重庆地区下古生界页岩气聚集条件及有利区预测*

重庆地区是中国页岩气勘探开发取得突破的地区,页岩气赋存层位主要为下古生界上奥陶统五峰组—下志留统龙马溪组有机质泥页岩。依据露头、钻井岩心及测井资料,利用沉积学、有机地球化学等方法,分析研究区泥页岩沉积学特征与岩石学特征、页岩气聚集条件,并预测区内页岩气有利区。结果表明,区内暗色泥页岩厚度大,分布广,总有机碳含量大于2%,有机质类型以Ⅰ型为主,热演化程度处于高成熟—过成熟阶段,说明该区泥页岩具有很好的生烃潜力;区内页岩气层上覆厚层泥页岩与下伏岩层灰岩对页岩气具有较好的保存效果;泥页岩含气量较高,平均为1.39,cm³/t。采用综合信息叠合法,可预测研究区页岩气发育有利区位于城口—巫溪一带与石柱—涪陵—武隆—彭水—南川—綦江一带。

Accumulation conditions and strategic selection of favorable areas of shale gas of the Lower Paleozoic in Chongqing area

Chongqing area is the breakthrough area of shale gas exploration and development,and the shale gas is preserved in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation of the Lower Paleozoic. Based on data from outcrop,drilling core and logging data, using sedimentology,organic geochemistry and other methods, the characteristics of sedimentology of shales,and the shale gas accumulation conditions was analyzed and the favorable areas for shale gas exploration of study area were predicted. The results showed that the dark shale in Chongqing area had a great thickness and a broad distribution, with the content of total organic carbon being more than 2% and the organic matter type being type I. The thermal evolution was in high mature-over mature stage which indicated the shale have a better hydrocarbon￣generating potential. The target dark shale horizon was overlain by a thick sequence of shales and underlain by thick modular limestones and micritic limestones, which provided a deal preservation effect for shale gas. The content of gas was much higher and the average gas content being 1.39,cm³/t. The integrated information overlapping method was used to predict favorable areas of shale gas exploration, and two favorable areas were predicted, including the Chengkou-Wuxi area and the Shizhu-Fuling-Wulong-Pengshui-Nanchuan-Qijiang area.