Interaction of oil components and clay minerals in reservoir sandstones

The terpane and sterane compositions indicate that the oil adsorbed onto the clay surfaces appears to be more representative of the initial oil charging the reservoir than do the oil inclusions. This phenomenon could possibly demonstrate that the first oil charge preferentially interacts with the clay minerals occurring in the pores and as coatings around the grains. Although the variation of biomarker parameters between the free and adsorbed oils could be ascribed to the compositional changes of oil charges during the filling process and/or the differential maturation behaviors of these two types of oils after oil filling, the fractionation of the ratios of αββ/(αββ + ααα) regular steranes and C27 diasteranes/C27 regular steranes between these two types of oils can be unambiguously ascribed to the selective adsorption effects by the polar components and the active clay surfaces during the interaction of oil phase and clay surfaces.