鄂西地区上奥陶统五峰组—下志留统龙马溪组页岩含气性特征及保存条件

上奥陶统五峰组—下志留统龙马溪组为鄂西地区重要的页岩气勘探目的层。利用鄂西地区20多口调查井资料，对其五峰组—龙马溪组岩性、沉积相、含气性特征及保存条件进行了分析。五峰组以黑色含碳硅质页岩为主，为深水硅泥质陆棚相，龙马溪组以灰黑色碳质页岩为主，为深水泥质陆棚相；五峰组—龙马溪组与下志留统新滩组下部组成2个三级层序且含气量符合TST1 > TST2 > HST2 > HST1的特征，五峰组含气性略好于龙马溪组，天阳坪断裂以北及咸丰断裂带以东含气量好，由于多数钻井处于深水陆棚相，沉积相对含气性的平面差异影响较小；目的层顶板下志留统新滩组粉砂质泥岩和底板奥陶系致密灰岩横向分布稳定，为区域良好盖层；五峰组—龙马溪组埋藏史可以划分为4个阶段，与四川盆地相比鄂西地区的埋藏史呈现“抬升时间偏早”和“抬升速率过快”的特征。埋深、距离正断层的远近对含气性有一定影响，但断裂和褶皱的匹配样式是影响含气量高低的最关键因素，远离正断层且位于向斜核部或翼部，离正断层较远、位于断层下盘且上倾方向未与断裂沟通这2种构造样式有利于页岩气的聚集成藏。 

Gas-bearing characteristics and preservation conditions of Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in western Hubei

The Upper Ordovician Wufeng to Lower Silurian Longmaxi formations are important exploration targets for shale gas in the western Hubei province. The lithology, sedimentary facies, gas-bearing characteristics and preservation conditions of the Wufeng-Longmaxi formations were analyzed with the samples of more than 20 survey wells. The Wufeng Formation is dominated by black carbonaceous siliceous shale of deep-water siliceous argillaceous shelf facies, while the Longmaxi Formation is dominated by gray-black carbonaceous shale of deep-water argillaceous shelf facies. The Wufeng-Longmaxi formations and the lower part of Lower Silurian Xintan Formation consist of two three-level sequences, and the gas content conforms to the characteristics of TST1 > TST2 > HST2 > HST1. The gas content of the Wufeng Formation is slightly higher than that of the Longmaxi Formation. A good gas potential has been found to the north of Tianyangping Fault and the east of Xianfeng Fault. Since most wells were in the deep shelf facies area, sedimentary facies have little effect on the plane distribution of shale gas content. The studies of preservation conditions showed that both the Xintan Formation as the roof and the Ordovician as the floor have good sealing properties. The burial history of Wufeng-Longmaxi formations can be divided into four stages, and shows the characteristics of “early uplift time” and “rapid uplift rate” when compared with the Sichuan Basin. The burial depth and the distance to normal fault have certain influence on the gas content. However, the matching pattern between fault and fold is the most important factor affecting gas content. Two structural patterns are beneficial to shale gas accumulation, one is being far away from normal fault and locating at the syncline wing or core, the other is being far away from normal fault and locating at the footwall of fault and the target stratum is not connected to the fault in the up-dip direction.