# Simulation of Gas Fracturing in Reservoirs Based on a Coupled Thermo-Hydro-Mechanical-Damage Model
###### Abstract
Moreover, the injection of fluids has the potential to generate microfractures within the rock formation, thereby rendering them more susceptible to inter-slip and effectively \"lubricating\" their mobility [9]. Furthermore, when faults are subjected to excessive pressure, it can easily trigger seismic events. Additionally, the occurrence of water blockage hampers the desorption rate of gas in the reservoir matrix, resulting in decreased extraction efficiency [10]. The implementation of hydraulic measures frequently leads to water infiltration in the coal mass, which can be difficult to eliminate and gives rise to a \"water blockage\" effect that considerably reduces the permeability of the coal seam. Lastly, hydraulic fracturing encounters difficulties in water-scarce regions. The major shale gas reservoirs in China are predominantly located in arid and semi-arid regions, posing significant limitations on the extensive industrial development of coabled methane. Consequently, waterless fracturing technologies have emerged as a focal point, with gas fracturing technology attracting widespread attention as an environmentally friendly, waterless fracturing technique. The enhancement of permeability through gas fracturing involves two primary methods. The first method utilizes liquefied carbon dioxide or liquid nitrogen, which, when heated, undergoes a phase change and expansion, leading to high-pressure gas fracturing that increases permeability. The second method involves the use of a pressure device to directly generate high-pressure gas for fracturing and permeability enhancement. It can be combined with various approaches to create fractures in the reservoir. One example of a technique to increase the flow capacity of the mining area and adjacent strata and facilitate the extraction of coalbed methane is through the application of high-temperature gas, high-pressure gas, or periodic gas impacts [11; 12]. The use of gas fracturing can circumvent the detrimental impacts resulting from water presence. Throughout the process of fracturing, the gas has the ability to transition into the gaseous phase, thereby mitigating the effects of capillary pressure. In their research, [PERSON] et al. [13; 14] employed nuclear magnetic resonance, acoustic emission (AE), and uniaxial compression tests, and demonstrated that gas fracturing has the potential to stimulate the expansion of micropores and enhance the connectivity of coal pore structures, leading to heightened permeability and decreased strength. [PERSON] et al. [15] studied the influence of gas fracturing on microcracks in coal. [PERSON] et al. [16] investigated the evolution characteristics of pore structure in coal after gas fracturing. Currently, fracturing operations commonly utilize pure gases as fracturing fluids, with CO\({}_{2}\), N\({}_{2}\), and liquefied petroleum gas (LPG) being the most prevalent options [17; 18; 19; 20]. In recent years, scholars have conducted research on various gas fracturing media. However, the underground conditions are complex, and different regions have varying geological conditions, which has led to a lack of a comprehensive consensus on gas fracturing technology to date [21; 22; 23; 24; 25; 26]. Furthermore, the physical and environmental conditions of rocks can impact the effectiveness of gas fracturing, and rocks often exhibit higher temperatures [27; 28; 29]. Therefore, it is vital to factor in the impact of temperature on the efficiency of gas fracturing, as emphasized in previous research [30; 31]. This study aimed to investigate the influence of temperature on gas pressure fracturing. To achieve this, numerical simulations were conducted to simulate and calculate the effects of temperature before and after incorporating the temperature field. Based on this, a thermal-fluid-solid-damage coupled model of reservoir gas fracturing was established using the COMSOL Multiphysics 6.0 in conjunction with research methods.