--> ABSTRACT: The Physics of Petroleum Expulsion/Source Rock Compaction: Solution to an Old Controversy in Petroleum Geology, by J. K. Michelsen, G. K. Khorasani, and J. Diaz; #91021 (2010)

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The Physics of Petroleum Expulsion/Source Rock Compaction: Solution to an Old Controversy in Petroleum Geology 

MICHELSEN, JOHAN K., GANJAVAR KHAVARI KHORASANI,  and JULIO DIAZ

Petroleum expulsion and related overpressure in surrounding sediments occur, due to mechanical instability of the source rock matrix, when a significant volume fraction of the rock matrix, i.e., kerogen is transformed into a low viscosity petroleum fluid (typically >1-10 percent by volume of the rock). The expulsion is driven by gravity (density contrast between the rock matrix and the free petroleum) and the fluid potential gradients between the free petroleum in the source rock and fluids in surrounding sediments. The rock matrix behaves as a viscous fluid, of which bulk and shear viscosities depend on maturity and the self-generated petroleum porosity. The matrix compacts at a rate depending on the rate of petroleum desorption from kerogen, the viscosities of the rock matrix, the viscous forces between the rock matrix and petroleum fluid, and the capillary properties and fluid pressure of the water wet sediments surrounding the source rock. The physical model presented reproduces observed features of real source rocks, and we will demonstrate how spatial variation in kerogen quality and quantity controls the dynamic behavior of the system, including porosity/pressure shock-wave generation/propagation. Petroleum dikes and sills are explained as instabilities, originating from the intersection between porosity waves and heterogeneities in rock properties. Most processes previously suggested as responsible for expulsion, are shown to be of subordinate nature. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.