Tim E. Ruble¹, Michael D. Lewan², R. Paul Philp³, Christopher J. Boreham⁴

(1) CSIRO Petroleum, North Ryde, Australia
(2) U. S. Geological Survey, Denver, CO
(3) University of Oklahoma, Norman, OK
(4) Australian geological Survey Organisation, Canberra, Australia

ABSTRACT: Modeling oil generation in the Green River Petroleum System, Uinta Basin: Significance of appropriate experimental kinetic parameters

The Green River petroleum system in the Uinta Basin is responsible for almost 500 million barrels of paraffinic crude oil and is a classic example of hydrocarbon generation from lacustrine source rocks. Producing fields have elevated pore-fluid pressures which approach 80% of lithostatic pressure. The reservoirs have no cap rock or conventional trapping mechanism and result from permeability formed via high pore pressure fractures. One explanation for the origin of these overpressured reservoirs is active oil generation. In this study, input parameters from published geologic models of the Uinta Basin were used to evaluate the effects of various experimentally derived kinetic parameters on the location, rates and timing of oil generation.

Basin models using Rock-Eval and MSSV derived kinetic parameters have encountered difficulties in that hydrocarbon generation occurs too early and too quickly to account for the present overpressured reservoirs. There is a large pulse of generation during rapid burial 20-30 Ma, followed by a decline from 20 Ma to present, during which time the overpressure dissipates. As a result, the geothermal gradient, eroded section or permeability input parameters in these models must be lower than measured data to sustain overpressure. However, kinetic parameters determined by hydrous pyrolysis experiments are more consistent with natural data and predict active oil generation as a viable mechanism for the origin of overpressured reservoirs. This study illustrates the need to use appropriate kinetic parameters for proper evaluation of petroleum generation and its consequences on developing a quantitative understanding of basin evolution.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado