鄂西宜昌斜坡带五峰组—龙马溪组页岩优势岩相及其生气潜力

张保民; 陈孝红; 蔡全升; 陈林; 张国涛; 李培军

doi:10.2029/gc20220318

鄂西宜昌斜坡带五峰组—龙马溪组页岩优势岩相及其生气潜力

Dominant shale lithofacies and gas generation potential analysis of the WufengLongmaxi Formation in the Yichang slope area, Western Hubei Province

摘要

摘要:
研究目的 不同页岩岩相的矿物组分、含气性和可压性等的差异，决定不同岩相的开发潜力不同，页岩岩相的划分及评价对找寻页岩气勘探开发甜点具有重要指导意义。
方研究法 基于钻井、岩心和分析测试资料，综合利用地质理论结合硅质矿物-黏土矿物-碳酸盐矿物含量三端元图解，对鄂西宜昌斜坡带上奥陶统五峰组—下志留统龙马溪组下段含气页岩岩相进行划分，结合有机碳含量、含气量、岩心镜下特征等划分优势岩相。优选有机质丰度、硅质矿物含量、黏土矿物含量3项指标与页岩含气量进行相关性分析，建立了五峰组—龙马溪组含气页岩优势岩相的分级标准。
研究结果 研究区优势岩相均为II类优势岩相，II₁类(最优)优势岩相为S-2混合硅质页岩相和S-3含黏土硅质页岩相，位于龙马溪组一亚段和五峰组上段，厚6 m；II₂类(次优)优势岩相为S硅质页岩相，位于五峰组下段，厚4 m。
结论宜昌斜坡带和涪陵地区具有相似的岩相垂向演化序列，优势岩相均位于五峰组—龙马溪组一亚段，但同一岩相组合的页岩厚度和品质差异较大，发生在鲁丹阶早期的湘鄂西水下隆起和鲁丹阶晚期的水下隆起是造成宜昌地区优势岩相的厚度和品质均要差于涪陵地区的主要原因。

Abstract:
This paper is the result of oil and gas exploration engineering.
Objective The differences in mineral composition, gas content and compressibility of shale lithofacies determine the development potential of shale gas. The division and evaluation of shale lithofacies is important to identify the sweet spot for shale gas exploration and development.
Methods Based on drilling, core analysis, and test data, the comprehensive utilization of geological theory combined with ternary diagram of siliceous mineral, clay minerals, and carbonate mineral content are used to divide the gasbearing shale lithofacies of the Wufeng Formation and the lower part of Longmaxi Formation in Yichang slope of western Hubei province. The dominant lithofacies are also divided combining with the organic carbon content, gas content, and microscopic characteristics. The correlation between the abundance of organic matter, the content of siliceous minerals, the content of clay minerals and the shale gas content are carried out to establish the classification standard of gas-bearing dominant lithofacies of Wufeng-Longmaxi Formation.
Results The dominant lithofacies in the study area is type II. The type II₁ (optimal) dominant lithofacies are mixed siliceous shale facies (S-2) and clay-bearing siliceous shale facies (S-3), located in the first sub-member of Longmaxi Formation and the upper member of Wufeng Formation, with thickness of 6 m. The type II₂ dominant lithofacies (suboptimal) is siliceous shale facies (S), located in the lower member of Wufeng Formation, with thickness of 4 m.
Conclusions The Yichang slope belt and Fuling area have similar vertical evolution sequence of lithofacies, and the dominant lithofacies are both located in the Wufeng Formation and first sub-member of Longmaxi Formation. However, the thickness and quality of same shale lithofacies association are quite different. The subaqueous uplift of western Hunan and Hubei in the Rhuddanian stage is the main reason that caused the thickness and quality of the dominant lithofacies in Yichang area poorer than that in Fuling area.

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