本文为国家科技重大专项课题（编号 2017ZX05036004）和中国石油化工股份有限公司技术开发项目（编号 P19017- 2）资助的成果
To find out the source and reservoir characteristics as well as favorable shale oil & gas enrichment intervals of the Daanzhai Member in northern Sichuan, fine characterization and contrastive studies of lithofacies, source and reservoir characteristics aimed at the four sublayers of the second section of the Daanzhai Member (hereinafter referred to as the J1da 2) were carried out. It was based on core observation and description, guided by theoretical methods and technologies such as petrology and mineralogy, organic geochemistry and shale reservoir characterization. Then favorable intervals of shale oil and gas enrichment in vertical section were selected, and further exploration recommendation was proposed. Results suggest that: ① two interlayers are developed in J1da 2, that is, (argillaceous) shell limestone and (argillaceous laminated) siltstone. Four shale lithofacies types are identified, including low- medium- TOC clayey shale, medium- TOC lamellar - thin shell shale, low- TOC (laminated) silty shale and low- TOC silty shell calcareous shale. The 2nd sublayer is mainly consisting of medium- TOC clayey shale lithofacies and medium- TOC lamellar shell shale lithofacies, with relatively few interlayers and good shale continuity. However, the 4th sublayer primarily contains medium- TOC lamellar shell shale lithofacies, interbedded with shell limestone interlayers in different scales. ② The organic macerals of J1da 2 shale are mainly vitrinite. Solid asphalts are more developed in the 2nd and 4th sublayers. From bottom to top, organic matter types have changed six times, which are Ⅲ- Ⅱ2- Ⅲ- Ⅱ2- Ⅱ1- Ⅱ2 in turn. For the hydrocarbon generation capacity of J1da 2 shale, the 2nd and 4th sublayers are relatively better than the others, and the 4th sublayer is slightly better than the 2nd sublayer. ③ Physical properties of J1da 2 shale are obviously better than that of interlayers. Due to better hydrocarbon generation capacity, organic pores of the 2nd and 4th sublayers are more developed and the gas contents are relatively higher. Hence, the matching relationships of source- reservoir- (oil) gas bearing of the two sublayers are better. According to comprehensive evaluation, lamellar shell shale lithofacies in the 4th sublayer of J1da 2 is regarded as the optimal shale oil and gas enrichment interval, followed by clayey shale lithofacies in the 2nd sublayer of J1da 2. ④ In view of the strong heterogeneity in deposition and unstable distribution of good oil and gas bearing intervals in J1da 2 of the study area, it is advised to focus on the differences of argillaceous, calcareous and silty sediments, strengthen the study of the spatiotemporal distribution patterns of lithofacies (combinations) based on sublayer as units; pay attention to the differences in preservation conditions and gas bearing properties, and enhance the research on the selection of oil and gas exploration areas and layers.
LIU Zhongbao, LI Qianwen, LIU Guangxiang, LI Peng, CHEN Feiran, HAO Jingyu, ZHANG Wentao.2023. Source and reservoir characteristics as well as optimization of favorable shale oil and gas enrichment intervals of the Daanzhai Member in northern Sichuan[J]. Acta Geologica Sinica,97(10):3421-3437.