@Article{fdmp.2026.079864,
AUTHOR = {Xiaoguang Wang, Dehua Liu, Zhenping Liu, Zhen Luo, Guihua Yang, Zongfa Li, Lijuan Huang},
TITLE = {Effective Pore-Throat Sweep Limits and Microscopic Oil Mobilization during CO<sub>2</sub>-WAG Flooding in Low-Permeability Conglomerate Reservoirs},
JOURNAL = {Fluid Dynamics \& Materials Processing},
VOLUME = {},
YEAR = {},
NUMBER = {},
PAGES = {{pages}},
URL = {http://www.techscience.com/fdmp/online/detail/27485},
ISSN = {1555-2578},
ABSTRACT = {Low-permeability conglomerate reservoirs are characterized by complex pore structures and poor sweep efficiency, making the optimization of carbon dioxide-water alternating gas (CO<sub>2</sub>-WAG) injection critical for enhanced oil recovery. To evaluate the displacement performance of CO<sub>2</sub>-WAG and determine the lower limit of effectively swept pore throats, this study presents long-core flooding experiments conducted on cores from the KS Formation of the B Oilfield in the Junggar Basin under reservoir conditions (20.1 MPa and 58°C). Continuous CO<sub>2</sub> flooding and CO<sub>2</sub>-WAG schemes with varying cycle numbers and gas-water ratios (GWRs) were systematically compared. <i>In situ</i> online nuclear magnetic resonance (NMR) monitoring was employed to quantitatively characterize the mobilization of microscopic remaining oil during flooding. The results demonstrate that CO<sub>2</sub>-WAG significantly outperforms continuous CO<sub>2</sub> flooding. Among the tested scenarios, three alternating cycles and a GWR of 1:1 yielded the highest oil displacement efficiencies of 64.8% and 66.13%, respectively, representing improvements of 23.6% and 24.53% over water flooding and 4.75% and 6.08% over continuous CO<sub>2</sub> flooding. NMR analysis revealed that water flooding primarily mobilizes crude oil in larger pore throats, with an effective sweep limit of approximately 18.2 nm. In contrast, CO<sub>2</sub>-WAG extends the lower limit of effectively swept pore throats to 9.52 nm, enabling the recovery of oil trapped within mesopores and micro/nano-scale pore systems. Mechanistically, the injected water slugs improve sweep efficiency and suppress gas channeling, while the CO<sub>2</sub> slugs reduce crude oil viscosity and enhance displacement within smaller pores. This synergistic combination of macroscopic sweep improvement and microscopic displacement enhancement substantially increases oil recovery.},
DOI = {10.32604/fdmp.2026.079864}
}