The effects of fault damage zones on geothermal activity in siliciclastic reservoirs: A modelling study.

ABSTRACT: We have studied the impact of considering permeability-reducing damage zones in thermo-hydro-mechanical (THM) simulations of geothermal cold water injection in siliciclastic reservoirs. The impact was assessed by analysing pressure- and temperature distributions from a FLAC3D-ToughREACT, and seismicity metrics obtained from a seismicity simulator that incorporates fault roughness. The model geometry and input parameters are based on a representative fault zone in the West Netherlands Basin, obtained via geological interpretation of seismic data and well logs. Two scenarios are presented: one without and one with damage zone. Our results show that the damage zone causes compartmentalization of pressure, and directs the cooling front away from the main fault. The damage zone shelters the main fault from stress changes, resulting in fewer seismic events and a lower maximum observed magnitude than without damage zone. We note that seismicity was analysed on the main fault only; seismicity on secondary faults in the damage zone have not been considered. The trends identified in this study suggest that damage zones should be considered in THM simulations.