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Physical and chemical aspects of the development of overpressuring in sedimentary environments
Published online by Cambridge University Press: 09 July 2018
Abstract
Fluid pressures in argillaceous sediments depend on, inter alia, mechanical stresses, temperature, diagenetic volume changes and permeability. However, the relative influence of the pressuring mechanisms depends critically upon the long time-scale compliance, C, of the overpressured layer.
In sediments undergoing first-time burial and currently exposed to their historically maximum applied stresses, C can be relatively large. Here, fluid pressure increases are principally due to mechanical causes, and overpressuring will be associated with undercompaction. The tendency for undercompaction (compaction disequilibrium) depends on the sediment thickness, burial rate and vertical permeability. In other cases, when applied stresses have been reduced by uplift, or when impermeable hard caps or seals have been formed, C may be substantially smaller. Here pore pressures may be predominantly controlled by diagenetic and aquathermal processes, with mechanical (undercompaction) phenomena being relatively less significant.
Three-dimensionally sealed overpressured zones may exhibit vertical fluid pressure discontinuities. Within a sealed aquifer, fluid pressures may rise to almost lithostatic values, relieved by episodic fracturing of the seal.
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- Copyright © The Mineralogical Society of Great Britain and Ireland 1994
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