Quantitative Evaluation of Shale-Oil Recovery during CO2 Huff-n-Puff at Different Pore Scales

• Published in: Energy & fuels Vol. 35; no. 20; pp. 16607 - 16616
• Main Authors: Gao, Yuan, Li, Qi, He, Xiaoming, Yu, Haitang, Wang, Yong
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.10.2021
• Subjects: Fossil Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.1c02734

CO2 huff-n-puff is an effective technique used in shale-oil reservoirs for supplementing the formation energy and realizing efficient development. This study focuses on typical shale core samples and crude oil. The quantitative evaluation of CO2 huff-n-puff recovery in shale-oil reservoirs at different pore scales was performed using the nuclear magnetic resonance technology combined with a laboratory physical simulation experiment. The huff-n-puff pressure and soaking time were considered as control variables. The results indicate a positive correlation between the oil recovery at different pore scales in a shale-oil reservoir and the CO2 huff-n-puff pressure. The production degree for a smaller pore was larger in the range 0–12.0 MPa; further, the production degree for a larger pore gradually increased with the CO2 huff-n-puff pressure. The soaking time had a considerable effect on the oil recovery at different pore scales. For a long soaking time (120 h), the production degree of crude oil in a large pore increased with the CO2 huff-n-puff pressure. However, for a short soaking time (24 h), the low huff-n-puff pressure stage (0–12.0 MPa) was dominated by the production of crude oil at a small pore scale, while the high huff-n-puff pressure stage (16.0–20.0 MPa) was dominated by the production at a large pore scale.