Separation and Chemical Characterization of Wetting Crude Oil Compounds

To improve the understanding of wettability, especially the influence of colloidal stability and composition of crude oil, wetting experiments on quartz sand were performed with an asphaltene-rich oil, a resin-rich oil, and with model oils containing different colloid compositions. A two-step procedure was developed to investigate the wetting behavior. In the first step those crude oil components were extracted, which preferentially wet solid surfaces. The extracted crude oil components were characterized in the second step. The amount of adsorbed oil components correlates with the stability of the crude oil colloids: low colloidal stability of crude oil leads to larger amounts of adsorbed components than does high colloidal stability. The addition of resins and/or low molecular weight asphaltenes to the crude oil stabilizes the crude oil colloids; i.e., a lower amount of wetting components are isolated by extraction in such systems. To find out, which fraction of the adsorbed oil components determines the wetting behavior of a crude oil, the wetting properties of the toluene solutions of these fractions were compared to those of the toluene solutions of the precipitated crude oil colloids. The fractions extracted with the solvent systems chloroform and methanol/chloroform showed nearly the same wetting behavior as the crude oil colloids. These fractions are characterized by the highest molecular weights, higher sulfur compositions, and the lowest H/C ratios. On the other hand, the nitrogen compounds predominate in the acetone fraction.