Towards a Nanoscopic Understanding of Oil-sandstone Wettability - Implications for Enhanced Oil Recovery

Due to the continuous rise in the demand for oil across the globe and diminishing availability of conventional sources, low salinity enhanced oil recovery (EOR) operations are increasingly deployed to extend crude production. Reservoir-rock wettability controls the low salinity effect, and it has been shown to be influenced by the presence of clay minerals, polar compounds in the crude oil and the activity of divalent ions. Nevertheless, a detailed understanding of the fundamental chemical and physical controls on the wetting behavior of reservoirs at the pore scale is still lacking. We have used quartz crystals as a model mineral surface to gain a better insight on sandstone oil/water wettability. The effect of the surface roughness and pre-treatment (using model oil compounds, dodecane and decanoic acid) on wettability has been studied. In addition, adhesion of decanoic acid to quartz surfaces was studied with atomic force microscopy (AFM). The wettability regime in quartz crystals was examined by using contact angle measurements with an environmental scanning electron microscopy (ESEM). Two different degrees of quartz crystal roughness were used. This allowed us to study the influence of nano-roughness on wettability while keeping the surface chemistry constant. Surface roughness of quartz and films was determined using atomic force microscopy (AFM) The quartz surfaces were studied without treatment and after being aged in , dodecane (non polar model oil phase) and decanoic acid mixtures (polar oil phase). The effect of brines on wettability alteration was studied by using range of brine concentration between 0.01 M to 1 M of NaCl, CaCl2, MgCl2, and KCl. AFM was used to study the oil-aged quartz crystals after brine treatment with the goal of observing any residual organic molecules. Results from these investigations show that dodecane-aged quartz crystals are more water whereas those pre-treated with decanoic acid are more oil wet. In addition, crystal with higher roughness are also more oil wet, this result can be explained by the presence of more remnants of decanoic acid than on the flat crystals (as seen by AFM).Overall, results from our investigations will contribute to increase our understanding and prediction of, the wetting behavior of the model mineral surfaces during low salinity water flooding IOR/EOR.