Rock physics experiment and rock physical modeling of hot dry rock under high temperature

Currently, the investigation and monitoring of geothermal energy face significant challenges, and a lack of understanding regarding the variations in physical parameters of hot dry rock reservoirs with temperature is a crucial factor. In this study, 29 hot dry rock samples from the Gonghe Basin in Qinghai Province were subjected to high-temperature petrophysical experiments to analyze the changing patterns of physical parameters with temperature. Results show that: ①The density of rock samples gradually decreases with temperature, albeit with an attenuation range of less than 1%. ②The temperature change exerts a substantial influence on the P-wave velocity and S-wave velocity of the samples, resulting in significant attenuation between 120 ℃ and 180 ℃, with respective reductions of approximately 1 500 m/s and 800 m/s. ③A peak magnetic field intensity, seven times greater than at room temperature, is reached at 120 ℃. ④The resistivity fluctuates with increasing temperature, whose values ranges from 10 to 25 Ω·m. Based on these experimental results and with the combination of the classical Gassmann equation and fluid substitution models, this study made a quantitative analysis on the impacts of porosity and temperature variations on longitudinal wave velocity. The outcomes indicate that a porosity of 0.025 resulted in a decrease of approximately 600 m/s in the longitudinal wave velocity with increasing temperature, whereas a porosity of 0.1 caused a decrease of approximately 1 000 m/s under the same conditions.