Herein is discussed the physicochemical mechanisms occurring during wettability alteration in mixed wet rocks. Defined by the strength with which a petroleum fluid adheres to the surface of the reservoir rock formation, wettability is of a great interest for oil recovery. The present work presents the wettability alteration of light and heavy crudes in strongly wetted sandstone, by the means of contact angle measurement. The spreading was found to be not only dependent of the reservoir fluid properties but also of the saturation of core. Different multiphase flow patterns were observed from the crude oil migration through the pore throats of reservoir formation suggesting a change in the surface properties of the reservoir rock. Furthermore, reservoir water salinity and presence of meta-aqua ions were found to promote pore blocking which further altered surface tension, thence the wettability.
In a typical oil reservoir, wettability appears as a governing parameter as it accesses the irreducible water saturation in the reservoir. Furthermore, it suggests how easily a petroleum fluid is displaced and has tremendous impact on what fluid is primarily produced. Several definitions are attached to wettability may be found in the literature. However, it is commonly accepted that wettability expressed the tendency of one fluid to spread or adhere to a solid surface in the presence of other immiscible fluids (Morrow 1990; Strand, Standnes, and Austad 2003). The fluid with the highest affinity for the solid surface is called the wetting fluid, whereas the other is called non-wetting fluid.
In immiscible state in the reservoir, oil and brine formed with grain a mixed wet system (Salathiel 1973), whose equilibrium depends primarily on the surface tension between each pair (Tang and Morrow 1999). Each surface tension acts upon its respective interface and defines the angle θ at which the liquid contacts the surface as illustrated in Figure 1 (Glover 1998; Young 1805).