国内煤岩储层压力和渗透率普遍偏低, 目前矿场主要采用注入/压降测试方法来求取地层参数, 但由于注入水无法进入基质孔隙, 测试数据无法反映基质解吸特征。针对这一问题, 本文建立能够真实反映煤层气藏地层参数的三孔双渗渗流数学模型, 利用拉氏变换和Stehfest 数值反演方法对模型进行求解, 获取不同边界条件(径向无限大、外边界定压以及外边界封闭)下的直井井底拉氏空间拟压力解析解, 绘制无因次拟压力和无因次拟压力导数与无因次时间的双对数曲线, 并根据曲线特征对三孔双渗煤岩储层直井渗流阶段进行划分, 对影响井底压力响应特征的关键参数进行分析, 为煤层气的试井精细解释提供理论依据。
Most of the coal reservoirs in China are of low-permeability and low-pressure, and the injection/fall off test is usually used to correctly evaluate formation parameters. But because water molecules can't enter the matrix porosity, the adsorption and desorption characteristics of the matrix can't be reflected. Concerning this issue, a triple-porosity and dual-permeability mathematical model has been established. Accurate solution to this model under different outer boundary conditions(Infinite, no flow and constant pressure)is obtained by use of Laplace transformation and Stehfest numerical inversion. According to the analysis in Laplace domain, the type curves of dimensionless pressure and pressure derivative are graphically illustrated. The pressure decline performance under the effects of CBM reservoir properties are discussed. A theoretical basis for CBM well test has been provided.
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