Review on heat extraction systems of hot dry rock: Classifications, benefits, limitations, research status and future prospects

Hot dry rock geothermal resources are widely distributed at various reservoir depths, possessing high energy potential and substantial extraction prospects. Heat extraction systems of hot dry rock aim to unlock the vast subsurface geothermal energy, offering a sustainable solution for the renewable energy. This review offers a comprehensive overview for heat extraction systems of hot dry rock, including Enhanced Geothermal Systems, Closed-Loop Geothermal Systems, and Open-Loop Geothermal Systems. Here, we elucidate the stimulation mechanism for increasing the permeability of hot dry rock. Subsequently, it delves into the heat extraction principles and the current research status of the diverse heat extraction methods. Additionally, the review assesses the advantages and the disadvantages associated with the different geothermal systems and the working fluids. Finally, the feasibility and economy of each system are evaluated respectively, and their prospects are proposed. This review holds great significance for the research and commercial applications of the hot dry rock heat extraction technologies.