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Hi,

I'm having trouble with understanding my volume calculations in Petrel. I have had to remodel my OWC as a new appraisal well has resulted in an OWC that was lower than anticipated. One of my hypotheses is that the OWC is somewhat subhorizontal, possible due to hydrostatic conditions not being met. I want to calculate volumes that incorporate some kind of water flow through the reservoir bending the OWC, prior to assessing potential compartmentalization (which is strange because salinity below the OWC is absolutely the same).

Now I've modeled a surface using welltops at the OWC in all wells and this seems to work well. This has, however increased the potential volume so greatly that I want to know how Petrel calculates this exactly, just to strengthen my reporting. How does Petrel handle sub-horizontal/bent OWCs? Whithin each gridcell does the curvature of the OWC have any affect on the volume calculation? The curvature of the OWC is quite a lot in comparison to the gridcell size (100m; and OWC lateral change is 12ft over approx 600m).

Please advice me in this issue!

Thanks

I think the uncertainty does not arise from the way petrel handles volume calculations from a curved OWC. Petrel was made for this and maybe only Eclips can do it slightly more accurate. Petrel knows the cell corner geometry and uses subfractionation of volumes to get close to EXACT calculations. The onyl thing you should worry about is your gridding of your OWC surface. You can make this 1 m, and then every square m will be calculated separately and this will be very accurate...
BUT, is this accuracy needed and does it add value, as I assume you don't know what you contact does between well locations. It all depends on you uncertainty levels and modeling OWC in hydrodynamic reservoirs is very difficult. Furthermore I find the 12ft difference over 600m quite high (for some sort of hydrodynamic push) and, as you mention, compartmentalization may be a better solution to you 'problem'. Remember, interpreting salinity differences is sort of a biased method as a different salinity over short distances gives very high chance to fluid flow baffles, while a similar salinities does not directly indicate connectivity. Water with the same salinity may have been present before compartmentalization occurred. Also it may be possible for water to flow through a structure or lithology that hampers flow for oil.

just my 50 cents, and of course I don't know the full 'situation' in your reservoir.

Maybe you can enlighten us with answers to the following questions?
Is compartmentalization not likely due to other data? Is there reason to think hydrostatic conditions are not likley to be present?