Chuan-Jie Ren, Yong-Liang Yang, Hong-Jun Zhang, Dao-Yi Zhu
CO 2 miscible flooding is a key method to improve oil recovery. However, under most petroleum reservoir conditions, CO 2 cannot achieve miscibility with crude oil. Therefore, reducing the minimum miscible pressure (MMP) between CO 2 and crude oil has become a critical objective. This study investigated MMP reduction and CO 2 displacement efficiency of miscibility-enhancing agent (MEA) using low-permeability artificial cores and reservoir oil samples from the Xinjiang Oilfield. A core displacement method was established to determine the MMP and, in parallel, to screen four candidate MEAs. Nuclear magnetic resonance (NMR) technology was employed to probe the pore-scale mechanisms by which MEAs reduce the MMP between crude oil and CO 2 . Results showed that, before adding an MEA, the baseline MMP of CO 2 –crude oil system was 21.38 MPa. Among the four MEAs, tributyl citrate (TC) exhibited the strongest effect, lowering the MMP by 1.61 MPa. TC concurrently improved CO 2 conformance efficiency in both large pores and small pores, improving oil recovery during CO 2 flooding. These results demonstrated that TC-enabled miscibility tuning offers a practical pathway to reduce MMP and improve CO 2 conformance in low-permeability reservoirs. It provided a foundation for pilot-scale conformance control implementation in the Xinjiang Oilfield and analogous CO 2 flooding reservoirs.