Maximising CO2 sequestration efficiency in deep saline aquifers through in-situ generation of CO2-in-brine foam incorporating novel CO2-soluble non-ionic surfactants

The geological sequestration of carbon dioxide (CO 2 ) within deep saline aquifers remains a critical pathway for achieving long-term climate stabilisation and net-zero targets. This study presents a novel strategy to augment both the efficiency and security of CO 2 storage through the in-situ formation of CO 2 -in-brine foams facilitated by non-ionic CO 2 -soluble propoxylated-ethoxylated alcohols surfactants, specifically 2EH-PO 5 -EO 9 and 2EH-PO 5 -EO 15 . A comprehensive suite of laboratory investigations was conducted under representative reservoir conditions (70 °C and 3200 psi), including cloud point pressure analysis, foam stability monitoring, interfacial tension (IFT) reduction, wettability alteration studies, CO 2 solubility measurements, and core flooding experiments. The results reveal that both surfactants exhibit strong solubility in supercritical CO 2 and brine, enabling stable foam generation without degradation. Among them, 2EH-PO 5 -EO 15 demonstrated superior performance, achieving a marked reduction in CO 2 –brine IFT, from 32 to 6.7 dyne/cm, and enhancing CO 2 solubility in brine by over 100 % (from 1.25 to 2.51 mol%) compared to pure CO 2 scenario; thus strengthening solubility trapping. In parallel, wettability characterisation showed a transformation of the sandstone substrate from strongly water-wet (θ ≈ 18°) to an intermediate gas-wet condition (θ ≈ 71°), significantly amplifying the potential for residual trapping. Core flooding assessments corroborated these synergistic effects, demonstrating reduced CO 2 mobility and improved sweep efficiency through foam stabilisation and rock–fluid interfacial modification. Altogether, this work underscores the efficacy of CO 2 -soluble non-ionic surfactants in enhancing storage security and injectivity, offering a technically and economically attractive approach to large-scale CO 2 sequestration in saline aquifers. Also, the current results establish a strong foundation for advancing toward field-scale implementation and represent a significant step forward in creating sustainable solutions for carbon management. • Improving CO 2 sequestration in the saline aquifers via generation of in-situ foam. • The application of novel non-ionic CO 2 -soluble propoxylated-ethoxylated alcohols surfactants. • CO 2 -soluble surfactants exhibit strong solubility in supercritical CO 2 and brine, enabling stable foam generation without degradation. • The strengthening CO 2 solubility trapping ocuured due to enhancing CO 2 solubility in brine and IFT reduction. • The wettability alteration to an intermediate gas-wet amplifying the potential for residual trapping.