沁水盆地晚古生代含煤沉积体系及其控气作用

Coal Depositional System and Its Controlling Role of Coalbed Methanein Late Paleozonic of Qinshui Basin

沁水盆地晚古生代含煤地层主要为晚石炭世太原组和早二叠世山西组,可采煤层有太原组第15号煤层和山西组第3号煤层,两者均为高煤阶无烟煤。对含煤地层内部各成因相及其组合的综合分析表明,太原组为陆表海多堡岛与碳酸盐台地复合沉积体系。第15号煤层形成于海退持续时间较长的潮汐三角洲环境,其中三角洲平原沼泽相中煤层较厚,滞留泻湖相中煤层较薄,障壁沙坝一带煤层厚度较稳定。山西组为河控三角洲沉积体系。三角洲平原沼泽环境中均衡补偿沉积持续时间较长,形成的第3号煤层厚度较大,结构简单。三角洲前缘沙坝中煤层厚度稍薄,分流河道中煤层不稳定。煤层气勘探实践表明,在同一口试气井中,盆地内大部分地方第3号煤层比第15号煤层厚度大,生气能力强,煤层气保存条件优越,气体质量浓度、含气饱和度、煤层气资源量高。因此,第3号煤层应是沁水盆地煤层气试采和商业化开发的首选目标层。

The main coal-bearing strata in the Qinshui Basin are late Carboniferous Epoch Taiyuan Formation and Early Permin Epoch Shanxi Formation. The No. 15 coalbed of Taiyuan Formation and No. 3 coalbed in Shanxi Formation, belonging to premium anthracite, are workable seams. Multidisciplinary analysis on genetic facies and their assemblage shows that Taiyuan Formation is made up of epeiric sea barrier island depositional systemcarbonate plateau system, No. 15 coalbed was formed in tidal delta environment which sustaining a long time of marine regression, and the thickness of No. 15 coalbed is thicker in bog of delta plain, thinner in stagnant barchans and stable in barrier bar. Shanxi Formation constitutes of fluvial-dominated delta depositional system, and No. 3 coalbed formed is thicker and simple in structure because isostatic compensational deposit lasted for a long time. But the coalbed formed in delta front bar is thinner and is unstable in distributary channel. Indicated by exploratory of coalbed methane in the Qinshui Basin, No. 3 coalbed is thicker, the source abilixy is stronger, preservative condition of coalbed methane is more ascendant, and volume concentration, saturation, resource quantity of coalbed methane is higher than these of No. 15 coalbed in the same pilot well. Therefore, No. 3 coalbed should be the picking target stratum for producing test and commercial exploration of coalbed methane.