TY  - EJOU
AU  - Wang, Xiaoguang 
AU  - Liu, Dehua 
AU  - Liu, Zhenping 
AU  - Luo, Zhen 
AU  - Yang, Guihua 
AU  - Li, Zongfa 
AU  - Huang, Lijuan 

TI  - Effective Pore-Throat Sweep Limits and Microscopic Oil Mobilization during CO<sub>2</sub>-WAG Flooding in Low-Permeability Conglomerate Reservoirs
T2  - Fluid Dynamics \& Materials Processing

PY  - 
VL  - 
IS  - 
SN  - 1555-2578

AB  - 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.
KW  - CO<sub>2</sub>-WAG; conglomerate reservoirs; oil displacement efficiency; nuclear magnetic resonance; producing limit

DO  - 10.32604/fdmp.2026.079864