CO2/brine interfacial tension and rock wettability at reservoir conditions: A critical review of previous studies and case study of black shale from Malaysian formation

In this study, previous literature that discussed CO2/brine interfacial tension and wettability of rock/CO2/brine systems were critically reviewed. Using a shale core from Malaysian formation, laboratory experiments were conducted to extend the scope of available data for CO2/brine interfacial tension (IFT) and contact angles of shale/CO2/brine system, as well as shale/oil/brine system to elevated pressures (8 MPa-22 MPa), temperatures (80 degrees C-180 degrees C), and NaCl concentrations (0 wt% - 7 wt %), that are representative of downhole conditions. HPHT (high pressure, high temperature) drop shape analyzer (DSA100) instrument was employed for the contact angles and IFT measurements. The CO2/brine IFT was measured using the pendant drop method while the sessile drop/captive bubble techniques were used to measure the advancing and receding contact angles respectively. Correlations were developed for predicting changes in contact angles and CO2/brine IFT as a function of changing temperature, pressure and salinity. Results showed that the crude oil advancing and receding contact angles for shale/oil/brine system decreased with increasing temperature and salinity, but slightly increased with pressure. The brine advancing and receding contact angles of shale/CO2/brine system increased with increasing pressure and salinity, but decreased with increasing temperature. Conversely, the CO2/brine IFT increased with increasing temperature and salinity, but decreased with increasing pressure. The simulated and experimental values showed reasonable consistency with R-2 values of 98% and 99% gotten from the statistical fits of the contact angles values. Precisely, at 80 degrees C and 7 wt% NaCl concentration, the shale surface became strongly CO2-wet, with brine advancing contact angles of 139.92 degrees, 156.06 degrees, and 162.63 degrees when the pressure reached 18 MPa, 20 MPa, and 22 MPa respectively. At similar salinity conditions and 10 MPa, significant increment in CO2/brine IFT from 36.50 mN/m to 47.54 mN/m occurred with increasing temperature from 80 degrees C to 180 degrees C. Such wettability modification of the rock surface and change in IFT at elevated temperature, pressure and salinity will greatly influence hydrocarbon recovery, as well as CO2 containment security in Malaysian unconventional shale formation.