A numerical compaction model of overpressuring in shales |
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| Authors: | L A Keith and J D Rimstidt |
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| Institution: | (1) Department of Geological Sciences, Virginia Polytechnic Institute and State University, 24061 Blacksburg, Virginia, USA;(2) Department of Geological Sciences, Virginia Polytechnic Institute and State University, 24061 Blacksburg, Virginia, USA;(3) Present address: U.S. Geological Survey, 86001 Flagstaff, Arizona, USA |
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| Abstract: | A one-dimensional model of sediment compaction is presented to relate pressure, porosity, permeability, and fluid and solid-particle velocities in an evolving sedimentary basin. The burial history of a sedimentary package is followed and incorporated into rate models for diagenetic reactions to predict clay compositions with depth. The governing set of nonlinear, partial differential equations constitutes a moving boundary problem and is solved by a finite difference scheme. Sedimentation rates and a permeability-porosity function for shales are required to implement the model. Additional factors are incorporated to mimic the effect of increased fluid volume generated by dehydration from clay mineral transformations and by thermal expansion. We demonstrate that the major cause of overpressuring in sediments accumulating along passive margins is nonequilibrium compaction. Sedimentation rates and strata permeability are the most important geologic factors in the formation of overpressured zones. Smectite dehydration and aquathermal pressuring play secondary roles in the development and sustenance of overpressures. |
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| Keywords: | compaction overpressuring shale permeability sedimentation rates clay diagenesis |
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