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ABSTRACT: Timing and Extent of Petroleum Formation as Determined by Rock-Eval and Hydrous-Pyrolysis Kinetic Parameters

Lewan, Michael D. U. S. Geological Survey, Denver, CO

Two types of laboratory pyrolysis used to derive kinetic parameters for petroleum formation are Rock-Eval (RE) and hydrous pyrolysis (HP). RE kinetics are determined by fitting yield curves of vaporized products swept by a carrier gas from a source rock as it is heated non-isothermally from 350° to 650°C for times varying from 12 to 60 minutes. HP kinetics are by determining rate constants for expelled oil generated from a source rock heated isothermally in the presence of liquid water at temperatures between 280° and 365°C for 12 to 144 hours. This study is the first to compare these two different kinetic derivations on the same source-rock samples bearing Type-I, -II, and -IIS kerogen. There are significant differences in the resulting kinetic parameters from these two methods. RE kinetics prescribe a broad oil window that extends over 3 km of subsurface depth. HP kinetics prescribe a narrower oil window that extends over only 1.5 km of subsurface depth. Variations in timing and extent of petroleum formation for different kerogen types are relatively minor for RE kinetics with no correlation to organic sulfur content of the kerogen. HP kinetics for different kerogen types show a greater variation in timing and extent of petroleum formation that has a general correlation with organic sulfur content of the kerogen. Applying these parameters to different geological basin histories indicates that the timing and extent of petroleum formation based on RE kinetics are overestimated for low-sulfur kerogens as observed in lacustrine source rocks (Green River Fm, Uinta basin, Utah), and underestimated for high-sulfur kerogens as observed in marine carbonate source rocks (Naokelekan/Sargelu fms., Zagros basin, Iraq).

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia