--> Abstract: Pressure and Seal Prediction and Detection in Highly Overpressured Basins to Determine Prospectivity, by Philip D. Heppard and Martin L. Albertin; #90039 (2005)

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Pressure and Seal Prediction and Detection in Highly Overpressured Basins to Determine Prospectivity

Philip D. Heppard1 and Martin L. Albertin2
1 BP Amoco, Houston, TX
2 BP America, Inc, Houston, TX

Accurate pressure prediction and seal evaluation in highly overpressured sections depends to a large degree on our concept of the relationship between pressure and fluid flow in mud rocks relative to much more permeable reservoir rocks. Decisions concerning the prospectivity of structures, or whether to continue drilling in very highly pressured mud rock, usually at considerable cost, depend on whether we can, or believe we can, identify or predict lower pressure conditions in the reservoir that would permit significant hydrocarbon columns. There are generally two schools of thought with plenty of gray between; constant flow between mud rocks and permeable rocks and therefore very similar pressure, and those that believe that there can be very different pore pressure between these rocks. The reality based on a number of cases is that while large hydrocarbon columns can be found in pressure regressions, only in some cases can these can be remotely detected from seismic velocities, predicted unequivocally by basin models, or detected while drilling. Perhaps in the majority of basins sharp pressure differences exist between mud rocks and reservoirs that are undetectable until drilled. In the Gulf of Mexico, Nile Delta, Trinidad, Caspian Sea, and the Permian Basin examples can be shown of both very sharp pressure differences that would be undetectable pre-drill or while drilling as well as pressure regressions that could be detectable by seismic velocity analysis. In any case, a clear geologic model of likely fluid flow is recommended to estimate seal potential and pore pressure.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005