Physical simulation study of fracturing monitoring of hot dry rock by borehole-surface electromagnetic method in frequency domain

Abstract The Chinese mainland has abundant hot-dry-rock (HDR) resources. However, large-scale application is significantly challenged by the fracturing and stimulation of HDR reservoirs, making monitoring HDR fracturing essential. The borehole-surface electromagnetic method, which involves borehole excitation and surface collection of electromagnetic signals, captures stronger secondary field signals, aiding in assessing and guiding the fracturing effects in HDR reservoirs. Despite its potential, research on this method for HDR fracturing monitoring is limited. To explore and validate the effectiveness and mechanism of the frequency-domain borehole-surface electromagnetic method for HDR fracturing monitoring, this study conducts physical simulation experiments. The experiments use water to simulate HDR caprock, a mixture of water and sand for the HDR layer, and a graphite-cement anomaly model for the HDR fractured zone. Results indicate significant differences in electric field response amplitudes before fracturing, during fracturing, and after fracturing. When excited below and at the center of the anomaly model, the Ey response amplitude decreases with lower model resistivity, and when excited at the center, the Ey response amplitude similarly decreases with reduced resistivity. These findings demonstrate that the borehole-surface electromagnetic method effectively reflects changes in resistivity within the fracturing anomaly model, making it a suitable electromagnetic exploration method for monitoring HDR fracturing.