昭通褐煤盆地煤层气富集规律及主控地质因素

摘要

In pace with the successful commercial exploitation of CBM in Powder River Basin, USA, the CBM resources in lignite basin are widely concerned. In China, the Zhaotong lignite basin has a great deal of CBM resource with huge exploitation potential. Based on CBM distribution pattern analysis has determined main controlling geological factors for CBM enrichment, and carried out CBM re⁃source exploitation assessment. The study gas shown that the lignite in the basin has low level of evolution with less methane generated;substantial pores and fissures filled with water have caused low gas content in lignite seams;predicted gas content of lignite with buried depth 150 m is 1.45 m3/t, buried depth 500 m is 2.00 m3/t. Main controlling geological factors for CBM enrichment include lignite seam thickness, buried depth, tectonic geological features, lignite roof lithology and confining condition etc. Since the lignite has low coalifi⁃cation level with less methane generated;together with lignite buried depth is not large, susceptible to be oxidized, caused low lignite gas content. But lignite is thick in the basin with large resources and high CBM abundance per unit area thus provided with excellent in⁃ternal conditions. Meanwhile, postsedimentary structure is relatively stable;lignite roof is clay and sandy clay with good confining con⁃dition, thus in favor of CBM preservation.%随着美国粉河盆地煤层气商业开发的成功，褐煤盆地煤层气资源受到广泛关注。我国昭通褐煤盆地蕴藏着丰富的煤层气资源，开发潜力巨大。在分析煤层气分布规律的基础上，厘定了煤层气富集的主控地质因素，对煤层气资源开发潜力进行了评价。研究表明：昭通盆地褐煤演化程度低，煤层生气量少，且大量孔裂隙被水充填，煤层含气量低，预测埋深150 m煤层气含量为1.45 m3/t，埋深500 m煤层气含量为2.00 m3/t。研究区煤层气富集的主控地质因素包括煤层厚度、煤层埋藏深度、构造地质特征、煤层顶板岩性及封闭条件等。由于褐煤煤化程度低，煤层生气量少，加之盆地内煤层埋藏深度不大，易遭受氧化，致使煤层含气量较低，但盆地内煤层厚，赋存的煤炭资源量大，单位面积内煤层气资源丰度高，为煤层气富集提供了良好的内部条件；同时盆地沉积后期构造相对稳定，煤层顶板为粘土及砂质粘土，封闭条件较好，有利于煤层气的保存。