Analysis of the Correlation Between Post‐Injection Wellhead Pressure Decay and Trailing Seismicity

Abstract

Abstract Fluid injection during reservoir stimulation aims to enhance reservoir permeability but induces seismic activity that persists for hours to months after injection has stopped. In this study, we investigate the correlation between the post‐injection wellhead pressure decay and the decrease in seismicity rate using data from multiple Enhanced Geothermal Systems injection operations characterized by an abrupt shut‐in. We evaluated several statistical models to represent the seismicity rate and the pressure decay. Using the best fitting model, we show that the time required to reach a given fraction of the initial seismicity rate and of the initial pressure are correlated, with the pressure relaxation being longer than the seismicity rate relaxation. No correlation is observed between seismicity decay and injection parameters such as injection volume, average injection pressure, or injection duration. These observations suggest that the relaxation of the pore pressure drives the decrease in seismicity, which has strong implications for reservoir management.