Pore Structure and Factors Controlling Shale Reservoir Quality: A Case Study of Chang 7 Formation in the Southern Ordos Basin, China

Qing Li, Xuelian You (), Jiangshan Li, Yuan Zhou, Hao Lu, Shenghe Wu, Dali Yue and Houmin Zhang
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Qing Li: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Xuelian You: School of Ocean Sciences, China University of Geosciences (Beijing), Beijing 100083, China
Jiangshan Li: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Yuan Zhou: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Hao Lu: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Shenghe Wu: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Dali Yue: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
Houmin Zhang: National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China

Energies, 2024, vol. 17, issue 5, 1-16

Abstract: The lithofacies types, pore structure differences, and main controlling factors on the shale reservoirs are vital problems that need to be addressed in the process of shale oil exploration and development. This study explores the Luohe oilfield in the southern Ordos Basin, which is composed of organic-rich shale in the Chang 7 member, to clarify the reservoir properties and analyze major factors affecting the reservoir quality. The shale reservoir can be divided into five lithofacies using ternary diagrams of TOC, argillaceous minerals, and siliceous minerals: high organic-rich siliceous shale (HOSS), high organic-rich argillaceous shale (HOAS), medium organic-rich siliceous shale (MOSS), medium organic-rich argillaceous shale (MOAS), and low organic-rich shale (LOS). The type of organic matter in the studied samples is mainly Type I kerogen and Type II kerogen, predominantly Type II 1 kerogen. The kerogen mostly lie within the mature zone in the study area. Various types of pores have been identified in the studied shale: intergranular pores, intragranular pores, intercrystalline pores, organic matter pores, and seams around organic matter. The pores are commonly nanoscale to micrometer in scale, with diameters ranging from 10 nm to several microns. The S 1 content in shale is positively correlated with the macropore content, indicating that macropores in shale are the main effective oil storage spaces and are important for oil-bearing reservoirs. There is a good positive relationship between the macropore volume of shale and the content of organic matter. Organic matter in the shale can be beneficial for generating organic matter pores, dissolution pores, and seams at organic matter edge, resulting in better physical properties of shale reservoirs. There is a negative relationship between the quartz/feldspar content and macropores content, indicating that quartz and feldspar are detrimental for the macropore volume development. The lithofacies type is one of the important factors controlling the macropore volume. MOAS and HOAS are favorable lithofacies for the development of macropores. The findings of this study can be utilized for hydrocarbon exploration and development in the lacustrine shale formation of the Ordos Basin and other similar basins.

Keywords: shale reservoir; pore structure; Yanchang formation; Ordos Basin; reservoir quality; controlling factor (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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