The Influence of the Injected Water on the Underground Coalbed Methane Extraction

Abstract

The increasing demand on coal production has led to the gradually increase of mining depth and more high methane mines, which bring difficulties in terms of coalbed methane (CBM) extraction. Hydraulic fracturing is widely applied to improve the production of CBM, control mine gas, and prevent gas outbursts. It improves coal bed permeability and accelerate desorption and migration of CBM. Even though the impacts of hydraulic fracturing treatment on the coal reservoirs are rare, negative effects could not be totally ignored. To defend this defect, the presented work aims to study the influence of water filtration on coal body deformation and permeability evolution. For this purpose, a simulation based finite element method was developed to build a solid-fluid coupled two-phase flow model using commercial software (COMSOL Multiphysics 5.4). The model was verified using production data from a long strike borehole from Wangpo coal mine in Shanxi Province, China. Several simulation scenarios were designed to investigate the adverse impacts of hydraulic fracturing on gas flow behaviors. The mechanisms of both relative and intrinsic permeability evolutions were analyzed, and simulation results were presented. Results show that the intrinsic permeability of the fracture system increases in the water injection process. The impacts of water imitation were addressed that a critical time was observed beyond which water cannot go further and also a critical pressure exists above which the hydraulic pressure would impair the gas flow. Sensitivity analysis also showed that a suitable time and pressure combination could be observed to maximize gas extraction. This work provides an efficient approach to guide the coal bed methane exploitation and other unconventional gas reservoirs.

Coal Mine Fire Emergency Rescue Capability Assessment and Emergency Disposal Research

“…Nowadays, underground accidents in coal mines are frequent, causing huge casualties and economic losses. The majority of these accidents are caused by fire-induced gas explosions, with the severity of death reaching more than nine people per fire accident, and the severity of death in all other accidents is less than that of fire accidents, so coal mines need to pay sufficient attention to fire [4][5][6]. In recent years, China's coal enterprises also generally pay attention to the prevention of coal mine fire accidents, and the construction of a major disaster prevention and protection system for China's coal enterprises has gone through five stages: passive prevention, traditional empirical prevention pre-prevention post-prevention, systematic prevention and protection, and systematic scientific management [7][8][9].…”

Optimization of Accurate Spacing for Gas Extraction from Damaged Coal Seams Based on a Dual-Penetration Model

“…Duan et al [14] carried out mechanical and seepage experiments on laminated coal seams in order to study the effects of structural anisotropy and stress state on permeability evolution, derived a dynamic anisotropy (D-A) permeability model, and investigated the effects of different initial permeability anisotropy ratios on the effect of gas extraction. Liu et al [15] established a solid-flow coupled two-phase flow model, investigated the effects of residual filtrate water on the deformation and permeability evolution of a coal body after hydraulic fracturing, used COMSOL to simulate the coupled numerical solution under negative pressure pumping conditions and permeability evolution, and analyzed the evolution mechanism of relative permeability and intrinsic permeability. Based on the softening model and diffusionpermeability theory, Wang et al [16] established the permeability and gas flow equations of penetrating borehole cavern-making and optimized the borehole cavern-making unloading and penetration enhancement technology using COMSOL simulation.…”