Experimental study of enhanced oil recovery by CO 2 huff-n-puff in shales and tight sandstones with fractures
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ORIGINAL PAPER
Experimental study of enhanced oil recovery by CO2 huff‑n‑puff in shales and tight sandstones with fractures Chao‑Fan Zhu1,2 · Wei Guo1 · You‑Ping Wang3 · Ya‑Jun Li2 · Hou‑Jian Gong2 · Long Xu2 · Ming‑Zhe Dong2,4 Received: 11 August 2020 / Accepted: 12 November 2020 © The Author(s) 2020
Abstract The fractures and kerogen, which generally exist in the shale, are significant to the CO2 huff-n-puff in the shale reservoir. It is important to study the effects of fractures and kerogen on oil recovery during C O2 huff-n-puff operations in the fracture– matrix system. In this study, a modified C O2 huff-n-puff experiment method is developed to estimate the recovery factors and the CO2 injectivity in the fractured organic-rich shales and tight sandstones. The effects of rock properties, injection pressure, and injection time on the recovery factors and CO2 usage efficiency in shales and sandstones are discussed, respectively. The results show that although the C O2 injectivity in the shale is higher than that in the sandstone with the same porosity; besides, the recovery factors of two shale samples are much lower than that of two sandstone samples. This demonstrates that compared with the tight sandstone, more cycles are needed for the shale to reach a higher recovery factor. Furthermore, there are optimal injection pressures (close to the minimum miscible pressure) and CO2 injection volumes for C O2 huff-npuff in the shale. Since the optimal CO2 injection volume in the shale is higher than that in the sandstone, more injection time is needed to enhance the oil recovery in the shale. There is a reference sense for CO2 huff-n-puff in the fractured shale oil reservoir for enhanced oil recovery (EOR) purposes. Keywords Shale · Tight sandstone · CO2 huff-n-puff · Fracture · Injectivity of CO2
1 Introduction In recent years, the majority of newly discovered oil reservoirs are unconventional reservoirs. Shale oil reservoirs have been discovered in the Bakken Formation (3.65 billion barrels), Three Forks (3.73 billion barrels), Appalachian, Gulf of Mexico, west Siberian, Songliao, and Ordos basins around the world (Gaswirth and Marra 2015). There is a strong consensus that oil can be produced from certain Edited by Yan-Hua Sun * Ming‑Zhe Dong [email protected] 1
College of Construction Engineering, Jilin University, Changchun 130026, Jilin, China
2
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
3
Petroleum Exploration and Production Research Institute, Sinopec, Beijing 100083, China
4
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
fractured shale oil reservoirs (Zou and Yang 2013). Similar to the tight sandstone, the shale has very pore storage and permeable property, which is adverse to the production (Bustin and Bustin 2012; McGlade et al. 2013). Besides, because shales are rich in kerogen (Wang et al. 2019), the oil in shale consists of free, adsorbed, and dissolv
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