京西凹陷上古生界页岩气资源潜力分析

An Analysis of Resource Potential on Upper Paleozoic Shale Gas in Depression of Western Beijing

京西凹陷经历了地台结晶基底-盖层发育-板内造山复杂构造演化三个阶段。在晚奥陶世-早石炭世处于隆起剥蚀区,自晚石炭世开始由东南向西北的海侵和早二叠纪自西北向东南海退的总趋势,其间伴有多次小规模海水进退事件的发生,使本区堆积了滨海湖沼、三角洲-沼泽相的深色泥页岩、含煤建造。地层主要分布上石炭统太原组和下二叠统山西组黑色泥页岩。本次针对太原、山西组含页岩层系开展野外调查研究,在样品测试,含气量初评的基础上,对京西凹陷上古生界页岩气资源前景进行初步评价。研究表明,本区上古生界石炭-二叠系太原组-山西组有机质丰度较高、有机质类型好、达成熟-过成熟阶段,具有页岩气形成与富集的有利地质条件,可作为京西地区上古生界的生烃层位。经采用概率体积法进行页岩气资源评价,估算其潜在资源量约为8.12×10~8m^3,表明该区域具有一定的页岩气资源勘探前景。

The Jingxi sag has experienced three stages of complex tectonic evolution that contain platform crystalline basement, caprock development and intraplate orogeny. It was in the uplift and denudation zone during late Ordovician to early Carboniferous epoch. The transgression starts from southeast to northwest since late Carboniferous and the regression starts from northwest to southeast. Meantime, many small-scale transgressive and regressive events occured. General trend of transgression and regression makes the area accumulating the dark mud shale and coal bearing construction of littoral-limnetic facies and delta-swamp facies. The formation is composed of black mud shale that mainly distributes on Taiyuan Group of Upper Carboniferous and Shanxi Group of lower Permian series. Base on geological survey, the shale gas resources are evaluated preliminarily on the basis sample tests and gas content assessment of Upper Palaeozoic Shanxi and Taiyuan Group in the depression west of Beijing. The results show that the Carboniferous strata have a wide distribution, with variable single layer thickness,well developed dark mudstones and abundant organic matter. The abundance of hydrocarbon source rocks is medium to good, and the organic matter is mainly of type Ⅱ1, the thermal evolution of organic matter has entered the high mature-over mature stage and consists mainly of dry gas. The study area has the basic geological conditions of producing shale gas. By a probability volume method, it shows that Upper Palaeozoic Shanxi and Taiyuan Group shale gas resource is of certain value for exploration development with volume of 800×10~8m^3.