内蒙古东南部林西组页岩气聚集地质条件

Geological Accumulation Conditions for Linxi Formation Shale Gas in Southeastern Inner Mongolia

内蒙古东南部地区油气勘探程度低,上古生界林西组分布面积广,厚度大,广泛发育暗色泥岩。受大地构造背景控制,该地区林西组被火山岩分隔呈NE—SW向条带状发育出露。页岩分布在平面上存在东部陶海和西部官地2个厚度中心,累计可达700m以上。林西组页岩以Ⅱ2—Ⅲ等腐殖型干酪根为主;有机质丰度中等,露头页岩样品平均TOC值多分布在0.5%～1.0%之间,鲁D1井等局部地区TOC值也可超过1.5%;有机质热演化程度相对较高,镜质体反射率（RO）通常超过2%;伊利石结晶度实验表明该页岩处于晚成岩阶段。微观薄片和扫描电镜观察到溶蚀孔、粒间孔和有机质孔等发育。X-衍射分析页岩中的石英和斜长石等脆性矿物含量高,黏土含量一般小于40%,且以伊利石和伊/蒙混层为主组成。综合分析认为该地区有一定的页岩气资源潜力,较有利地区分布在昆都—扎鲁特地区,但进一步勘探需结合重磁力、电法等辅助资料进行综合研究。

Southeastern Inner Mongolia is a new region for petroleum exploration,where developed massive dark shale in Linxi Formation in Neopaleozoic. The overall thickness of Linxi shale can exceed 700m and the maximum thickness distributed in Taohaiyingzi to the east and Guandi to the west. The kerogen type is Ⅱ2-Ⅲ and the organic richness is moderate with average TOC mainly between 0. 5%-1. 0%. TOC over 1.5% only exists regionally. The thermal maturity is high with vitrinite reflectance （Ro） over 2.0% and the shale is at late diagenetic stage according to the analysis of illite crystallinity. The erosion pores,interg- ranular pores and organic pores can be observed with the optical microscope or SEM. Brittle minerals such as quartz and plagioclase dominate and clay consisting of mainly illite and mixed-layer illite/smectite is less than 40 %. Overall, shale gas potential for Linxi shale exists and the favored regions for shale gas accumula- tions locate on Kundu-Zhalute areas. However, more materials such as gravity, magnetism and electrical methods are needed when it comes to next step exploration.