Abstract
Establishing an effective displacement system for conventional water flooding development in low-permeability reservoirs is difficult, with generally low liquid and oil production and a worse water flooding effect. Imbibition oil recovery technology has received increasing attention from oil development workers because of its simple operation, low cost, and good oil increase effect. To explore the method and mechanism to further improve the effect of imbibition oil recovery, we study the imbibition and oil recovery effect and its influencing factors in a low-permeability reservoir in the Dagang Oilfield based on evaluation indexes of the adhesion work reduction factor, ratio of capillary force to gravity NB–1, regression analysis of the recovery rate of imbibition, proportional relationship with spontaneous imbibition, and dynamic imbibition effect in crack rocks. Results show that reducing the interfacial tension of the surfactant on the imbibition process has a dual effect. The selection of the surfactant for fractured tight reservoirs should not excessively pursue ultralow interfacial tension, and it should consider the surface wettability environment favorable for imbibition to ensure that a sufficient driving force can be provided. In the initial imbibition stage, the capillary force is large, the velocity of water imbibition in pores is fast, and the oil recovery rate is high; the holding time of the imbibition process is important to imbibition recovery. With the increase in imbibition time, the capillary force weakens, and the imbibition speed decreases to zero. With the increase in injection volume, reservoir pressure, pressure holding time, and imbibition cycles, the oil recovery increases, but the amplification of oil recovery decreases. From the technical and economic viewpoints, the optimal slug size, throughput cycle, and pressure holding time of the target reservoir are recommended as follows: 0.5 PV,three3 rounds, and greater than 96 h, respectively.
Highlights
With the rapid growth of global oil demand, the proportion of low-permeability oilfield reserves in proven recoverable reserves has been increasing day by day, but lowcost and efficient exploitation of such reservoirs have gradually become a problem of increasing concern for petroleum scientists and technicians.[1−5] To meet the development needs of similar reservoirs, petroleum scientists and technologists have put forward measures to improve the development effect, such as cyclic water injection,[6,7] acid fracturing,[8,9] and imbibition oil recovery,[10,11] based on the geological characteristics and water drive mechanism of low-permeability oilfields
Imbibition oil recovery technology has received considerable attention because of its simple operation, low cost, and good oil increase effect.[12−15] Since the 1950s, many studies have been performed on the mechanism and the law of imbibition and displacement of wetted phase fluids through capillary force in porous media
The surfactant solution can effectively reduce the interfacial tension between water and oil and improve the wettability of the rock surface, improving the imbibition oil recovery
Summary
With the rapid growth of global oil demand, the proportion of low-permeability oilfield reserves in proven recoverable reserves has been increasing day by day, but lowcost and efficient exploitation of such reservoirs have gradually become a problem of increasing concern for petroleum scientists and technicians.[1−5] To meet the development needs of similar reservoirs, petroleum scientists and technologists have put forward measures to improve the development effect, such as cyclic water injection,[6,7] acid fracturing,[8,9] and imbibition oil recovery,[10,11] based on the geological characteristics and water drive mechanism of low-permeability oilfields.Among them, imbibition oil recovery technology has received considerable attention because of its simple operation, low cost, and good oil increase effect.[12−15] Since the 1950s, many studies have been performed on the mechanism and the law of imbibition and displacement of wetted phase fluids through capillary force in porous media. Et al.[22] completed the submergence imbibition experiments by the weighing method and capillary method, consistent with the bottom water rising test results. Dagang Oilfield has 412 million tons of proven geological reserves in a low-permeability reservoir of which 163 million tons have been put into development. This accounts for 39.6% of the total low-permeability geological reserve in which 249 million tons have not been put into
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