The Fault Reactivation Potential As Critical Factor in Reservoir Utilization

Reservoir utilization is frequently linked with treatments that shall enhance the reservoir productivity by hydraulic stimulation. The aim of hydraulic stimulation is to increase the formation pressure by fluid injection to create artificial fractures that act as additional fluid pathways. Large scale fluid injection used in gas and recently also on geothermal reservoirs can induce seismicity and fault reactivation depending on reservoir geomechanics and stress regime. Recent case studies in stimulation of geothermal reservoirs have shown induced seismicity as undesired side effects which need to be understood in advance of massive fluid injection. Slip tendency analysis has been successfully used to characterize fault slip likelihood and fault slip directions in any stress regime. In our study we apply the slip tendency analysis to assess the reactivation potential of shear and dilational fractures in a deep geothermal reservoir in the Northeast German Basin, based on the notion that slip on faults is controlled by the ratio of shear to normal stress acting on the plane of weakness in the in situ stress field. The results from slip tendency analysis are supported by the spatial distribution of recorded microseismicity indicating slip rather than extension along a presumed NE striking failure plane.