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<p>After long-term water flooding, high-permeability domains in heterogeneous reservoirs are typically characterized by high degrees of oil depletion and high water cut, whereas low-permeability domains retain high oil saturation and low water cut. This contrast further amplifies reservoir heterogeneity and makes it increasingly difficult for chemical flooding to enhance oil recovery (EOR) through balanced displacement. Here, we constructed an in situ emulsification system composed of an associating polymer, surfactant, and salt (APSS) for coupled profile control and oil displacement. The crude-oil emulsification behavior, microstructure and rheology of high-water-content emulsions, seepage characteristics in a 70% water-cut sand-packed plate model, and EOR performance in water-flooded parallel heterogeneous sand-pack models were systematically evaluated. A polyacrylamide/surfactant/salt system (PSS) with comparable apparent viscosity and oil–water interfacial tension was used as the control. The results show that APSS exhibits a distinctive water-cut-responsive emulsification behavior that requires the synergistic action of all three components. In the high-water-content range of 50–90%, APSS forms highly viscous emulsions, whereas under low-water-content conditions it either forms low-viscosity emulsions or does not emulsify. The viscosity of the stable, high-viscosity APSS emulsions is 5 ~ 20 times higher than that of the injected displacing fluid and the crude oil. By contrast, PSS forms only weakly stable emulsions over a narrower water-content range of 40 ~ 60%, with viscosities only 2 ~ 3 times higher than those of the displacing fluid or crude oil. Confocal laser scanning microscopy (CLSM) and rheological measurements of the APSS emulsion at 70% water content reveal the coexistence of spherical oil-in-water droplets and filamentous/strand-like aggregates, giving rise to a multilevel structure and gel-like rheological behavior. In three heterogeneous displacement models with permeability contrasts of 5 ~ 10, APSS not only emulsified and displaced oil efficiently in high-permeability zones while generating substantial flow resistance, but also redirected the displacing fluid toward low-permeability zones. The average total oil recoveries achieved by APSS were 92.2%, 46.2%, and 89.8%, which were markedly higher than the corresponding values for PSS (79.8%, 32.8%, and 32.7%). This water-cut-viscosity-responsive in situ emulsification system provides a new technical strategy and experimental basis for deep fluid diversion and enhanced oil recovery in high-water-cut heterogeneous reservoirs.</p>

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Water-cut responsive in-situ emulsification profile-control and displacement system: construction, characteristics and oil recovery in heterogeneous reservoirs

  • 期刊论文

  • 发表日期：

    2026年7月28日

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  • Guoyu Liu,
  • Yongjun Guo,
  • Qiang Fu,
  • Cheng Jin,
  • Wei Zhang,
  • Di Pu,
  • Xinmin Zhang,
  • Ruijie He,
  • Huili Zhang

摘要

After long-term water flooding, high-permeability domains in heterogeneous reservoirs are typically characterized by high degrees of oil depletion and high water cut, whereas low-permeability domains retain high oil saturation and low water cut. This contrast further amplifies reservoir heterogeneity and makes it increasingly difficult for chemical flooding to enhance oil recovery (EOR) through balanced displacement. Here, we constructed an in situ emulsification system composed of an associating polymer, surfactant, and salt (APSS) for coupled profile control and oil displacement. The crude-oil emulsification behavior, microstructure and rheology of high-water-content emulsions, seepage characteristics in a 70% water-cut sand-packed plate model, and EOR performance in water-flooded parallel heterogeneous sand-pack models were systematically evaluated. A polyacrylamide/surfactant/salt system (PSS) with comparable apparent viscosity and oil–water interfacial tension was used as the control. The results show that APSS exhibits a distinctive water-cut-responsive emulsification behavior that requires the synergistic action of all three components. In the high-water-content range of 50–90%, APSS forms highly viscous emulsions, whereas under low-water-content conditions it either forms low-viscosity emulsions or does not emulsify. The viscosity of the stable, high-viscosity APSS emulsions is 5 ~ 20 times higher than that of the injected displacing fluid and the crude oil. By contrast, PSS forms only weakly stable emulsions over a narrower water-content range of 40 ~ 60%, with viscosities only 2 ~ 3 times higher than those of the displacing fluid or crude oil. Confocal laser scanning microscopy (CLSM) and rheological measurements of the APSS emulsion at 70% water content reveal the coexistence of spherical oil-in-water droplets and filamentous/strand-like aggregates, giving rise to a multilevel structure and gel-like rheological behavior. In three heterogeneous displacement models with permeability contrasts of 5 ~ 10, APSS not only emulsified and displaced oil efficiently in high-permeability zones while generating substantial flow resistance, but also redirected the displacing fluid toward low-permeability zones. The average total oil recoveries achieved by APSS were 92.2%, 46.2%, and 89.8%, which were markedly higher than the corresponding values for PSS (79.8%, 32.8%, and 32.7%). This water-cut-viscosity-responsive in situ emulsification system provides a new technical strategy and experimental basis for deep fluid diversion and enhanced oil recovery in high-water-cut heterogeneous reservoirs.