HEX-M: a new tool to predict the occurrence risk of large magnitude seismic events during geothermal reservoir stimulation and operation

Abstract

We propose to predict the seismic rate and the seismic risk, assuming a linear relation between the hydraulic energy and the total seismic moment released. Two different methodologies for predicting the total seismic moment and the value of Mmax (which is the highest seismic moment released in a single seismic event occurring during or after the stimulation) are proposed. The first one assumes a linear relationship between the pumping energy and the total seismic moment produced. Thus, assuming that the pumping scheme that will be applied during the next hours or until the end of the injection is known, a prediction of the total seismic moment is possible. The total predicted seismic moment is then distributed following a Gutenberg-Richter relation, leading to an estimation of Mmax. The second method assumes that the injectivity of the well and the hydraulic diffusivity of the reservoir will remain constant during the next hours of injection or until the end of the injection. Thus, it is possible to derive an analytical pressure distribution into a given reservoir volume. The integration of the pressure over this volume is representative of the energy stored into the reservoir. Once again, assuming a linear relation between this stored energy and the total seismic moment, it is possible to derive a total final seismic moment or a Mmax value, assuming a Gutenberg-Richter distribution.