Effect of capillary number on the residual oil saturation during chemical flooding

The paper presents experimental results of studying capillary displacement curves in chemical methods of enhancing oil recovery. The analysis of the theory of capillary number and changes in this parameter in chemical methods of enhancing oil recovery is carried out. The results of studies of capillary displacement curves are analyzed, and general patterns and features of the behavior of these curves in various experimental conditions are revealed. The analysis showed that with a change in formation wettability, porosity, permeability, and pore structure, the capillary displacement curves change. Under changing formation conditions, classical capillary displacement curves previously obtained in the course of basic experiments do not allow predicting residual oil saturation, and in addition, the maximum oil recovery does not correspond to the maximum values of capillary numbers. In the practice of oil field development, there is no need to use high concentrations of surfactants to reduce the surface tension to an ultra-low level. Addition of polymer, and alkali (in appropriate concentration) provides high oil recovery due to interaction of surfactants, polymer and alkali. Currently, in China, ASP flooding technology (alkaline-surfactant-polymer flooding – alkaline flooding and combined use of alkali, surfactant, and polymer) is the most effective method of enhancing oil recovery in flooded oil fields and gives good results. Therefore, it is necessary to study the micromechanisms of residual oil mobility and filtration. Studies of the capillary displacement curve, considering the structure of the reservoir and its basic filtration characteristics, are of decisive importance in the development of oil fields in China, and these curves can also be used in world practice as a basis for enhancing oil recovery.