High-Resolution Analysis of Microseismicity Related to Hydraulic Stimulation in the Berlin Geothermal Field, El Salvador

Abstract

We investigate microseismicity during a hydraulic stimulation at the Berlin Geothermal Field, El Salvador. The site was monitored using 13 3-component seismic stations deployed in shallow boreholes. Three stimulations were performed in the well TR8A with a maximum injection rate and well head pressure of 140l/s and 130bar, respectively. The catalog of 581 seismic events were relocated using the double-difference relocation algorithm based on cross-correlation derived differential arrival time data. We also recalculated source parameters using the the spectral ratio method. We investigated the source parameters and spatial and temporal changes of the seismic activity based on the refined dataset and studied the correlation between seismic activity and production. The achieved hypocentral precision allowed resolving the spatiotemporal changes in seismic activity down to a scale of a few meters. We observe clustering of the seismicity around the injection well as well as the migration of seismicity outside of injection point along the pre-existing faults. The migration of seismicity is determined by increasing injection rate (Kaiser effect). We observe larger magnitude events after the shut in of the injection well. We finally observe the decrease of the static stress drop with the distance from injection point.