ANALYSIS OF PORE-FLUID PRESSURE-GRADIENT AND EFFECTIVE VERTICAL-STRESS GRADIENT DISTRIBUTION IN LAYERED HYDRODYNAMIC SYSTEMS

A theoretical analysis is carried out to investigate the pore-fluid pr essure gradient and effective vertical-stress gradient distribution in fluid saturated porous rock masses in layered hydrodynamic systems. T hree important concepts, namely the critical porosity of a porous medi um, the intrinsic Fore-fluid pressure and the intrinsic effective vert ical stress of the solid matrix, are presented and discussed. Using so me basic scientific principles, we derive analytical solutions and exp lore the conditions under which either the intrinsic pore-fluid pressu re gradient or the intrinsic effective vertical-stress gradient can be maintained at the value of the lithostatic pressure gradient. Even th ough the intrinsic pore-fluid pressure gradient can be maintained at t he value of the lithostatic pressure gradient in a single layer, it is impossible to maintain it at this value in all layers in a layered hy drodynamic system, unless all layers have the same permeability and po rosity simultaneously. However, the intrinsic effective vertical-stres s gradient of the solid matrix can be maintained at a value close to t he lithostatic pressure gradient in all layers in any layered hydrodyn amic system within the scope of this study.