昭通页岩气区块龙马溪组下段海相页岩气储层沉积微相与测井识别

四川盆地昭通页岩气藏发育在奥陶系五峰组志留系龙马溪组下段,为黑色、灰黑色泥页岩,主要形成于弱氧化强还原的海相深水陆棚沉积环境。根据海相页岩基本特征、沉积相类型与沉积环境,结合观察岩心、分析实验薄片、录井等资料,将五峰组龙马溪组下段深水陆棚沉积亚相进一步划分为砂泥质、灰泥质、硅泥质、泥质深水陆棚4种沉积微相类型。在此基础上,根据不同沉积微相其元素俘获测井及能谱测井响应特征差异,形成基于元素俘获与能谱测井的页岩气储层沉积微相识别与划分技术。应用该技术对Y9井进行沉积微相划分,结果与薄片鉴定、岩心观察结论相一致。区域连井相对比分析明确了富有机质深水硅泥质陆棚是昭通页岩气示范区五峰组龙马溪组页岩气藏勘探开发的有利相带。该技术对四川盆地海相页岩储层沉积微相划分及勘探有利相带优选有一定借鉴意义。

Sedimentary Micro-facies and Log Identification of Marine Shale Gas Reservoirs in the Lower Part of the Longmaxi Formation of Zhaotong Shale Gas Block

The Zhaotong shale gas demonstration area in Sichuan basin is a typical representative of marine large-scale shale gas reservoirs in China.The black,gray and black marine shale developed in the lower part of the Ordovician Wufeng Formation and the Silurian Long Maxi Formation,which was mainly formed by the weak oxidation-strong reduction deep water shelf depositional environment.According to the basic characteristics,sedimentary facies type and sedimentary environment of marine shale,as well as the observation of core,experimental thin section and logging data,the deep-water shelf of the lower part of the Wufeng Formation-Longmaxi Formation was further divided into 4 microfacies:deep-water sandy muddy shelf,deep-water plaster shelf,deep-water silty shelf,and deep-water mud shelf.On this basis,according to the difference response characteristics of element capture logging and energy spectrum logging for different sedimentary microfacies,the technology of sedimentary microfacies identification and division of shale gas reservoirs based on element capture and energy spectrum logging was formed.This technique has been used to divide the sedimentary microfacies of well Y9,and the results were consistent with thin section and the conclusion of core observation.Through the comparative analysis of multi-well facies in the study area,it was clear that the organic-rich deep-water siliceous-argillaceous shelf was the most favorable facies zone in the lower part of Longmaxi Formation in Zhaotong shale gas demonstration area.This technique has certain reference significance for the division of sedimentary microfacies and the optimization of favorable exploration facies belts in marine shale reservoirs of Sichuan basin.