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以四川盆地涪陵气田主力产层上奥陶统五峰组—下志留统龙马溪组页岩为研究对象,利用改进的硅质矿物-碳酸盐矿物-黏土矿物三端元图解,对其页岩岩相类型进行精细划分。涪陵气田五峰组—龙马溪组页岩主要发育8种岩相:硅质页岩相(S)、混合硅质页岩相(S-2)、含黏土硅质页岩相(S-3)、含灰/硅混合质页岩相(M-1)、含黏土/硅混合质页岩相(M-2)、混合质页岩相(M)、含硅黏土质页岩相(CM-1)和含黏土/灰混合质页岩相(M-3)。将优势岩相定义为页岩的含气量达到特定工业标准的岩相,结合研究区开发现状,划分出2类优势岩相,即含气量大于4.0 m3/t评为Ⅰ类(特优),含气量在2.0~4.0 m3/t评为Ⅱ类(优)。筛选出有机质丰度、硅质矿物含量、黏土矿物含量3项参数与含气量作相关性分析,建立了五峰组—龙马溪组一段页岩优势岩相的分级标准,确定了研究区混合硅质页岩相(S-2)、含黏土硅质页岩相(S-3)为Ⅰ类优势岩相,含黏土/硅混合质页岩相(M-2)为Ⅱ类优势岩相。页岩优势岩相分级标准可为其他区块页岩气评价提供参考。
Taking the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation shale in the main producing layer of Fuling gas field in Sichuan Basin as the research object, this paper uses the improved three-terminal diagram of siliceous minerals, carbonate minerals and clay minerals, Rock lithofacies type finely divided. Fuling gas field Wufeng Formation - Longmaxi Group shale mainly develops 8 kinds of lithofacies: siliceous shale (S), mixed siliceous shale (S-2), siliceous shale (S-3) (M-1), clay-silica mixed shale facies (M-2), mixed shale facies (M), siliceous clay shale facies 1) and clay / ash mixed shale facies (M-3). The dominant lithofacies are defined as lithofacies whose shale gas content reaches a certain industry standard. Based on the current development in the study area, two dominant lithofacies are identified, that is, Class I (Premium) with a gas content of more than 4.0 m3 / t, Gas content 2.0 ~ 4.0 m3 / t as Class Ⅱ (excellent). Based on the correlation analysis of the three parameters of organic matter abundance, siliceous mineral content and clay mineral content with the gas content, the grading standards of shale lithofacies of the first member of Wufeng Formation-Longmaxi Formation were established, and the mixed siliceous Shale facies (S-2) and clay-siliceous shale facies (S-3) are dominant lithofacies, and clay-siliceous shale facies (M-2) is a type II dominant lithofacies. Shale dominant lithofacies classification criteria can provide reference for shale gas evaluation of other blocks.