Effects of cleaning process using toluene and acetone on water-wet-quartz/CO₂ and oil-wet-quartz/CO₂ wettability

Acetone, toluene, and heptane have been perceived as the conventional cleaning agents for the preservation of original water-wet rock reservoir wettability, and for restoration of oil-wet core to its initial wetting condition, prior to measurement of contact angles of CO₂-brine-rock systems. However, these organic solvents could be adsorbed on rock surfaces, which modifies the wettability of the reservoir rock and thus triggers uncertainties of the CO₂ containment estimation. Presently, there is scarcity of data in literature on the impact of cleaning agents on the wettability of rock/CO₂/brine/systems and its attendant effect on CO₂ storage capacities. To provide insights on the impact of cleaning agents on CO₂ wettability of sandstone, water-wet and oil-wet quartz substrates were aged in acetone, toluene, and heptane, respectively. Advancing and receding contact angles of CO₂-brine-quartz systems were measured at a constant temperature (323 K) and varying pressures (5–20 MPa). Impact of cleaning the minerals surfaces with air plasma, N₂ and oven after cleaning with either toluene or acetone on CO₂ wettability was also assessed and compared. The results show that chemicals that are used quite often to clean mineral surfaces can alter the rock wettability. Significant alterations in wetting conditions were observed when oil wet-rock was cleaned with toluene and water-wet rock was cleaned with acetone. Our results suggest that to preserve the original wettability, we will need to use toluene to clean the water-wet rock and acetone to clean the oil-wet rock. Heptane is only suitable for wettability modification of the oil-wet cores and not for restoration of oil-wet core to its original reservoir wettability. The results confirm that air plasma is the only way to remove surface contamination and organic carbon from the quartz substrates. Cleaning minerals surfaces or rock samples by toluene, acetone and heptane without air plasma will lead to incorrect contact angle and bias wettability measuments.