Occurrence State and Time-Shift Characteristics of Residual Oil in Low-Permeability Reservoirs After Long-Term Waterflooding in Changqing Oilfield

Yangnan Shangguan, Boying Li (), Chunning Gao, Junhong Jia, Yongqiang Zhang, Jinghua Wang and Tao Xu
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Yangnan Shangguan: Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi’an 710018, China
Boying Li: State Key Laboratory of Petroleum Resources and Prospecting, College of Petroleum Engineering, China University of Petroleum, Beijing 100100, China
Chunning Gao: Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi’an 710018, China
Junhong Jia: Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi’an 710018, China
Yongqiang Zhang: Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi’an 710018, China
Jinghua Wang: Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi’an 710018, China
Tao Xu: State Key Laboratory of Petroleum Resources and Prospecting, College of Petroleum Engineering, China University of Petroleum, Beijing 100100, China

Energies, 2025, vol. 18, issue 8, 1-15

Abstract: This study focuses on a low-permeability sandstone reservoir in the Changqing Oilfield, aiming to elucidate the formation mechanism and occurrence state of residual oil during late-stage waterflooding development, thereby providing theoretical guidance for refined residual oil recovery. By integrating scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and digital core analysis, the oil–water occurrence state and dynamic characteristics during waterflooding were systematically investigated. NMR was employed to determine fluid distribution within core pores, while CT scanning was utilized to construct a 3D digital core model, enabling the identification of microscopic residual oil displacement and occurrence states at different flooding stages. The oil displacement efficiency was further analyzed based on variations in oil–water distribution and occurrence states within the core. The results demonstrate that pore and throat size and connectivity are the primary factors governing reservoir permeability. After high-pore-volume (PV) waterflooding, microscopic residual oil predominantly exists as dispersed droplets, films, and small-scale clusters or columns. Although prolonged high-PV waterflooding effectively expands the sweep volume, localized displacement efficiency declines, and reservoir heterogeneity adversely affects sweep volume maintenance. The post-flooding residual oil characteristics are collectively determined by the core’s local connectivity, wettability, and pore–throat morphology. This research systematically analyzes the occurrence patterns and evolutionary trends of residual oil in low-permeability reservoirs during long-term waterflooding, providing critical theoretical insights and technical support for enhanced oil recovery and residual oil exploitation.

Keywords: digital core; pore structure; flow simulation; micro water–oil displacement; remaining oil distribution (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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