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<p>The potential application of foam for conformance control in heterogeneous reservoirs is critically dependent on brine salinity, yet the underlying pore-scale mechanisms involving residual oil have remained unclear. This study provides a pore-scale analysis, using a two-layer heterogeneous micromodel, to unravel how salinity (5,000 vs. 35,000 ppm NaCl) governs the complex interplay between foam and in-situ generated emulsions using sodium dodecyl sulfate (SDS) surfactant. In the absence of oil, low-salinity conditions produced a homogeneous, fine-textured SDS foam with high stability, leading to improved sweep efficiency across both high- and low-permeability layers. High salinity, by compressing the electrical double layer, yielded a coarse, heterogeneous foam with reduced stability due to enhanced coalescence and Ostwald ripening. The presence of residual oil revealed a critical paradigm shift: ultimate performance is not dictated by foam stability alone. At high salinity, the formation of coarse, unstable oil-in-water emulsion droplets, a consequence of ionic shielding, proved decisive. These large droplets acted as dynamic diverting agents, synergizing with foam to create temporary blockages in high-permeability pore throats via the Jamin effect. This mechanism effectively diverted flow into the low-permeability zone, significantly improving conformance. In contrast, the fine, stable emulsions formed at low salinity failed to block high-permeability pathways and instead caused unintended blockages within the low-permeability layer itself. Consequently, high-salinity foam injection achieved a final oil recovery of 88.02%, a significant 9.20-percentage-point improvement over the 78.81% recovery at low salinity. &#xa0;These results provided the first direct pore-scale evidence that optimizing salinity can tune the balance between foam stability and in-situ emulsion generation to maximize conformance control. This insight is crucial for designing effective foam strategies for enhanced oil recovery and also gas-based storage in saline, heterogeneous formations.</p>

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Pore scale insights into salinity driven foam stability and conformance control in heterogeneous porous media

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月26日

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  • Amir Hossein Molaei,
  • Matin Shahin,
  • Mohammad Simjoo

摘要

The potential application of foam for conformance control in heterogeneous reservoirs is critically dependent on brine salinity, yet the underlying pore-scale mechanisms involving residual oil have remained unclear. This study provides a pore-scale analysis, using a two-layer heterogeneous micromodel, to unravel how salinity (5,000 vs. 35,000 ppm NaCl) governs the complex interplay between foam and in-situ generated emulsions using sodium dodecyl sulfate (SDS) surfactant. In the absence of oil, low-salinity conditions produced a homogeneous, fine-textured SDS foam with high stability, leading to improved sweep efficiency across both high- and low-permeability layers. High salinity, by compressing the electrical double layer, yielded a coarse, heterogeneous foam with reduced stability due to enhanced coalescence and Ostwald ripening. The presence of residual oil revealed a critical paradigm shift: ultimate performance is not dictated by foam stability alone. At high salinity, the formation of coarse, unstable oil-in-water emulsion droplets, a consequence of ionic shielding, proved decisive. These large droplets acted as dynamic diverting agents, synergizing with foam to create temporary blockages in high-permeability pore throats via the Jamin effect. This mechanism effectively diverted flow into the low-permeability zone, significantly improving conformance. In contrast, the fine, stable emulsions formed at low salinity failed to block high-permeability pathways and instead caused unintended blockages within the low-permeability layer itself. Consequently, high-salinity foam injection achieved a final oil recovery of 88.02%, a significant 9.20-percentage-point improvement over the 78.81% recovery at low salinity.  These results provided the first direct pore-scale evidence that optimizing salinity can tune the balance between foam stability and in-situ emulsion generation to maximize conformance control. This insight is crucial for designing effective foam strategies for enhanced oil recovery and also gas-based storage in saline, heterogeneous formations.