High Injection Rates Counteract Formation of Far-Reaching Fluid Migration Pathways at The Geysers Geothermal Field

Abstract

Deep underground water injections induce seismicity. When the seismic fractures coalesce into far-reaching pathways for fluid migration, the migrating fluid may reach preexisting faults and, by decreasing fault strength, can trigger major seismic events. We assume that the potential for building such pathways depends on closeness of hypocenters, similarity of fracture planes orientations, and closeness of radii taking off from the injection point, on which events locate. We define this potential as the average distance between seismic events in the space of parameters quantifying the above conditions. We show that in the studied case from The Geysers geothermal field, this potential is highly correlated with injection rate. When the overall level of injection rate is high, the higher the injection rate is, the more the potential for building far-reaching pathways for fluid migration is reduced.