--> Pressure Seals--Hydrocarbon Plugging Hypothesis: Is Enough Gas Available in Natural Systems?, by J. Whelan, J. Seewald, and L. Eglinton; #90986 (1994).

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Abstract: Pressure Seals--Hydrocarbon Plugging Hypothesis: Is Enough Gas Available in Natural Systems?

Jean Whelan, Jeffrey Seewald, Lorraine Eglinton

Previous observations on characteristics of organic matter across pressure transition zones from this laboratory led to a "hydrocarbon plugging hypothesis" for pressure seal formation and maintenance: oil and heavy bitumen can dissolve in methane and move upward as a single phase at the high pressures typical of zones beneath pressure transition zones. Pressure build-up beneath the seal, possibly via oil cracking and gas generation, and seal rupture were proposed to allow episodic streaming of this solution through the pressure drop of the pressure transition zone. The resulting pressure drop was calculated to cause formation of a separate gas phase accompanied by precipitation of heavy oil and asphalts, both of which would contribute to replugging of the seal. Here, we describe field data from the Gulf Coast, Nova Scotia Venture Field, and the Mahakam Delta which suggest that this mechanism of seal formation and rupture may be wide spread. Comparisons are made to laboratory data delineating amounts of gas available from different total organic carbon amounts, kerogen types, and sediment types. We also discuss which systems could generate sufficient gas to drive this process.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994