Study On Characteristics And Laws Of Imbibition After Tight Oil Reservoir Layers

Tight reservoirs have the characteristics of low porosity,low permeability,and poor pore connectivity.Large-scale hydraulic fracturing is usually required to form a complex fracture network.After fracturing,a large amount of fracturing fluid will stay in the formation during the stuffy well stage.The whole process of fracturing and stuffy well is accompanied by imbibition between fracturing fluid and reservoir matrix.Therefore,studying the imbibition characteristics and laws of tight reservoirs is very important for reservoir development and production increase.In this paper,the influence of factors and characteristics of tight reservoirs on the process of imbibition is studied,and the correlation analysis of the factors is carried out through orthogonal experiment analysis method,and the following understandings are obtained:(1)Consider the drop zone due to imbibition liquid level in the indoor imbibition experiment Based on the buoyancy change between the core and the balance,the mass recovery formula was revised.(2)In the process of imbibition,temperature affects the viscosity of crude oil,which in turn changes the oil-water interfacial tension and reduces the viscous resistance of crude oil.With the increase of temperature,the imbibition recovery factor gradually increases;pressure mainly affects the early stage of imbibition The imbibition rate mainly affects the pores of the reservoir.In the case of similar core physical properties,the smaller the permeability and the smaller the pores,the smaller the compressibility of the pores.Therefore,under low permeability conditions,the greater the permeability The smaller the pressure,the smaller the influence of the imbibition recovery rate.The permeability mainly corresponds to the capillary force,but the permeability is not as small as possible.There is a permeability limit on which the permeability is directly proportional to the imbibition recovery factor,and vice versa.Clay minerals mainly affect the connectivity of pores,and the expansion of clay minerals in contact with water damages the reservoir and affects permeability.(3)There are two driving forces for imbibition in the case of low permeability,one is capillary force as the leading force,and the other is ionic osmotic pressure as the driving force for imbibition.Accumulation experiments and formation conditions are carried out by considering the factors under laboratory conditions.The factor accumulation experiment is carried out,and it is concluded that the F value of permeability is the largest,and it has the highest correlation with the imbibition recovery factor.In addition,through acoustic wave theory,an indoor acoustic wave imbibition experiment was carried out.The experiment showed that the frequency of acoustic wave is directly proportional to the imbibition recovery factor,and the cavitation of acoustic wave will produce negative pressure and bubble generation in the pores of the crude oil-caused by the process of burst The viscosity of the crude oil changes,and the mechanical action of sound waves will cause the porous medium to absorb the sound wave energy,causing the temperature to rise.In addition,sound waves can damage the surface structure of the core,which in turn affects the permeability of the core.