Quantitative characterization of microscopic occurrence and mobility of oil in shale matrix pores: A case study of the Shahejie Formation in the Dongying Sag
LI Junqian, SONG Zhaojing, WANG Min, ZHANG Pengfei, CAI Jianchao
1 National Key Laboratory of Deep Oil and Gas, China University of Petroleum-East China, Qingdao 266580, China 2 School of Geosciences, China University of Petroleum-East China, Qingdao 266580, China 3 College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China 4 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum-Beijing, Beijing 102249, China
The microscopic occurrence and mobility of oil in shale matrix pores are the key factors that restrict the efficient exploitation of terrestrial shale oil. This paper carried out quantitative characterizations on the amount, proportion, distribution and mobility of oil with different states in shale matrix pores, and theoretically established a series of models evaluating adsorbed, free and mobile amounts, and oil-adsorbed proportion (i.e., adsorption ratio equation). A method based on saturation- centrifugation-nuclear magnetic resonance tests was established to evaluate the microscopic occurrence and mobility of pore oil. The aforementioned models and methods have been applied to the Shahejie Formation shale oil reservoir in the Dongying Sag, Jiyang Depression, Bohai Bay Basin, and revealed the microscopic occurrence and mobility of n-dodecane in shale matrix pores at 20 ℃ and atmospheric pressure. It is concluded that: (1) the amounts of adsorbed and free oil in organic-rich shales are generally higher than those in organic-bearing shales, and the ratio of adsorbed oil to free oil is mainly between 1 and 2. The storage spaces of adsorbed and free oil in different types of shales are obviously diverse. (2) The average density of adsorbed oil of organic-rich shale (0.8331 g/cm3) is slightly higher than that of organic-bearing shale (0.8067 g/cm3). The average thickness of adsorbed oil of organic-rich shale (1.7475 nm) is about 3 times that of organic-rich shale (0.5734 nm). It shows that the organic- rich shale has a stronger oil-rock interaction. (3) The minimum pore diameter of storing free oil (dmin) is equal to the product of the average thickness of adsorbed oil and the pore shape factor. The dmin of organic-rich shale is of 3.5~10.5 nm, and pores of mainly storing free oil (mass ratio >70%) have a diameter of about 100 nm. The dmin of organic-bearing shale varies from 1.1~3.4 nm, and pores of mainly storing free oil have a diameter of about 30 nm. (4) The mobility index of oil in organic-rich shale (mean 6.24 mg·g-1·MPa-1) is higher than that in organic-bearing shale (mean 5.20 mg·g-1·MPa-1), and pore oil has a better mobility when the ratio of adsorbed oil to free oil is about 1.5. (5) Based on the oil-rock interaction, the coupling relationship of the oiliness and storage space of shale with the mobility of shale oil are established, and the internal relation between them is described mathematically, which will lay a theoretical foundation for discovering high-quality shale oil reservoirs.
李俊乾, 宋兆京, 王民, 張鵬飛, 蔡建超. 頁巖基質(zhì)孔隙油微觀賦存及可動(dòng)性定量表征—以東營凹陷沙河街組為例. 石油科學(xué)通報(bào), 2024, 01: 1-20 LI Junqian, SONG Zhaojing, WANG Min, ZHANG Pengfei, CAI Jianchao. Quantitative characterization of microscopic occurrence and mobility of oil in shale matrix pores: A case study of the Shahejie Formation in the Dongying Sag. Petroleum Science Bulletin, 2024, 01: 1-20.
