Modelling And Numerical Simulation On Gas Driven By Water Injection In Coal Bed

Enhanced gas recovery by water injection is a simple and effective way for gas production, in which the fluid-solid interaction in porous media plays an important role. If enhanced gas recovery by water injection technology is used reasonably, efficiency of gas production would be improved and safety construction would be ensured during the mining process. In this process, the involved fluid-solid interaction for multiphase flow is a very complex problem. In order to improve mining environment and utilization efficiency of natural gas, the basic research on fluid-solid interaction for multiphase flow is investigated. For most of nowadays studies of fluid-solid interaction, Eulerian method is often applied to describe fluid transport, the Lagrangian method is adopted to describe solid motion. Besides, Lagrangian method is also used to describe both fluid and solid motion in meshfree method. In this work, Eulerian method is adopted to describe both the fluid and solid motion, and the Finite Volume Method is introduced to discretize the governing equations for fluid and solid uniformly.In this thesis, the coupling of fluid and solid in mining process is described by Eulerian method and the governing equations are discretized by Finite Volume Method(FVM). Firstly, coal bed is treated as porous media, and a mathematical model for multiphase flow in porous media with fluid-solid coupling is set up. The fluid-solid coupling force is introduced as an external force term in governing equations. Moreover, the dimensionless governing equations are derived. Then the coupling problems of fluid and solid for gas recovery by water injection are simulated numerically, and the analyses based on simulated velocity and pressure fields for fluid and strain field for solid are made.Conclusions can be drawn from the present numerical results that:(1) the simulated results based on the build mathematical model in this thesis coincides qualitatively with the experimental results, and the qualitative analysis based on the mathematical model built in this paper is reasonable although there exist numerical errors in comparing with experimental result, many factors, such as ignoring the effects of gas adsorption and desorption effects, maybe the reason to cause errors.(2) With different inlet velocities and different distance between inlet and outlet, the results demonstrate that the stress, porosity and the coal strain increase with the inlet velocity and the distance between inlet and outlet.(3)There are three regions where solid stress and strain are larger than others, including the entrance, the contact points of the water and the upper wall, and the contact position of the water on the left side. The same two dangerous regions were reported in experimental research.(4) In addition, there is relative larger stain in the region where water flows through.