Study Of Gas-solid Coupling Seepage Flow In Coal Containing Methane And Its Application

Rockburst in coal seam containing methane is a kind of complex and dynamicdisaster, and it hinders the mine safely that is a big problem for coalmine. The stressfield and the seepage field of methane react upon one another in the process ofrockburst, thus it is important to research the coupling effect between stress field andseepage field to reveal the mechanism of rockburst in coal seam containing methane.This dissertation focuses on the law of failure and deformation of coal and seepage ofmethane. According to the seepage theory for methane and damage mechanics theoryfor coal, the coupling mechanism is investigated by using theoretical modeling andnumerical simulation. The main results are listed as following.(1) The dual-porosity model is applied to describe the characteristic of porousmatrix and fracture structure in coal based on the feature of coal structure. On thebasis of deformation characteristics of coal matrix under stress, the couplingrelationships for both porosity and permeability with stress are built. The law ofclosure of fracture under compression and dilation under shearing are analyzed basedon the structure characteristics of single fracture in fracture system. In addition, thedeformation model of fracture is built, and then the coupling relationships for bothporosity and permeability with stress in fracture system are obtained based on thecubic law.(2) The swelling and shrinkage strain induced by methane adsorption anddesorption are obtained according to the theory of physical chemistry of coal surfaces.The swelling and shrinkage strain have a strong effect on the effective stress due tothe particular structure of coal matrix separated by fracture. Effective stress equationfor coal containing methane is built which considering the influence of swelling andshrinkage stress. Since volumetric strain describes the development of fracture,damage evolution equation for coal is built by accounting volumetric strain as aninternal factor. Mohr-Coulomb failure criterion is adopted as criterion of criticaldamage. Then the strain is corrected through plastic corrections after shear failure ortensile failure occurs. Meanwhile, strain-softening model for cohesion of coal is builtby analysis of the characteristic of cohesion decreasing with the increase of strain.(3) Equations of mass conservation for methane in both matrix system andfracture system are built based on the seepage pattern and equations of states.Numerical simulation software named TOUGH2(CH4) for methane seepage is developed by rewriting the code of TOUGH2. Then the rationality of this software isverified by a small simulation of methane seepage in coal sample. The damage modelfor coal is written in C++, and compiled as a DLL file that can be loaded by FLAC3Dwhen it runs. The process of coal sample under compression is simulated based onFLAC3D with loading the new defined model. The simulated result reflects reality ofdamage process of coal accurately. In order to run a coupled simulation for theanalysis of gas-solid coupling, TOUGH2(CH4) and FLAC3D simulation arecollaborated as TOUGH2(CH4)-FLAC with TOUGH-FLAC code which is a coupledcode linking two existing simulators (TOUGH2and FLAC3D). The accuracy of newcoupling simulator is proved by a numerical model for calculation of methane seepagein coal sample under confining pressure.(4) TOUGH2(CH4)-FLAC is implemented into a field case in Hegang-Nanshancoal mine. The simulations focus on the damage evolution of surrounding rock andmethane seepage. The simulation results reveal the mechanism of extreme gasemission after disturbance induced by rockburst.