Modeling consolidation and fluid flow in sedimentary basins

Abstract

Topographic elevation and sediment consolidation are principal components that determine pressure distribution and flow of fluids in a sedimentary basin. Although fluid flow as a result of topographic elevation can be easily simulated, porewater movement as a result of consolidation of sediment requires a physically more complex approach, as it involves sediment deformation, moving boundaries and changing sediment properties. This paper describes a mathematical model based on Terzaghi's theory of the consolidation process that calculates fluid flow as a result of consolidation, and additionally incorporates fluid flow from topographic elevation. Porosity changes are calculated as a function of fluid pressure changes, using the equation of state for porosity, thereby avoiding empirical porosity/depth formulations such as Athy's equation. It is assumed that hydraulic conductivity and sediment compressibility are reduced during consolidation, and hydraulic diffusivity remains approximately constant during the consolidation process. The permeability/porosity relation is described by the Kozeny-Carman function. The capabilities of the program are illustrated by two simple experiments.