Analysis of Spatial-Temporal Variation of B-value in San Emidio Geothermal Field

Abstract

Induced seismicity can occur in geothermal fields, where production and injection processes cause changes in pore pressure and effective stress that trigger seismicity. A total of 1,761 seismic events occurred over a 31 days period, with 1,575 events occurring during the shut-in phase due to a rapid increase in pore pressure and a decrease in effective stress in the production well zone and fault zone. The majority of events were found in the fault zone, which used as a fluid migration pathway. This study aims to analyze seismicity parameters, specifically the b-value, spatially and temporally using the Gutenberg-Richter Relation and Maximum Likelihood methods to understand the rock stress conditions caused by changes in pore pressure during the shut-in phase. In general, the b-value obtained at the San emidio geothermal field is relatively low at 0.68. The spatial variation of the b-value obtained ranges from 0.6 to 1.1. High b-values are found in the production zone experiencing increased pore pressure during the shut-in phase, while low b-values are found in the fault zone, which tends to accumulate high stress. Temporal variations in b-values show a de-crease in b-values during shut-in and the occurrence of events with high magnitudes relative to the catalog.