Investigating fault slip in a model of an underground gas storage facility

Abstract Several underground gas storage facilities are being created in the Netherlands. Due to their location in areas where small earthquakes are frequently induced by hydrocarbon recovery, an investigation is carried out into the relationship between pore pressure variations and fault slip. It uses a specially created geomechanical model of a generic reservoir which is subjected to depletion and storage simulations. The tilted reservoir is divided by three normal faults and covered by a thick salt layer, where the stresses acting on the model are assumed to be induced by gravity only. The results from this numerical modelling are that fault slip occurs locally during depletion, due to compaction of the reservoir, and that no significant amounts of additional slip occur when the reservoir is subjected to alternating injection/ extraction periods. The scope of this paper is limited to investigating fault slip in or near the reservoir, when the pressure is kept below the initial pore pressure. The influence of high well rates and the effect of time-dependent relaxation of built-up stresses on the occurrence of microseismic events have not been assessed in the model.