Influence of surface cleaning on the wettability of calcite/oil/brine systems

Contact angle (θ) is a measurement that characterizes the wettability of solid surfaces. Typically, contact angle measurements are conducted under one of the following conditions; cleaned rock surface, aged rock surface, or native (intact) rock surface. However, conventional cleaning agents such as toluene, acetone, heptane, and methanol may adsorb onto the rock surfaces and influence the wettability of the rock/oil/brine system. The effect of rock surface preparation using solvents prior to wettability assessments on rock/oil/brine systems is not systematically investigated. The influence of surface cleaning using solvents on the wettability of calcite/oil/brine systems was investigated. Calcite surface wettability was estimated via contact angle at high temperature (353 K) and pressures (0.1 to 50 MPa) before and after exposure to formation fluids and solvents. We have also conducted imaging and nanomechanical properties analyses of the rocks’ surfaces to investigate adsorption, change in surface chemistry and roughness, and mechanical properties of the rocks via Scanning Electron Microscopy (SEM), Scanning Probe Microscopy (SPM), nanoindentation, Fourier transform infrared spectroscopy (FTIR) and X-Ray Fluorescence (XRF) analysis before and after exposure. The results showed that these solvents get adsorb onto the rock surfaces and/or fail to completely remove the crude oil components from the rocks surfaces. Consequently, the wettability of the rock/oil/brine system is modified. Moreover, different contact angle values were observed for the same rock surface under different cleaning agents. Therefore, results from this study demonstrate that restoration of the initial rock wettability after fluids exposure was challenging as different rock surface cleaning prior to contact angle measurements results in different rock wettability.