应力敏感性复合煤层气压力动态特征

PRESSURE TRANSIENT RESPONSE IN COMPOSITE COAL SEAM WITH DOUBLE POROSITY

煤层气采出有扩散和渗流两个过程,比常规天然气层中的渗流方程复杂。针对煤层气井在钻井、完井、开采过程中井周围产生污染带以及地层本身的非均质情况,采用非平衡态吸附模型,研究应力敏感性复合煤层气藏的流动规律。在拟稳态流的数学模型假设下,用气体拟压力代替Langmuir吸附公式中的压力,得到气层中拟压力所满足的方程组,并采用正则摄动法和Laplace变换法进行求解,最后通过拉氏数值反演得倒0阶摄动解。分析了参数变化时压力动态的变化规律,这些结果为煤层气藏开发提供了理论依据和新的试井模型。

Coal-bed gas migration includes two stages,i.e.diffusion and percolation,so the equations describing coal-bed gas are much complicated than that describing the percolation flow in conventional gas reservoir.Aimed at the pollution bond and the non-homogeneous character of the reservoir itself which happened during the drilling,well completing and the developing process,the single-phase flow rule of coal-bed gas in coal and cleats may be studied by use of non-equilibrium adsorption model.Under the assumption of the mathematical models of the pseudo-steady state,and equation of meeting the needs of the pseudo-pressure in coal-bed gas may be obtained by use of the pseudo-pressure to replace the pressure in Langmuir adsorption formula.The models may be solved by use of Laplace transform and the solution can be obtained through numerical inversion.In the paper,the change rule of pseudo-pressure along with composite dual media parameters is discussed.All of these results have provided a theoretical basis and new test model for coal-bed methane reservoir development.