Streaming and zeta potentials of basalt as a function of pressure, temperature, salinity, and pH

Abstract

The electric surface charge of basalt in contact with filing fluids (e.g. water and CO2) has broad range of applications in varied fields such as gas geological storage sites, geothermal systems, and hydrocarbon reservoirs. The surface charge at the interface between a solid surface (e.g. rock) and liquid (e.g. aqueous solution) can be quantified by the zeta potential, thus zeta potential measurement is a useful technique for interpreting wetting characteristics of rock-fluid systems. However, there is no data for zeta potentials of basaltic rocks in presence of aqueous solutions or how zeta potentials may be affected by pressure, temperature, salinity, or pH. Thus, streaming potential measurements were performed to determine the zeta potential of basaltic rocks in the presence of aqueous NaCl solution at pore pressures (1.72 MPa to 6.9 MPa), temperatures (298 K and 323 K), brine salinities (1 wt% NaCl to 3.5 wt% NaCl), and pH values (4 to 10). Also, the effects of mineralogy and CO2-presence (dead and live brines) on the zeta potential were evaluated. The results showed that the zeta potential remained constant versus pressure, while it increased (became less negative) with increasing temperature and salinity, and decreased (became more negative) with increasing pH. This study provides key fundamental data and thus improves fundamental understanding of basalt-water-CO2 interactions, thereby aiding in the improvement of various industrial applications, including gas geo-storage schemes and geothermal energy production.