Wettability Contrasts in Kaolinite and Illite Clays : Characterization by Infrared and X-ray Absorption Spectroscopies

A reservoir rock is a porous geological formation in contact with two liquids : brine and oil. An improved knowledge of rock wettability is of primary importance to estimate the amount of crude oil in underground resources. The petroleum industries have observed that wettability contrasts in sedimentary reservoir rocks are largely correlated to the presence of clays (illite andlor kaolinite) in the rock's intergranular space. More precisely, the grain surfaces of illite show a preference to brine. Kaolinite preferentially adsorbs oil, which imparts its hydrophobic characteristics to the mineral surface. Using X-ray absorption and Fourier Transform Infrared spectroscopies, we studied at the atomic level the adsorption process of asphaltenes in the presence of water. We show experimentally that the wettability contrasts obberved in kaolinite and illite are related to structural differences between these two clays and we show the primordial role of the grain surface hydroxyls. At last, the role of the water in the asphaltenes adsorption process has been investigated, using the same spectroscopies.