Effect of Reservoir Stress Path on Compressibility and Permeability of Sandstones

Abstract

Abstract Matrix permeability and pore volume compressibility are fundamentally important characteristics of hydrocarbon reservoirs because they provide measures of reservoir volume and reservoir producibility. In most laboratories these quantities are measured under hydrostatic (isotropic) loads that do not truly reflect the deviatoric stress state that exists in most reservoirs and do not adequately simulate the evolution of effective stresses in the reservoir as the reservoir is produced. Compression tests on reservoir sandstones show that both the compressibility and matrix permeability vary markedly with stress path (defined as the change in effective horizontal stress/change in effective overburden stress from initial reservoir conditions). Hence, changes in reservoir properties measured under hydrostatic loading conditions may be very misleading if applied to a reservoir that follows a non-hydrostatic stress path. Representative measurements of reservoir properties should be measured in the laboratory under loading paths that duplicate the stress path followed by the reservoir during production. Consequently, optimum reservoir management may require that the reservior stress path be determined by measuring in situ stresses early in the production history of a reservoir and periodically thereafter as the reservoir pore pressure is reduced.