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ABSTRACT: Supercritical CO2 has excellent thermal properties and flowability, making it a potential replacement for water in efficient and eco-friendly fracturing of hot dry rock (HDR). This study develops a coupled model for fracture propagation, considering wellbore stress superposition, thermal-poroelastic effects, elastic-brittle failure criteria, and varying matrix porosity and permeability due to damage. The model's accuracy is validated through comparisons with analytical solutions and experiments. Research finds that supercritical CO2 fracturing creates more complex fractures with a wider temperature field influence. Thermal stress reduces the breakdown pressure by 55.53%, while CO2 contributes 5.89%. Breakdown pressure in HDR increases with CO2 injection rate due to pressure transmission, coupling, and filling effects. Fracture initiation and propagation can be divided into three stages: (1) Early stage dominated by thermally induced stress from; (2) Intermediate stage with competition between in-situ stresses and stress shadow effects; (3) Later stage controlled by in-situ stresses, extending along the direction of maximum principal stress. 1. INTRODUCTION Hot dry rock (HDR) refers to a type of rock formation that lacks or contains minimal stagnant water and has a high temperature (usually above 180°C). It is an important component of geothermal resources (Zhu et al., 2015). HDR contains significant geothermal energy that can be harnessed for power generation and heating, serving as a renewable and environmentally friendly energy source. In comparison to other renewable energy sources like wind and solar, HDR geothermal resources offer advantages such as stability and freedom from seasonal and diurnal limitations (Armstrong et al., 2016). Therefore, the efficient and safe development of HDR plays a crucial role in achieving sustainable energy. HDR mainly consists of metamorphic or granitic rocks characterized by dense structures and extremely low permeability, making it challenging to exploit thermal energy through natural fractures and rock matrix permeability (Olasolo et al., 2016). Hence, engineering methods are required to transform the HDR reservoir and create a complex network of fractures, providing efficient pathways for heat transfer to the working fluid.
Liu et al. (Sun,) studied this question.