Research on Coal Thermo-Hydro-Mechanical Coupling Model and Influence Factors

Abstract

In the coal cryogenic volume fracturing, the variations of temperature field, seepage field, and stress field of coal are the foundation to study fracture propagation in the condition of cryogenic injection. Taking 3# high-rank coal sample from Jincheng City of Shanxi Province as study object, based on coal mechanics tests and permeability tests in complete stress–strain process under cryogenic conditions, a thermo-hydro-mechanical coupling mode is introduced under the condition of low-temperature phase change and a THM coupling numerical model of high-rank coal is established. The effect of different treatment parameters, porosity, permeability, thermodynamic parameters, and coal cleat on temperature field, seepage field, and stress field during the cryogenic volume fracturing is simulated. The results show that the temperature field is mainly subjected to the influence of treatment parameters, porosity and permeability, and thermodynamic parameters of coal. As for the seepage field, it suffers the influence of both injection and mechanical parameters. In addition, the stress field is principally affected by treatment parameters, permeability, and modulus of elasticity. Additionally, cleat that exists is also able to substantially increase the influence area of cryogenic fluids on three fields mentioned above.