InterPore2026

Thermodynamic Control of Wettability Evolution in High-Porosity Carbonate Rocks for CO₂ and Hydrogen Storage

19 May 2026, 15:05

1h 30m

Poster Presentation (MS05) Physics of multiphase flow in diverse porous media Poster

Speaker

Dr Branko Bijeljic (Imperial College London)

Description

Carbonate reservoirs often exhibit complex wettability states due to the combined influence of geological and subsurface conditions, including mineralogy, pressure, temperature, and organic impurities. Understanding reservoir wettability is essential because it governs pore-scale interfacial behavior, multiphase flow, and capillary trapping mechanisms relevant to subsurface CO₂ and hydrogen (H₂) storage. Most existing experimental studies have attempted to induce hydrophobic conditions in CO₂–brine-rock systems by treating low-porosity substrates such as quartz, calcite, or Indiana limestone with organic acids. While even small concentrations of organic acids can modify surface wettability, extending these approaches to highly porous and permeable rocks remains experimentally challenging due to limited adsorption and retention of organic acid. As a result, wettability evolution in realistic high-porosity carbonate rocks is still poorly understood.
In this study, we investigate the wettability evolution of Ketton limestone under varying thermodynamic conditions. Ketton limestone, a high-porosity and high-permeability carbonate, was selected as a representative storage formation analogue. Rock substrates were saturated with stearic acid dissolved in decane at a concentration of 0.016 M to induce controlled wettability alteration. Static contact angle measurements were conducted in a high-pressure, high-temperature cell using CO₂ as the non-wetting phase and NaCl brine as the wetting phase. Experiments were performed over pressures ranging from 10 to 20 MPa, temperatures between 25 and 70 °C, and brine salinities of 5 and 10 wt% NaCl, representing realistic subsurface storage conditions.
The results demonstrate a systematic and monotonic increase in contact angle with increasing temperature, pressure, and salinity. At a salinity of 5 wt% NaCl and a pressure of 10 MPa, contact angles increased from 72° at 25 °C to 80° at 50 °C, and further increased to 93° at 60 °C, indicating a transition from weakly water-wet to intermediate-wet conditions. Increasing pressure further enhanced wettability alteration; at temperatures of 50–60 °C, contact angles increased from approximately 100–109° at 15 MPa to 111–116° at 20 MPa. At 70 °C, the contact angle increased to 124°, approaching a strongly CO₂-wet condition. At constant pressure and temperature of 10 MPa and 60°C respectively, increasing salinity from 5 to 10 wt% NaCl results in an additional increase in contact angle of approximately 10°, highlighting the role of ionic strength in stabilizing organic surface films on carbonate minerals.
Compared to previous studies on quartz and low-porosity limestones, these results reveal a distinct wettability response in a highly porous and permeable carbonate rock, where wettability alteration is governed by the coupled effects of thermodynamic conditions and surface chemistry rather than acid concentration alone. The findings provide a quantitative framework for selecting optimum thermodynamic conditions such as pressure, temperature, and salinity to achieve target wettability states (weakly water-wet, intermediate-wet, and oil-wet). This forms the basis for subsequent core flooding and pore-scale imaging analysis, which improves the understanding of wettability control and gas trapping in realistic subsurface carbonate formations.