Experimental research on deformation response of hot dry rock (HDR) geothermal reservoir during hydraulic modification at 300 °C and depth 2500 m

In the stages of reservoir construction and geothermal exploitation, the rock deformation is an important factor in the study of the reservoir stability. However, the existing laboratory research in this area pay far less attention to the macroscopic deformation of the reservoir rock mass. Hydraulic fracturing experiments have here been conducted at a temperature of 300 °C, an axial pressure of 65 MPa, and a confining pressure of 60 MPa. The quantitative relationship between the granite strain (axial, radial, and volumetric) and the water injection pressure during hydraulic fracturing has then for the first time been determined experimentally. Meanwhile, the deformation response of granite geothermal reservoir during hydraulic modification has also been discussed. As a result, the maximum opening of the hydraulic fractures was in the range of 10−1 μm - 10−2 μm and the maximum volumetric strain rate of the rock mass was 1.71 × 10−4 s−1. Microseismic events preferably occurred during periods of high volumetric strain rates when the injection pressure fluctuated repeatedly. During geothermal exploitation, the structural changes caused by hydraulic fractures and thermal cracks resulted in greater potential for contraction of the rock mass. These research results provide a reference for geothermal reservoir reconstruction and stability assessment. •The quantitative relationship between granite strain and injection pressure is shown in the high-temperature hydraulic.•A maximum hydraulic fracture opening range of 10−1 μm - 10−2 μm is obtained by a hydraulic experiment at 300 °C.•The reservoir high strain rate induced by water injection is an important factor leading to microseismie events.•The structural changes induced by hydraulic fracture and thermal cracks result in greater deformation of the reservoir.