A generic framework for overpressure generation in sedimentary sequences under thermal perturbations

Abstract

Abstract Abnormal pore pressures in excess of the hydrostatic equilibrium are observed in natural and artificial sediment systems worldwide. Such overpressure exerts a fundamental control over the diagenesis, stability, and productivity of both sedimentary reservoirs. The basin dynamics for overpressure generation involve complex THMC processes during sediment accumulation. In this paper, we develop a generic framework for thermo-chemical consolidation in natural and artificial sedimentary sequences by extending Biot’s classical poroelasticity. The proposed theoretical model is then conveniently recast into an explicit form for one-dimensional sedimentation. The resulting formulation essentially extends the original Gibson’s theory by incorporating coupled THMC effects in general sedimentary sequences, and a hierarchical scrutiny of different overpressuring mechanisms thus becomes straightforward. Moreover, a closed-form equation is derived from the new chemo-thermo-poroelasticity model for accreting sediments, and the critical temperature for pore pressure changes via hydration/dehydration is thus determined. The model demonstrates that overpressuring and depressuring are not mutually exclusive because of the competition between water volume changes and thermal strains induced by chemical reactions. By using evolutive properties of a reactive artificial sediment, our model calculations have highlighted the critical influences of the sediment and environment temperatures and deposition rate on the contribution of each overpressuring mechanism.