Impact of pressure, temperature, and salinity on helium-quartz wettability.

Helium (He), widely used in cryogenic and superconductivity technologies, occurs naturally in subsurface reservoirs, where its migration, trapping, and retention are governed by wettability. Although clean quartz is initially strongly water-wet and He is inert and non-polar, and has negligible adsorption tendency, contact angle can still vary with pressure, temperature, and brine salinity through changes in the gas-brine-solid interfacial energy balance. Yet systematic wettability data for He-rock systems remain scarce, limiting reliable assessment of its subsurface behaviour. To address this gap, we present the first comprehensive experimental dataset of He-quartz-brine contact angles, as well as He-brine interfacial tension values, measured using tilted plate method under reservoir-relevant conditions, including pressures of 0.1-20.0 MPa, temperatures of 303-333 K, and brine salinities of 0.0-0.3 m (0-17,430 ppm) NaCl. Next, using 36 experimental data points, empirical correlations were developed to relate advancing and receding contact angles to pressure, temperature and salinity, while a complementary density-based relationship forecasted contact angle with higher accuracy. Lastly, the trends and governing mechanisms were compared with published wettability data for more reactive gases including CO2 and H2. The results demonstrated that He remains strongly brine-wet across all conditions, with advancing and receding angles of 12-44° and 8-38°, respectively. Additionally, contact angles increase systematically with pressure, temperature, and salinity, with salinity exerting the dominant control (increase of 16-25° as the brine salinity increased from 0.0 to 0.3 m NaCl) through electrical double layer thickness reduction. Importantly, despite these systematic variations, the Helium-quartz-brine system remained consistently brine-wet across all tested conditions. These findings established a quantitative framework for evaluating He contact angle in quartz-rich reservoirs, with potential implications for subsurface gas storage systems involving CO2 and H2.