Study On The Law And Influence Factors Of Imbibition Height In Low Permeability Reservoir

China's low-permeability oil reservoirs are widely distributed and contain large amount of crude oil.The proportion of oil and gas production in low-permeability oil reservoirs has increased year by year.Because the low-permeability layer has the characteristics of small pore radius,complex pore throat and tortuous structure,it is difficult for traditional waterflood development to produce oil.Capillary pressure within the pores of low-permeability oil reservoirs can exert the effect of imbibition and can drive the wetting phase fluid to replace the crude oil in the pores,thereby effectively increasing the crude oil yield of the low permeability reservoir.The flow distance of wetting phase fluid under the action of capillary pressure is defined as imbibition height,which can be used as a criterion for evaluation the effect of imbibition.Therefore,it is of great significance to study imbibition height and its influence factors to increase the crude oil production of low permeability reservoirs.The imbibition height and its influence factors are studied from the aspects of laboratory experiment and capillary model.Firstly,core experiment is used to study the effects of imbibition time,interfacial tension,salinity,and core wettability on the distance of infiltration.Next,using the orthogonal test method quantitatively analyze the key factors of the imbibition height.Finally,a new type of curved capillary model is established.Based on the fractal theory,the mathematical expression of imbibition height and imbibition time is derived under consideration of imbibition resistance and tortuosity.Several results are obtained.Firstly,the best interfacial tension for the different formation conditions results in the maximum final imbibition height,and imbibition height increases with the increase of salinity as well as core wettability.Secondly,the degree of salinity influences the final imbibition height to a different extent in different wettability reservoirs.Increase in imbibition height is more than 200%when salinity is less than2500mg/L,and increase is less than 50%when salinity is 70000mg/L.Thirdly,the effect of salinity on the distance of the final imbibition height is much greater than that of wettability and interfacial tension,and the effect of interfacial tension and the effect of salinity on the rate of the imbibition height are much greater than that of wettability.Fourthly,the ratio of the first-stage imbibition height h to the number of physical properties of the reservoir and the imbibition fluid _cr^0.67?cos?is fixed within a certain range,which can be determined by pre-production tests.This empirical formula can be used to effectively predict the first-stage imbibition distance in different production conditions.