--> Abstract: Organo-Clay Mineral Interactions: From Preservation to Oil Generation; #90063 (2007)

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Organo-Clay Mineral Interactions: From Preservation to Oil Generation

 

Bristow, Thomas F.1, Martin J. Kennedy1, Arkadiusz Derkowski1 (1) University of California, Riverside, Riverside, CA

 

In many source rocks the main phase of hydrocarbon generation coincides with illitization of smectitic clays, supporting the hypothesis that expulsion of organic compounds from interlayer sites of 2:1 clay minerals plays a role in hydrocarbon generation and cracking rather than just reactions with pore waters. In marine sediments ~90% of organic material sediments cannot be separated from the mineral phase and intercalation of organics within clay mineral interlayers leads to enhanced preservation. Sorption is reversed during diagenetic alteration of clays as expandable layers collapse (illitization) and mineral surface area is reduced, leading to expulsion of organic matter, making it more susceptible to hydrous cracking reactions. This is demonstrated by progressive steepening of TOC vs total mineral surface area trends of three source rocks with smectitic, mixed layer and illitic mineralogies. Our model reconciles organic-mineral interaction involvement in preservation and in protokerogen formation with observations of discrete kerogen particles that do not show intimate relationships with clays in rocks that have passed through the oil window. Processes leading to organic expulsion include physical collapse of interlayer sites and increased layer charge repelling non-polar sections of hydrocarbon molecules away from mineral surfaces.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California