Closing the seam - Linking seal analysis and mechanics to improve fault stability prediction

The reactivation of critically stressed faults during production-induced pressure changes bears a big risk and limits the total recoverable volume as for safety reasons pressure changes must be kept lower than potentially possible. Reservoir pressure and regional stresses can be reasonably well measured and estimated before the start of production. However, to maximize recovery while minimizing the risk of fault reactivation, assessing fault strength as accurately as possible is crucial. The strength of a fault depends on the mechanical properties of the fault rock (friction angle, cohesion), which can vary strongly over short distances, depending on displacement, complexity of fault geometries and available host rock lithologies. Especially clay minerals entrained in the fault core can tremendously reduce the strength of faults. We develop a workflow that uses standard fault seal algorithms (e.g. Shale Gouge Ratio) to estimate shale content in the fault rock and subsequently provide corresponding frictional properties for each fault cell in a reservoir model. This will be a function of the statistical distribution of shale smears in a fault depending on mechanical properties at time of faulting, as well as present day effective stress.