Numerical methods of hydraulic fracturing in porous media such as coal seam or shale rock can be generally divided into classified into continuous and discontinuous methods. Therefore, under the background of huge economic benefits and corresponding risks brought by hydraulic fracturing, many numerical methods for predicting the effect of hydraulic fracturing in porous media have emerged. However, it is controversial because of the leakage of fracturing fluid or gas and the pollution of groundwater caused by hydraulic fracturing. Hydraulic fracturing is often used to enhance the permeability of coal seams and promote the effective exploitation of coalbed methane. In recent years, with the vigorous exploitation of coalbed methane resources and the improvement of extraction technology, to a certain extent, the global energy shortage situation has been alleviated, and the incidence of coal mine gas accidents has also been greatly reduced. Numerical examples show that the proposed coupling modeling method can not only simplify the calculation steps of the CwM method and reduce the numerical errors caused, but also characterize the damage, porosity, permeability, and extraction effect caused by hydraulic fracturing in coal seams with permeability anisotropy. Additionally, two 2D numerical examples are used to verify the precision of this method, and a 3D coalbed methane extraction simulation is performed to analyze the extraction effects and the evolution characteristics of the permeability before and after hydraulic fracturing. The method is implemented by the combination of different modules in COMSOL to solve the state damage variable, displacement, and pressure. Then, the results of hydraulic fracturing simulation are used as initial values to perform coupling modeling for coalbed methane extraction. Based on the damage mechanics theory, we introduce a state damage variable to record the damage changes at different times and construct the coupling governing equations of the seepage field and solid mechanics field in the hydraulic fracturing process.

This paper proposes an improved coupled modeling method for coalbed methane extraction after hydraulic fracturing.

After effect 2018 crack