Multiphysics Modeling and Microscopic Analysis of Water-Based Heat Extraction from Hot Dry Rock Reservoirs

Global geothermal exploitation has not yet adequately compensated for the shortage of fossil fuel resources, primarily owing to limited heat transfer efficiency and the adoption of inappropriate development strategies. This study develops a fluid–structure interaction model tailored to the geological characteristics of hot dry rock reservoirs to simulate the thermal exchange between reservoir rock and circulating heat transfer fluids. The heat-transfer mechanisms governing production-well performance are investigated from the complementary perspectives of molecular dynamics and fluid mechanics, focusing on the evolution of water properties and fluid–rock interactions during circulation. The results demonstrate that reservoir heat transfer efficiency is strongly influenced by fluid properties, including chemical composition and hydrogen ion content. When the fluid pH exceeds 4, a marked increase in outlet pressure and flow velocity is observed. In addition, geological parameters such as reservoir porosity and rock polarity modify outlet behavior through coupled seepage processes and interfacial molecular interactions. Higher porosity and stronger polarity promote greater seepage and mineral–fluid adsorption, which adversely affect geothermal extraction. Intermolecular attraction between the heat transfer fluid and reservoir rock is further characterized to clarify the dominant retention mechanisms, providing a reference framework for designing optimal fluid compositions for reservoirs with specific electrical conductivity requirements.