流固耦合作用下注气开采煤层气增产规律研究

提高低渗透煤层气产量是我国煤层气开采中急需解决的关键问题，加速煤层甲烷解吸过程的注气增产方法是提高低渗透煤层气产量的有效途径。由于排采降压在孔隙流体压力变化的范围内会引起储层孔隙介质的应力和应变的变化，造成有效渗透率和孔隙度的降低，同时也影响注气和产气的动态参数。研究这些规律，首先建立了注气开采煤层气多组分流体扩散渗流的流固耦合模型，利用数值方法研究了注气开采煤层气的增产机理。研究表明，注入二氧化碳气体不但减少了煤层甲烷的分压．加速了煤层甲烷的解吸；而且二氧化碳气体比甲烷气体更易吸附，竞争吸附置换煤层甲烷分子，从而提高了煤层气产量，同时必须重视耦合作用对注气增产造成的不利影响。

Study of Exploitation Coalbed Methane by Gas Injection in Fluid-solid Coupling Flow

Exploitation coalbed methane by gas injection is effective method of improving low permeability coalbed methane production. Coalbed reservoir is depleted, stress and strain of coalbed porous medium are changed because of changing of fluid pressure gradient, and result in effective permeability and porosity become lower, and production are decreased because of fluid-solid coupling effect. A dual porosity media fluid-solid coupling mathematical model of exploitation coalbed methane by gas injection is established. The nonlinear mathematical model is investigated by using finite different method and got some valuable conclusions: Improved recovery of methane from coalbed can be achieved by injection of carbon dioxide. There are two main mechanisms that aid recovery of the coal beds methane content. Firstly, by reducing the partial pressure of the methane present in the fracture, the diffusion from the coal is enhanced, the second mechanism is the competitive adsorption of carbon into the coal matrix. Molecules of CO2 preferentially absorb on to the surface adsorption sites, displacing methane, and exploitation coalbed methane by gas injection should note the fluid-solid coupling disadvantageous influence.