Gas generation -- A major cause of deep Gulf Coast overpressures

Abstract

Compaction is generally regarded as a principal cause of overpressuring and hydrocarbon expulsion in sedimentary basins. However, recently available shale porosity data on individual Gulf Coast wells suggest that in many cases compaction plays no role in either of these processes. The evidence for this is that shale porosity is either constant or increasing at the depths where overpressures occur and where hydrocarbons are being generated. In the absence of a decrease in porosity with sediment load (depth), gas generation becomes the principal cause of overpressuring and hydrocarbon migration. This can have important implications in modeling overpressures in the Gulf Coast. The purpose of this article is to show some of the evidence that compaction is not occurring in the deeper (> 10,000 ft) sections of these wells and that gas generation is the major cause of overpressures at depths where compaction no longer occurs.