Petroleum Migration and Reservoir Filling

ENGLAND, WILLIAM A., BP Research, Sunbury-on-Thames, U.K.

The organic constituents of petroleum reservoirs frequently show measurable compositional variations both laterally (between wells) and vertically (within a single well). The pattern of variation is controlled by the geological setting of the reservoir, which influences the way in which migrating petroleum fills the reservoir from one or more source kitchens. Having achieved a high petroleum pore saturation, the reservoir fluids may then redistribute themselves at rates that are often comparable to geological time periods. Mass transfer by diffusion and density-driven convection must be considered, and their time scales compared with the elapsed time since the accumulation was filled. In many cases, the compositional variations inherited from the filling process persist to the present day.

Post-emplacement processes that may affect the petroleum composition include the effects of gravitational and thermal gradients, deasphaltening, and phase changes. Water washing and biodegradation may also be significant, providing that certain conditions are met.

This talk outlines the mechanisms by which reservoirs fill and mix, and describes how this can lead to observable lateral differences in composition. The goal is to improve the characterization of petroleum reservoirs by combining geochemical and engineering data into a scientifically consistent framework.

The talk concludes with a discussion on important unsolved problems in petroleum migration/reservoir filling. It is suggested that future major advances will rely on at least some of these problems being solved.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)