Physical character and fluid-flow properties of sandstone-derived fault zones

Abstract: Evaluation of hydrocarbon entrapment and production patterns in faulted sandstone r servoirs requires understanding of the nature and fluid-flow properties of sand-stone-derived fault zones. This study documents the interrelationships between sandstone composition, deformation mechanisms, fault-zone character, and fluid-flow properties (permeability and capillary properties) using a global sandstone dataset. Quartz-rich sandstones deform by cataclasis (most commonly), diffusive mass transfer, or a combination of these processes to form deformation bands. The fluid-flow properties of these zones depend on deformation mechanism(s). Faulting of mineralogically immature sandstones results in the formation of clay-matrix gouge zones by a combination of processes, including cataclasis, intergranular sliding in clay-rich materials, and diffusive mass transfer. Clay-matrix gouge zones generally have lower permeabilities and higher capillary displacement pressures than deformation bands. Most deformation bands have capillary properties ufficient o maintain hydrocarbon column-height differences of less than 75 m across them, whereas clay-matrix gouge zones can potentially seal hydrocarbon columns with heights of several hundred metres. Bot