Analytical Investigations of the Specific Features of Filtration Processes in Formations at a Low Saturation of the Displaced Phase

An analysis of the properties of solutions of the Buckley–Leverett equations describing the process of flooding productive strata has been performed. It has been shown that, apart from the widely known result consisting in the formation of a saturation jump on the front edge of the region of formation fluid displacement, a significant role, in terms of practical use, belongs to the dynamics of formation fluid displacement in the vicinity of the back edge of the displacement region, playing a major part at the late stage of deposits′ development when the saturation of the phase displaced from the formation tends to zero. It has been established that in the case of oil being a wetting phase, i.e. in developing hydrophobic oil reservoirs and also at the late stage of reservoirs’ development with a mixed type of wettability, within the framework of the Buckley–Leverett theory, the back edge of the displacement region remains immobile, in practice, and the maximum level of completeness in oil displacement from the formation does not occur. It has been shown that accounting for the action of capillary forces in modeling filtration processes ensures the mobility of the back edge of the displacement region and, accordingly, complete oil displacement from the formation.