测井资料用于页岩岩相划分及识别——以涪陵气田五峰组—龙马溪组为例

Shale lithofacies identification and classification by using logging data:a case of Wufeng-Longmaxi Formation in Fuling Gas Field,Sichuan Basin

随着涪陵页岩气田钻探项目的推进,不断揭示出区内海相页岩具有非均质性强、岩性复杂等特征。以涪陵气田主力气层五峰组—龙马溪组页岩为例,首先采用详细、准确的ECS(Elemental Capture Spectroscopy Sonde)特殊测井资料,开展页岩中硅质成分来源分析,根据ECS测井和岩石薄片资料,结合页岩硅质成分来源分析结果,建立页岩矿物组分三端元图版,准确划分出页岩岩相;再运用常规测井资料,总结不同页岩岩相的测井响应特征,选取对页岩岩相敏感的去铀伽马和密度测井曲线建立测井识别图版。结果表明:常规测井资料识别出的页岩岩相与ECS特殊测井资料识别结果一致,匹配程度较高。整体而言,当TOC质量分数≥2%时,涪陵气田五峰组—龙马溪组页岩硅质成分来源以生物成因为主;当TOC质量分数<2%时,硅质成分来源以陆源碎屑为主。涪陵气田主要发育硅质页岩、混合型硅质页岩、富黏土硅质页岩、富钙硅质页岩、混合页岩、富黏土-粉砂混合页岩、富黏土粉砂质页岩和富粉砂黏土质页岩等8种页岩岩相,其中,具有高硅质含量、高TOC含量的硅质页岩和混合型硅质页岩岩相为开发较有利页岩岩相。研究成果提高了页岩岩相分类的准确性和实用性,对页岩气资源的高效开发具有指导意义。

With the development of Fuling shale gas field production, the marine shale reservoirs in Fuling Gas Field show obvious heterogeneity and complex lithology. Based on the comprehensive and accurate ECS （Ele- mental Capture Spectroscopy Sonde） special well logging data of Wufeng-Longrnaxi Formation shale, the siliceous component sources were analyzed, and according to the ECS special well logging data and thin section, com- bined with the different sources of siliceous components, the ternary diagram of shale mineral component was estab-lished to accurately divide shale lithofacies. The log response characteristics of different shale lithofacies were analyzed by using conventional logging data, and uranium-free gamma ray and density logging which are sensi- tive to shale lithofacies were selected to establish shale lithofacies identification logging plate. The result shows that the shale facies identified by conventional logging data is in accordance with the recognition results by ECS special logging data. When the TOC mass fraction of Wufeng-Longmaxi Formation shale is greater than 2%, the source of siliceous components is dominated by biogenic factors, when the TOC mass fraction is less than 2%, the source is mainly terfigenous debris. Eight kinds of lithofacies of Wufeng-Longmaxi Formation shales were identified, including siliceous shale, mixed siliceous shale, clay-rich siliceous shale, carbonate-rich siliceous shale, mixed shale, argillaceous-silty mixed shale, clay-rich silty shale and silty-rich argillaceous shale. The most favorable shale lithofacies was defined as the siliceous shale and mixed siliceous shale with high siliceous content and high TOC content. The result could effectively improve the accuracy and practicability of shale litho- facies classification and it is significant for the efficient development of shale gas resources.