Coupled multi-field effect on sustainable development of deep geothermal energy in cities

There is abundant geothermal resource in the intermediate-deep(200-3 000 m)and deep(>3 000 m)geothermal reservoirs in China, which has great potential for development, and the sustainable development and utilization of geothermal energy is one of the important guarantees for carbon peaking and carbon neutrality goals to be achieved on schedule. However, the exploitation process of geothermal energy involves some complex interactions between temperature, seepage and stress fields. Therefore, the achievements on the coupled multi-field effects in the development of hydrothermal geothermal resources obtained by the authors are summarized, including the resource assessment for the sustainable development of urban deep geothermal energy, the method of optimal design of exploitation schemes, and demonstrated applications in typical geothermal engineering. A multi-index assessment system for the sustainable development of urban deep geothermal energy from the aspects of temperature, water level and deformation, as well as the calculation formula of recoverable geothermal energy based on numerical model are proposed. Based on the coupled multi-field numerical model of deep geothermal well-reservoir system, the method of recoverable geothermal energy assessment which meets sustainable development criteria is presented, and the ‘traffic light system' for the risk assessment of production wells is proposed. Relying on the urban geothermal development project in the Rongdong resettlement district of Xiongan New Area, the rationality of the proposed method of geothermal energy assessment is demonstrated. Based on the coupled multi-field numerical model of deep geothermal well-reservoir system, the method of optimal design of exploitation schemes which meets the sustainable development criteria is presented, the surrogate model is constructed by the Plackett-Burman design, and the rapid optimization of parameters is realized by multiple response optimization. Relying on the urban geothermal development project in the Beijing Municipal Administrative Center, the rationality of the proposed method of optimal design of exploitation schemes is demonstrated. In this study, the theoretical and numerical supports for the sustainable development of urban deep geothermal energy are provided, which promotes the development and utilization of urban deep geothermal energy on a larger scale and with higher quality.