Simulating the effect of subseismic fault tails and process zones in a siliciclastic reservoir analogue: Implications for aquifer support and trap definition

Subsurface, intra-reservoir faults have subseismic portions (the fault tail) and process zones that must be considered for a complete evaluation of their role in a reservoir setting. In this paper we show that this subseismic fault domain, generally associated with all seismically mappable faults, may extend several hundred meters beyond the seismically mapped tip point, depending on vertical seismic resolution and fault displacement gradients along strike. We use reservoir modelling and fluid flow simulation of a sandstone reservoir analogue to demonstrate how a low-permeable process zone may generate steep pressure gradients in the reservoir and affect the tortuosity of reservoir fluid flow. Results and examples combined show how small adjustments in fault interpretations in the subseismic domain may significantly affect trap definition, prospect volumes, project economics and selection of exploration well locations. For production settings, we demonstrate how low-permeable fault tails and process zones may increase flow tortuosity and delay water breakthrough, thereby enhancing sweep efficiency and recovery from otherwise bypassed pockets of hydrocarbons in the reservoir. The results also indicate that process zones may contribute to pressure compartmentalization. Finally, a simple methodology for the estimation of subseismic fault continuity is presented.

► Role of the subseismic fault tip region is in sandstone reservoirs is examined.
► Process zone displacement gradients 2 orders of magnitude lower than main fault.
► Subseismic fault extensions affect trap definition and prospect volumes.
► Process zones may increase sweep efficiency and delay water breakthrough.
► Sub-seismic structural heterogeneity may therefore enhance production.