Open Access

ARTICLE

Effective Pore-Throat Sweep Limits and Microscopic Oil Mobilization during CO₂-WAG Flooding in Low-Permeability Conglomerate Reservoirs

Xiaoguang Wang^1,2, Dehua Liu^1,2,*, Zhenping Liu³, Zhen Luo³, Guihua Yang^1,2, Zongfa Li^1,2, Lijuan Huang^1,2,*

1 State Key Laboratory of Low Carbon Catalysis and Carbon Dioxide Utilization (Yangtze University), Wuhan, China
2 School of Petroleum Engineering, Yangtze University, Wuhan, China
3 Research Institute of Exploration and Development, Xinjiang Oilfield Company, PetroChina, Karamay, China

* Corresponding Authors: Dehua Liu. Email: ; Lijuan Huang. Email:

(This article belongs to the Special Issue: Complex Flows in Geological and Surface Processes)

Fluid Dynamics & Materials Processing 2026, 22(7), 2 https://doi.org/10.32604/fdmp.2026.079864

Received 29 January 2026; Accepted 11 June 2026; Issue published 31 July 2026

Abstract

Low-permeability conglomerate reservoirs are characterized by complex pore structures and poor sweep efficiency, making the optimization of carbon dioxide-water alternating gas (CO₂-WAG) injection critical for enhanced oil recovery. To evaluate the displacement performance of CO₂-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 CO₂ flooding and CO₂-WAG schemes with varying cycle numbers and gas-water ratios (GWRs) were systematically compared. In situ online nuclear magnetic resonance (NMR) monitoring was employed to quantitatively characterize the mobilization of microscopic remaining oil during flooding. The results demonstrate that CO₂-WAG significantly outperforms continuous CO₂ 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 CO₂ 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, CO₂-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 CO₂ 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.

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Keywords

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