The Micro-Occurrence Mechanisms of Tight Oil: Fluid–Rock Interactions at Microscale Pores, Nanoscale Pores, and Mineral Surfaces

Dongwei Zhang, Meng Han, Qianshan Zhou (), Tianrui Ye, Yujie Zhou, Ji Chang and Xiaohui Lin
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Dongwei Zhang: Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
Meng Han: Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
Qianshan Zhou: Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Tianrui Ye: Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
Yujie Zhou: Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
Ji Chang: Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
Xiaohui Lin: Wuxi Research Institute of Petroleum Geology, Sinopec Petroleum Exploration and Production Research Institute, Wuxi 214126, China

Energies, 2023, vol. 16, issue 9, 1-26

Abstract: Understanding the micro-occurrence mechanism of tight oil has long been a daunting challenge in the exploration and development of unconventional resources. This article discusses the micro-occurrence mechanism of tight oil through continuous extraction by combining thin casting, fluorescent thin sections, environmental scanning electron microscope observations, physical property testing, and X-ray diffraction experiments. The results indicated that in the tight sandstone of the Chang 8 Formation in the Ordos Basin, the average tight oil content was 35.46% for microscale pores, 35.74% for nanoscale pores, and 28.79% for mineral surfaces. Six types of micro-occurrence states of tight oil were identified: emulsion, cluster, throat, star-like, isolation, and thin film forms. Although clay minerals and heavy components dominate the adsorption of tight oil on mineral surfaces, micro-occurrence is fundamentally an oil–rock interaction process. Hence, oil–rock interactions and occurrence states were combined in this study to identify tight oil’s micro-occurrence mechanism. The van der Waals forces of attraction between asphaltene molecules and a mineral surface play a critical role, and minerals with hydroxyl groups can also combine with carboxyl and hydroxyl groups present in tight oil. As a consequence of the adsorption of heavy components by minerals, tight oil components remain in microscale and nanoscale pores with a higher saturation, increased aromatic hydrocarbon content, and greater fluidity. The heterogeneity of the components due to adsorption influences the physical properties and mineralization framework of tight oil reservoirs. These findings suggest that tight oil occurrence results from the coupling of microscopic occurrence and component heterogeneity in microscale and nanoscale pores.

Keywords: tight oil; micro-occurrence; occurrence mechanism; Yanchang Formation; Ordos Basin (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: 2023
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