Research On Imbibition Law Of Fractured Tight Sandstone Reservoir And Its Influencing Factors

Spontaneous imbibition is an important oil displacement method in fractured tight sandstone reservoirs.It is of great significance to clarify the influencing factors of spontaneous imbibition in tight reservoirs for the efficient development of tight sandstone reservoirs and enhancing oil recovery.In this paper,through carrying out imbibition experiments and constructing imbibition theoretical models,the mechanism of spontaneous imbibition of fractured tight reservoir and its influencing factors are studied.Firstly,combined with high pressure mercury injection and nuclear magnetic resonance,the complexity of core pore structure is quantitatively characterized based on the fractal theory.It is found that the pore throat of tight sandstone is mainly in micrometer and submicron scale,and the physical meaning of fractal dimension obtained by different fractal models is different.The fractal model which is most suitable for characterizing the distribution characteristics of pore throat of tight sandstone is optimized,and the fractal dimension calculated has a good correlation with the core physical properties.Secondly,based on the capillary bundle model,the mathematical model of core matrix imbibition is constructed and the influencing factors of imbibition are studied.The results showed that core imbibition was affected by core pore throat structure,oil-water interfacial tension,wettability and other factors.The indoor matrix imbibition experiments of tight sandstones show that surfactants can increase the efficiency of core displacement through changing the core's wettability and reducing the adsorption of oil droplets on the core surface.Finally,the mechanical analysis of the spontaneous imbibition process of oil-water two-phase in fractures was carried out.Considering the buoyancy and gravity of the fluid,a mathematical model of spontaneous imbibition in fractures is derived based on Newton's second law,and its influencing factors are analyzed.The results show that the fracture imbibition rate decreases with increasing fracture length.As the fracture aperture increases,the influence on the imbibition of the buoyancy and gravity increase.The results of imbibition experiments on tight sandstones with fractures show that the core imbibition rate increases with the increase of the number of fractures.As the percolation channels for oil droplets,fractures can improve the efficiency of core displacement by reducing the adsorption of oil droplets on the surface of the core.