Volumetrics of Petroleum Generation: Implications for Expulsion and Overpressure.

In this study, the author explores the volumetrics of petroleum generation using a well constrained set of source rock and Kimmeridge Clay Formation petroleum samples at maturities covering the complete generation window from the North Sea. Densities of pure kerogen isolates were determined using density gradient centrifugation. Best estimates were derived for the composition of petroleum as a function of maturity. The PVTX properties of the petroleum were derived using PVTSim v.10. Combining the kerogen density data with the petroleum PVTX data, and placing these data into an algebraic mass balance scheme, the volume and pressure changes attendant upon petroleum generation were determined as a function of maturity. For source rock temperatures up to ∼130°C, the volume expansion is about 21% of the immature kerogen volume with an attendant pressure increase of about 10 MPa within the uncertainty of the methods in a closed system. Significant increases in volume, up to 71% with a concomitant pressure increase of about 33 MPa only occur at temperatures >130°C, when generated fluids have high gas-oil ratio. The results suggest that a completely closed source rock system can become overpressured during the main phase of oil generation. [ABSTRACT FROM AUTHOR]