Evaluation of fluid flow in enhanced geothermal reservoirs based on induced microseismic multiplets

The relationship between induced microseismic multiplets and fluid injection during hydraulic stimulation of geothermal reservoirs is a possible technique for monitoring fluid flow in fractures and identifying major fluid flow paths in reservoirs. We have identified induced microseismic multiplets in a reservoir zone where preexisting fractures were enhanced by fluid injection to be major fluid flow paths. Analysis of the time intervals of microseismic events shows that the occurrence of multiplet events is quasi-periodic rather than random and is inferred to be related to fluid flow rate in fractures. Our analysis shows that the energy of multiplet events per unit volume of injected fluid and time tends to be larger at the fractures near the outlet zone, where fluid flow rates in fracture are expected to be higher. We derived and evaluated a parameter comprising the event energy, injection fluid volume, and timing of multiplet occurrence that shows promise as an indication of fluid flow rate in fractures.