鄂西咸丰地区咸地2井上奥陶统五峰组—下志留统龙马溪组页岩沉积环境分析

Well XD-2 Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation Shale Sedimentary Environment Analysis in Xianfeng Area,Western Hubei

鄂西咸丰地区上奥陶统五峰组—下志留统龙马溪组获得了较好的页岩气发现,而沉积环境是影响页岩气生成的重要物质条件基础,影响页岩气的生成与聚集规律。通过对地质调查井咸地2井实物岩性资料分析、测井数据U、Th、K、有机碳含量特征综合分析与研究,可以较好的反映该地区上奥陶统五峰组—下志留统龙马溪组页岩沉积环境特征。综合研究表明,五峰组—龙马溪组主要岩性组合为黑色含碳页岩、炭质页岩、硅质页岩、含碳含硅质页岩、粉砂质页岩,富含笔石化石;其测井数据U、Th、K比值以及微量元素结果显示,五峰组—龙马溪组五峰组Th/U元素比值均小于2,最大值为0.75,为缺氧环境下的高还原环境的产物;有机碳含量范围0.65%~8.08%,集中值1.33%~2.13%,平均值1.95%,有机碳含量较高。因此,鄂西咸丰地区一带上奥陶统五峰组—下志留统龙马溪组页岩沉积环境主要为深水还原环境,有利于形成较好的页岩气储层。

Better shale gas resource has been found in western Hubei Xianfeng area upper Ordovician Wufeng Formation-lower Silurian Longmaxi Formation.While sedimentary environment is the essential material condition basis impacting shale gas generation.Through geological survey well XD-2 material object lithologic data analysis,well logging data U,Th,K and organic carbon content features integrated analysis and research can reflect the shale sedimentary environment features better.The integrated study has shown that the main lithologic associations of the two formations have black carbon containing shale,carbonaceous shale,siliceous shale,carbon and silicon containing shale,silty shale and rich in graptolite fossils.Their well logging data U,Th,K ratios and trace elements have shown that Th/U ratios of the two formations are all less than 2,the maximum is 0.75,which indicated oxygen deficient strong reducing environment.Organic carbon content range is 0.65%~8.08%,but concentrated within 1.33%~2.13%,average 1.95%,thus rather high.Hence the shale sedimentary environment had been mainly deep water reducing environment,thus propitious to form better shale gas reservoirs.