Static pressure gradient in gas-condensate well

[kochichiro]

Hello guys, my group tested two wells on carbonate reef gas-condensate reservoir and I’ve encountered a problem. In one of the wells static pressure gradient decreasing with depth, in other static pressure gradient increasing with depth. It is not related to liquid loading because in both cases pressure gradient exhibits linear trend.
The only one solution that I can think of is that one well located on top of the gas cap (one with decreasing pressure gradient) and other on the wing of the structure close to the gas-oil contact (one with increasing pressure gradient).
Maybe someone have similar experience? Is there any other explanation of such phenomena?

[Shakespear]

Throw in a picture of what you are looking at. Mask depths first digit in your graph if you are worried about the data being proprietary .

Look here also

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You are a Lucky Boy today. I started to dig more along this line and found this.

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Doing searches on this website may find EVERYONE something interesting :-)

Enjoy

[kochichiro]

Here is the picture

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[vinomarky]

Are both these well measurements prior to production? - If not, and if you have some pervasive perm heterogeneity (ie higher perm lower on structure) depletion could be affecting it.

Are they both from the same period? - If not, could offset production be depleting the field through a common aquifer? (I've seen this before)

Are those depths TVD? It's odd that they don't start, end, or at least extrapolate to a common pressure..... their pressures cross over mid column. If they are TVD, then either you've had some sort of differential depletion, you've got some error in your measurements, or they are different pools (or if connected, via a different density fluid)

[kochichiro]

The wells are in production for two years. Both wells belong to Upper Devonian age. Reservoir rocks are carbonate reef sediments.
You are right about permeability heterogeneity. I am observing it from well tests. Well # 26 has 1010 md permeability and Well # 22 has 75 md permeability. I think that Well # 26 probably belongs to foreslope, it was confirmed GOC below perforation interval for this well also. For Well # 22 GOC in vertical direction is absent.
Both depths are TVD. I agree with you that wells probably belong to different reservoirs. Geoscientists from other service company said that there is some dislocation between this wells. But geologists and reservoir engineers from reservoir engineering department of our company draw uniform model with absence of GOC.
So, that is why I asked about to what this phenomena can be related. I just wanted to confirm my suspects.

[vinomarky]

If you indeed trust your measurements, and they are undisturbed pressures, then (in my humble opinion) they are from different compartments

If they had different gradients, that extrapolated back to some shared pressure value (GOC/GWC etc) then they could conceivably be connected hydraulically (ie via a water leg), but different properties. The more I think about it, the fact that the pressures cross over mid column makes me increasingly believe that the highest likelihood is that they are from different (unconnected) pools.

[Shakespear]

If you indeed trust your measurements, and they are undisturbed pressures, then (in my humble opinion) they are from different compartments

Yes, sounds reasonable.

Take a look at this

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Check out discussion on page ~56,
The practice of reservoir engineering
Autorzy L. P. Dake

A Method For Validating The Volume Of Drainage Cells In Oil Fields
Mike Shepherd - Shell

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[link Point to another website Only the registered members can access] However in this presentation some images I think are missing :-(

How to find them these cells

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Genesis field, Gulf of Mexico: Recognizing reservoir compartments on geologic and production time scales in deep-water reservoirs

[kochichiro]

Thank you very much Shakespear. You provided me with valuable material.

[darcyoil]

Decreasing pressure gradient? Maybe there is an integrity issue here. Did you check the temperature gradient? Any reversal?

[kochichiro]

Hello. I have updated “Static pressure gradient in gas-condensate wells” file with temperature gradient -

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[darcyoil]

Kochichiro: No, I meant the gradient downhole. A surface reversal is not the problem here i think. Plot your temperature versus depth and see if the curve bends back (reverses). If it does, then maybe what you're recording is a "flowing" static gradient due to lack of integrity