Cascade and effective utilization of medium and deep geothermal energy: A comprehensive review and application prospects

Abstract

Geothermal energy has great potential in the green transformation of energy. The utilization of medium and deep geothermal energy should be considered from the comprehensive perspectives of underground and aboveground systems, energy cascade utilization, and tailored solutions. Currently, there is a lack of reviews covering these aspects. This paper comprehensively reviews the cascade development and effective utilization technology of medium and deep geothermal energy, focusing on the research progress of underground extraction and aboveground utilization systems. The underground technology includes U-shaped well, downhole coaxial heat exchanger and super-long gravity heat pipe, and the heat extraction efficiency is optimized by closed-loop design. The aboveground system combines power generation (such as organic Rankine cycle), heating and multi-stage co-production modes, and integrates solar energy, heat pump and phase change heat storage technologies to improve energy efficiency. Technical and economic optimization and system integration are the key to large-scale application. Taking Xiong'an New Area in China as an example, the differential development strategy of multi-temperature geothermal reservoirs and the cascade mode are discussed. The Xiong'an demonstration case verifies the feasibility and low-carbon potential of cascade utilization, and the suggestions provide a reference for similar geothermal areas in the world.