A unified approach to geopressuring, low‐permeability zone formation, and secondary porosity generation in sedimentary basins

Abstract

Geopressuring, secondary porosity, and low‐permeability zones occur in many of the world's sedimentary basins and are often associated with major petroleum reservoirs. We present a mechanical model which simultaneously reproduces these phenomena. Assuming pressure solution to be the dominant rock deformation mechanism, a solid‐state rock skeleton viscosity is introduced which relates the deformation of the rock skeleton to the effective stress. Numerical solutions for compaction indicate that a soft sedimentary layer preferentially compacts to form a low‐permeability zone. There is a large liquid pressure gradient through the low‐permeability zone. In the more slowly compacting region beneath the low‐permeability zone, the pressure gradient remains hydrostatic but the absolute pressure can exceed the lithostatic pressure in the absence of hydraulic fracturing. This results in the formation of secondary porosity.