New insights on the Green River petroleum system in the Uinta basin from hydrous pyrolysis experiments

The Tertiary Green River petroleum system in the Uinta basin generated abou t 500 million bbl of recoverable, high pour-point, paraffinic crude oil fro m lacustrine source rocks. A prolific complex of marginal and open-lacustri ne source rocks, dominated by carbonate oil shales containing up to 60 wt. % type I kerogen, occur within distinct stratigraphic units in the basin. P etroleum generation is interpreted to originate from source pods in the bas al Green River Formation buried to depths greater than 3000 m along the ste eply dipping northern margin of the basin. Producing fields in the Altamont -Bluebell trend have elevated pore-fluid pressures approaching 80% of litho static pressure and are completed in strata where open fractures provide pe rmeability. Active hydrocarbon generation is one explanation for the origin of the overpressured reservoirs. In this study, experiments were undertaken to examine the mechanisms of hyd rocarbon generation and accumulation in the Uinta basin. We combined analys es of representative source rocks from the entire Green River stratigraphic section with detailed laboratory simulation experiments using both open- a nd closed-system pyrolysis. This information provides new insights on lacus trine source rock lithofacies, gas-oil-source rock correlations, hydrocarbo n generation kinetics, and basin modeling. The results show that the basal Green River Formation contains a unique type I source facies responsible fo r generation of paraffinic crude oils. The classic type I oil shales in the upper Green River Formation correlate well with low-maturity aromatic-asph altic samples. We determined kinetic parameters for the source rocks and us ed them to develop basin models for hydrocarbon generation. The models show that hydrous pyrolysis kinetic parameters are more consistent with the nat ural data in terms of predicted timing and extent of oil generation as comp ared to models using Rock-Eval kinetics.