Sandstone intrusions along different types of faults and their effect on fluid flow in siliciclastic reservoirs

The principle aim of this paper is to document well-preserved field examples of sandstone-filled faults in order to raise awareness of these poorly-understood structures, and discuss their potential as fault seals within injection-prone, multi-layered siliciclastic reservoirs. To achieve this goal, we have undertaken a detailed field survey in the Panoche and Tumey hills in Central California which has allowed us to recognise numerous faults filled by injected sand. In particular, sandstone-filled extensional, contractional and strike-slip faults are observed cutting the sandstone/mudstone successions. Sandstone-filled faults commonly display small offsets and apertures ranging from a few centimetres to some decimetres. Evidence of tectonic deformation is usually lacking, meaning that sand injection supported by overpressured fluids propped open the fault walls. In this paper we also describe the main mechanism leading to the emplacement of sand along a fault plane, and propose a predictive model of sandstone-filled fault distributions in different structural environments. Finally, we discuss the role of sandstone-filled faults, that although relatively small and not adding significant volume to the reservoirs, can markedly increase fluid transmissibility and thereby promote better reservoir connectivity.