Quantitative Evaluation of Shale-Oil Recovery during CO<sub>2</sub> Huff-n-Puff at Different Pore Scales
Yuan Gao, Qi Li, Xiaoming He, Haitang Yu, Yong Wang
Abstract
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.