沁水盆地盖层对煤层气富集的影响

CAP ROCK INFLUENCE ON COALBED GAS ENRICHMENT IN QINSHUI BASIN

从煤层气藏封盖机理探讨开始,分析了沁水盆地以及其他含煤盆地煤层气富集与盖层的关系。研究认为,实际上盖层对煤层气的保存同样重要,煤层气藏对盖层封盖性的要求就是要使煤层能够达到最佳的吸附量或含气量。研究结果①良好的盖层条件可以减缓煤层气的散失,同时可间接抑制煤层气的解吸;②具有封盖性好的上覆盖层(顶板)和下伏隔层(底板)的煤层有利于煤层气的富集;③煤层埋藏太浅,盖层封盖条件变差,不利于成藏;④埋深适中,具有稳定分布、封盖性好顶底板的煤层有利成藏。沁水盆地盖层与含气量的关系说明,盖层厚度大、泥质含量高、高突破压力和一定的埋深对煤层气的保存是有利的。

Starting from discussing the seating-capping mechanism of coalbed methane reservoirs and combining the relationship between coalbed methane enrichment and cap rocks of other coal-bearing basins in China, Qinshui Basin is emphatically analyzed in this paper. In fact, the cap rock of coalbed methane plays the same important role in gas preservation respect as that of other gas reservoirs and is required to make coalbed having best adsorptive power and methane-bearing capacity. The analysis result shows; 1 favorable cap rock conditions can retard Coalbed methane scattering and indirectly restrain methane desorbing; 2 the coalbed with good sealing-capping property of overburden (roof) and low isolation layer (bottom plate) is favorable to coalbed methane enrichment; 3 too shallow burial depth and worse sealing-capping conditions are unfavorable to reservoiring. The coalbed with suitable burial depth, the roof and bottom plate of stable distribution and good sealing-capping property is favorable to reservoiring. The relationship between cap rock and methane-bearing capacity in Qinshui Basin shows that big thickness, high mud content, high broken pressure and suitable buried depth are favorable to coalbed methane preservation.