Modeling wellbore instability in hot dry rock under various temperature conditions

Hot Dry Rock (HDR) is a renewable energy source that has garnered attention due to its abundant reserves, widespread distribution, and consistent energy supply. However, the injection of cold water during the drilling and production process of HDR can alter the temperature of the rock in the HDR reservoir, leading to variations in its physical and mechanical properties near the wellbore. These changes can impact the stability and safety of the HDR wellbore. This study investigated the alterations in the physical and mechanical properties of HDR under different temperature conditions. The results revealed that there were negligible changes in the physical and mechanical properties when the temperature rose from 25 °C to 400 °C. However, noticeable changes occurred as the temperature increased from 400 °C to 800 °C, establishing 400 °C as the threshold for physical and mechanical property variations in the granite. Building upon these experimental findings, a segmented wellbore instability model was developed and validated. The model demonstrated that an increased temperature difference between the drilling fluid and the borehole corresponded to an expanded range of borehole failure. Furthermore, higher wellbore temperatures led to more pronounced disparities between the maximum and minimum principal stress of the borehole, rendering it more susceptible to instability. The research also uncovered that the optimal drilling position was influenced by temperature.