Pore Pressure, Compaction and Tectonics

Abstract

Most physical transport and related processes depend on both, temperature and pressure. Pressure is one of the fundamental physical values. It is a scalar, which is represented with a single value in each location. The term pressure has only a real meaning for fluids and not solids. In porous media, pressure is often introduced as the pressure within the fluids in the pores, the pore pressure. The equivalent physical entity in solids is the stress tensor, which is a symmetrical 3x3 tensor with six independent values (Sec. 8.2). It can be illustrated with an ellipsoid, whose axes represent the principal stresses in size and direction. Usually, only single components or invariants of the stress tensor are important. Both, rock stress and pore pressure describe the response of the material to an external load. The “average” stress of the porous volume element is called bulk stress. It is therefore a superposition or mixture of pore pressure and rock stress and it has to be in equilibrium with all external loads.