鄂尔多斯韩城地区石炭-二叠系含煤沉积体系及其控气作用

摘要

The geological conditions for coalbed methane are complicated in Hancheng area of the Ordos Basin. The characteristics of coal-bearing depositional system work as the main controlling factor for the enrichment of coalbed methane. According to the features of coal-bearing sediments in Carboniferous and Permian in Hancheng area, the Taiyuan Formation constitutes of lagoon-tidal-barrier island sedimentation and carbonate flat sedimen-tation while the Shanxi Formation constitutes of fluvial-dominated delta sedimentation. The changes of sedimenta-tion, the thickness of coalbed, the petrophysical property and the lithology of roof and floor of coalbed are direct-ly concerned to analyze the influence of sedimentary environment on CBM enrichment. The coalbed no.3 is thin and even pinches out locally. The coalbed no.5, which is thick and stable, is widespread in the study area. The roof and floor of coalbed are mainly mudstone, sandstone and siltstone. The coalbed with stable structure and thick mudstone as roof and floor is favorable for the enrichment and accumulation of coalbed methane. The area to the east of Baimatan town is the exploration target for 2 sets of coalbed.%鄂尔多斯韩城地区煤层气地质条件复杂，含煤沉积体系特征是影响煤层气富集的重要因素之一。通过对韩城地区石炭-二叠系含煤沉积特征的研究，发现太原组主要为潟湖-潮坪-障壁岛沉积和陆表海碳酸盐岩台地沉积，山西组主要为河控三角洲沉积。从主要可采煤层的沉积相变、煤层厚度变化、煤岩物性变化及煤层顶底板封盖特征方面分析了沉积作用对煤层气富集的影响。研究表明：3号煤厚度较小，甚至出现变薄尖灭的现象；5号煤在全区发育且厚度较大，横向连续性好。煤层顶底板主要以泥岩、砂岩、粉砂岩为主，其中以厚层泥岩为顶底板的结构稳定的煤层更有利于煤层气的富集成藏。白马滩镇以东地区为2套煤层的有利开发区块。