煤层气渗流方程及数值模拟

COAL-BED METHANE PERCOLATION EQUATION AND ITS NUMERICAL SIMULATION

中国煤层气资源丰富 ,据估算 ,埋深 2 0 0 0m以浅的煤层气资源达 (30～ 35 )× 10 12 m3 。但中国煤层气地面开发刚进入起步阶段 ,加之中国煤田地质条件比较复杂 ,因此研究中国特殊地质条件下煤层气的解吸、扩散和渗流机理的具体地质表现是认识煤层气可采性的关键。针对我国煤层气开采的特殊性 ,我国采取“地面开采和井巷抽放相结合”的方针。然而井巷开采占了相当的比例。本文建立了煤层气扩散渗流数学物理方程 ,并对煤层气渗流偏微分方程 ,采用差分法 ,进行了数值模拟计算。模拟结果表明 ,所建立的煤层气扩散渗流模型较准确地反映了煤层中煤层气流动规律 ,模拟后的煤层气压力变化曲线可以确定煤层气的开采压力变化范围和煤层气产气最大面积 ,对我国大面积低渗透性无烟煤煤层气的开发具有指导意义。

China is rich in coal bed methane resources,the total coal bed met hane resources within a depth of <2 000 m being estimated at 30～50×10 1 2 m 3.In China,however,the coal bed methane development at surface is just entering into its initial stage and the geological conditions of coal fields are very complicated,so that it is the key to exploit coal bed methane to study t he mechanisms of coal bed methane's desorption,diffusion and percolation flow u nder the special geological conditions of the coal fields.In light of the partic ularity of coal bed methane exploitation in China,a policy of ' combining expl oitation at surface with tunnel drainage' has been adopted,the tunnel drainage accouting for a considerable proportion.In the paper,a math physical equation o f coal bed methane diffusion /percolation is established and a numerical simul ation calculation is finished up for the partial differential equation of coal bed methane percolation flow by use of difference method.The simulation result s hows that the coal bed methane flow law can be exactly reflected by the coal b ed methane diffusion/percolation model established;and the range of producing p ressure change and the areas with maximum coal bed methane production may be de termined by the coal bed methane pressure change curve simulated,which is of gr eat significance for coal bed methane development of low permeability anthraci te coal beds occupying a large area in China.