Experimental And Simulation Study On Remaining Oil Distribution In Ultra High Water Cut Stage Based On CT

China’s dependence on importing oil has exceeded 70%,and energy security has become an important topic affecting national security.There are two ways to reduce the dependence on importing oil,one is to expand the exploration of oil and gas fields,and the other is to increase crude oil production.The old oilfields in eastern China have gradually entered the late development stage,and most of the oilfields have entered high water cut or even ultra-high water cut stage.Research shows that most of the crude oil is still produced in the period of ultra-high water cut.Therefore,it is of great significance to clarify the oil-water distribution,and the remaining oil initiation mechanism in the period of ultra-high water cut,in order to improve China’s crude oil recovery and ensure China’s energy security.In this study,the remaining oil distribution in ultra-high water cut stage was studied by means of experiment and simulation.With the help of CT scanning technology and digital rock,the influence of pore size,rhythm and homogeneity on remaining oil distribution in ultra-high water cut stage is studied.Then the quantitative analysis of remaining oil clusters in different displacement stages is carried out,and drawn the different types of remaining oil clusters evolution law.According to the characteristics of oil-water distribution in ultra-high water cut stage,the follow-up displacement experiment in ultra-high water cut stage is carried out,and then studied the influence of follow-up displacement on remaining oil production.At the same time,N-S equation and phase field method was used to simulate the displacement process in rhythm and random porous media model.The effects of displacement pressure difference,wettability,viscosity ratio,injection speed and surface tension on oil-water distribution are discussed.The remaining oil production under different conditions is compared and studied,and the remaining oil production methods of different models are given.The results show that the core with larger pore size is easier to form large connected network-like remaining oil,and the remaining oil in small pore size core distribute more dispersed.It can enhance oil recovery by improving washing efficiency for the core with larger pore size and improving sweep efficiency for the small pore size core when entered the ultrahigh water cut stage.In rhythmic cores,the displacement efficiency of the remaining oil in the pores with smaller particles is relatively higher,and the remaining oil in the pores with larger particles mainly occurrence in the form of connectivity.And the displacement efficiency of rhythmic core can be effectively by improving the injection speed.Heterogeneity of the core has a great influence on the remaining oil distribution,and the remaining oil distribute more dispersed in the heterogeneous core.Continuous water injection has limited effect on enhancing oil recovery after the heterogeneous core entering the ultra-high water cut stage.The simulation results show that enhanced displacement pressure difference can effectively enhance oil recovery,rhythmic structure can also affect the remaining oil distribution,and the recovery rate in reverse rhythm model is relatively high.And results also shows that recovery rate can be higher when the wettability is wetter,the viscosity ratio is higher,and the surface tension is lower.By means of PLS regression,the correlation between recovery rate and surface tension and water-oil viscosity ratio is relatively higher,it’s effective to initiate the remaining oil when the surface tension is lower down and the water-oil viscosity ratio is increased.