高煤阶煤层气井不同排采阶段渗透率动态变化特征与控制机理

Dynamic variation characteristics and mechanism of permeability in high-rank CBM wells at different drainage and production stages

煤层渗透率动态变化规律是煤层气开发地质领域的研究热点之一。根据无因次产量分析方法,基于沁南地区15口高煤阶煤层气井排采数据,采用无因次产气率指标,将排采阶段定量划分为排水阶段、不稳定产气阶段、稳定产气阶段和衰减阶段;引用物质平衡方法,利用生产数据,计算并分析了各井不同排采阶段渗透率变化值。从渗透率变化趋势、主导机制、体系能量、相态构成和产能动态5个方面,阐释了高煤阶煤层气井不同排采阶段煤层渗透率动态变化特征与控制机理。研究结果表明,在高煤阶煤层气井排采过程中,煤层渗透率呈现降低—恢复—升高的特征;有效应力效应和基质收缩效应直接控制了煤层渗透率的变化特征;吸附与解吸特征从根本上控制了基质收缩效应的作用时间与强度。

Dynamic variation rule of coal reservoir permeability is one of the most important issues in development geologyfield of coalbed methane（CBM）. According to the method of dimensionless production analysis,the whole drainage and pro-duction process is divided into four stages as water drainage,unstable gas production,stable gas production and gas produc-tion decline based on drainage and production data of fifteen high-rank CBM wells in southern Qinshui Basin. The coal per-meability variation value at different stages were analyzed with production data by material balance method. The dynamicvariation value and mechanism of permeability in high-rank CBM wells at different drainage and production stages are in-terpreted in five aspects：permeability variation trend,leading mechanism,systemic energy,phase composition and dynam-ic productivity. The study reveals that the coal bed permeability in high-rank CBM wells show the trend of decline-recover-ing-rising during produced process. Effective stress effect and matrix shrinkage effect directly control the dynamic varia-tion characteristics of the coal reservoir permeability. Characteristics of adsorption（desorption）control the acting time andstrength of the matrix shrinkage effect fundamentally.