A sensitivity analysis of induced seismicity potential for geothermal direct heat production in faulted sedimentary aquifers: a case study in the Netherlands

Over the past decades there has been a significant increase in the direct utilization of geothermal power as a renewable energy resource. Low-enthalpy geothermal systems for direct heat production are commonly developed in sedimentary aquifers with high matrix permeability. Although such geothermal systems are not often associated with induced seismicity, the potential occurrence of induced seismic events is of concern in geothermal resource development and requires improved seismic hazard assessment associated with geothermal operations. Mechanical Analysis of Complex Reservoir for Induced Seismicity (MACRIS) is applied to evaluate the sensitivity for fault reactivation and induced seismicity potential in three-dimensional clastic reservoir models representative of low-enthalpy geothermal exploitation in the Netherlands. The reservoir models are separated by a single fault causing both no and normal reservoir offset, and, unlike previous induced seismicity studies, incorporate the effects of reservoir throw and flow compartmentalization. Results show the potential for fault reactivation and induced seismicity to be (i) substantially impacted by the three-dimensional interaction of injected cold-water volume and its destabilizing effect on complex faults in sedimentary aquifers, and (ii) characterized by moderately low seismic magnitudes for the majority of predicted events. Where reservoir throw is shown to contribute to the fault reactivation and seismicity potential, fault-related reservoir flow compartmentalization has an opposite effect and is shown to reduce the potential of a sealing or bounding fault. Results confirm the findings from previous studies by showing (i) a predominant sensitivity of induced seismicity potential to the thermo-elastic reservoir parameters and injection temperature, and the in situ stress conditions and fault frictional properties affecting slip length and resulting magnitude estimate of the seismic event. In particular, results show the seismic hazard potential to significantly decrease in the case of reservoir creep or stable in situ stress conditions, and by limiting reservoir thermal drawdown.