During the development of low-permeability oil fields, high-pressure water injection is employed as a means of increasing reservoir pressure and enhancing oil recovery. This process features an interplay between pressure-driven flow and spontaneous imbibition, which exerts a pivotal influence on the distribution of oil and water. To describe the dynamics of this interplay, pore-scale visualization experiments and core flooding online nuclear magnetic resonance experiments were conducted in the present work. The results demonstrate that after water flooding, residual oil predominantly exists in clustered forms. Initially, during high-pressure water injection and the early stages of well shut-in, crude oil movement is driven primarily by pressure. As the process continues, however, a spontaneous imbibition mechanism driven by capillary forces becomes the predominant force, which results in the transformation of clustered residual oil into various mobilizable forms. This reorganization of residual oil is a migration pattern from smaller to larger pores, facilitated by spontaneous imbibition.


Fracturing and water flooding have been popular technologies to achieve the effective development of tight oil reservoirs in recent years. However, in the late stage of production, the oil recovery rate declines with a rapid increase in the water cut. Water huff-puff could improve reservoir energy; however, the displacement and imbibition in the micro-nano pore throat and fracture systems are complex processes with unclear characteristics and position. Therefore, it is urgent to study the coupling mechanisms of oil-water displacement and imbibition in tight oil reservoirs. In this work, based on the phase field method of COMSOL Multiphysics software, we establish a two-dimensional microscopic numerical simulation model of the pore-fracture system, and carry out displacement-imbibition simulation programs of different injection media (water and surfactant) and injection methods (displacement, displacement-imbibition). By comparing the saturations and pressure distributions of different simulation programs, we analyze the changes in the oil-water interface, and summarize the action conditions of counter-current imbibition and pore throat limit. Finally, reasonable development suggestions are proposed for tight oil reservoirs.