Evaluation of the Modification Potential for Carbonate Geothermal Rocks by considering Multiple Mechanics Properties and Acid Dissolution in the Jizhong Depression, China

Abstract

Abstract Evaluation of geothermal reservoir modification potential is of great significance for improving the efficiency of geothermal exploitation and reducing costs. However, it is difficult to accurately evaluate the potential of geothermal reservoir modification given the limited number of parameters used in practical studies. Therefore, an evaluation method that considers the potential of geothermal development by applying multiple parameters is essential. In this study, five types of rock samples are collected in the field from the Fujunshan Formation, Gaoyuzhuang Formation, Majiagou Formation, and the second and fourth groups of the Wumishan Formation. The uniaxial compressive strength (UCS) and uniaxial tensile strength (UTS) of rock samples were obtained by uniaxial compression tests and Brazilian splitting tests, followed by the calculation of the brittleness index utilizing UCS and UTS. Then, the joint roughness coefficient and crack width were obtained by 3D scanning and postprocessing. In addition, the fracture extension degree of each lithology was obtained via acid dissolution experiments. Analytical hierarchy processes (AHP) associated with expert experience were adopted to evaluate the modification potential of rock samples under hydraulic stimulation and acid etching based on the above parameters. The results show that the carbonate rocks of the Majiagou Formation are prone to cracking, efficient for flow and heat exchange, sensitive to acid dissolution, and thus have the highest potential for modification. The proposed evaluation method and implemented case study can provide a practical reference and solid base for further applications.