the range of 2.0-2.3. Look at your drive mechanisms: can be influence of highly dippening reservoir. As well you can this in the tight fractured formations, where migrates to the crest through the fracture network, and hardly goes to the wellbore.

[TBone]

Thats a good point about the gas, i-anuar. The oil and gas measurements have been thoroughly checked and it appears the observed effect is real.

Thanks for your reply, Born-different. Ive hade to use a corey exp of over 3 to replicate results. The strange thing is that the well is in a very updip position, so difficult to see where the gas could have migrated.

[TBone]

Thats a good point about the gas, i-anuar. The oil and gas measurements have been thoroughly checked and it appears the observed effect is real.

Thanks for your reply, Born-different. Ive hade to use a corey exp of over 3 to replicate results. The strange thing is that the well is in a very updip position, so difficult to see where the gas could have migrated.