Post-Seismic Variation in Petrophysical Parameters and Heat Storage at the Tuzla Geothermal Field, Biga Peninsula (NW Anatolia) From Resistivity-Depth Model Using Differential Evolution Algorithm

Electrical resistivity has been shown to offer significant insights into post-seismic changes in geothermal reservoirs; however, its interpretation is complicated by the fact that it is controlled not only by temperature, but also by porosity and clay content. In this study, we used a post-seismic electrical resistivity-depth model from magnetotelluric data to estimate the temperature changes following a seismic swarm in the vicinity of the Tuzla Geothermal Field in the Biga Peninsula of northwestern Anatolia. In the absence of pre-seismic resistivity data for the field, we attribute the characteristic part of the post-seismic model to the seismic swarm. Temperature changes were then evaluated using pre- and post-seismic wellhead temperature observations together with the post-seismic resistivity-depth model. In order to address the relationships between resistivity and petrophysical parameters, the present study combined the established equations for temperature, porosity and clay-related effects. The estimation of petrophysical parameters from combined equations was then conducted using the differential evolution algorithm (DEA), a method that has gained popularity due to its effectiveness in solving non-linear optimization problems. The main contribution of this study lies in the integrated use of a unified petrophysical framework and the DEA to jointly estimate post-seismic changes in temperature, porosity and clay content from the resistivity model. Furthermore, an estimation was made of the reduction in stored heat within the defined reservoir zone. The results indicate that the observed increase in resistivity is primarily associated with a decrease in reservoir temperature, which is consistent with the observed decrease in wellhead temperatures. In addition, changes in clay content and porosity contribute significantly to the resistivity response. The findings demonstrate the efficacy of models of resistivity-depth, obtained following seismic activities, in facilitating the inference of changes in petrophysical parameters and thermal state in geothermal systems.