# Dynamic Mechanical Properties of Heat-Treated Shale under Different Temperatures
## 1 Introduction  
Deflagration fracturing technology [1], also known as high-energy gas fracturing (HEGF) technology, is a unique oil and gas field stimulation technology [2]. The advantages of HEGF technology applied to rocks are as follows: First, stress waves can lead to the formation of multiple radial fractures that communicate with natural fractures. High temperatures and high-pressure gases can effectively extend the fractures and increase the content of shale gas flowing into the wellbore to a large extent. Second, deflagration fracturing is suitable for fracturing stimulations of liquid-sensitive oil and gas reservoirs. Third, the fracture itself is cut, resulting in the dislocation between layers to form support, so the fracture is not easy to close; fourth, in the actual project, deflagrant compression cracking does not require too much large equipment, which can meet the requirements of economic practicality; fifth, as a waterless fracturing technology, detonation fracturing has achieved a better environmental protection effect. HEGF generally forms a pre-fracture through perforation, and then injects a liquid drug into the perforation section to generate a large amount of high-temperature and high-pressure gas after ignition, which exerts an effect on the pre-fracture and further expands and extends it, as shown in Figure 1a. According to the physical model, thegeometric model of fracture propagation in high-energy gas fracturing of horizontal wells is defined, as shown in Figure 1b. \(\sigma_{\rm H}\) is the maximum principal stress, \(\sigma_{\rm h}\) is the minimum principal stress, L is the reservoir length, W is the reservoir width, and P\({}_{\rm t}\) is the gas pressure distribution in the fracture [3]. In terms of shale mechanics research, [PERSON] et al. [4; 5; 6] introduced a series of shale formations and analyzed their series mechanical parameters via heating. It was found that the shale has strong anisotropy and that the temperature has an obvious influence on the anisotropy, porosity, and permeability of the shale. The heating of the shale significantly reduces the strength, stirring speed, and sound velocity of the shale, and tests from other relevant scientific procedures have concluded that the shale may cause changes in the interlayer structure due to pressure and temperature unloading. Based on this, a physics-based micromechanical model was created in order to quantify the damaged state of shale under loading through macroscopic measurements. [PERSON] et al. [7; 8] found that the volume strain of shale mainly comes from compression deformation through the experiments of compressibility and triaxial compression tests of shale under different confining pressures and loads. The transition to dilatancy only occurs in the region close to the peak stress. Increasing the magnitude of the isotropic stress field has little effect on the velocity anisotropy. [PERSON] et al. [9] studied shale with different bedding (0\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\)) and conducted a study through the triaxial SHPB test with a confining pressure of 0\(\sim\)15 MPa. It was found that the dynamic mechanical properties of shale mainly depend on the interaction between bedding dip angle and various confining pressures. [PERSON] et al. [10] used the split Hopkinson pressure bar test to study the dynamic compressive mechanical response of shale specimens with five different bed dip angles after heat treatment at 25-200 \({}^{\circ}\)C. It was found that with the increase in heat treatment temperature, the failure mode of samples with bedding dip angles of 45\({}^{\circ}\) and 60\({}^{\circ}\) were significantly affected, but the bedding dip angles of 0\({}^{\circ}\), 30, and 90\({}^{\circ}\) were not fundamentally changed.