Characterization Of Remaining Oil Occurrence State And Potential Tapping Of A Type Of Reservoir After Polymer Flooding

In recent years,many scholars have discovered that there is still a large amount of remaining oil in the formation after polymer flooding,and it is more difficult to tap the remaining oil.Therefore,clarifying the occurrence state of the microscopic remaining oil distribution and quantitatively characterizing the oil saturation of various types of remaining oil can be of great significance to the improvement of oilfield recovery efficiency.Nowadays,the use of traditional laboratory experiments to obtain results has the disadvantages of long time,high cost,poor repeatability,etc.Therefore,the use of digital pore models to simulate the polymer flooding process to obtain a quantitative characterization of microscopic remaining oil after polymer flooding in a type of reservoir can be an oil field Improved oil recovery provides favorable support.In this paper,the real core pore structure is taken as the research object.First,CT scanning technology is used to determine the coordination number distribution frequency,find the coordination number interval with the highest distribution frequency,and set the maximum value.According to the constant velocity mercury injection,the pore throat size distribution result of the rock is obtained.Factors such as form factor and wettability are also considered.At the same time,an important method is used in the construction of the digital pore model,namely,adaptive porosity.Taking the above conditions into consideration,a digital pore model is constructed.Applying the principles of fluid mechanics and seepage mechanics,considering the polymer solution concentration,relative molecular mass,elasticity and interfacial tension and other polymer solution injection factors,the mathematical model of the saturated oil process,the mathematical model of the water flooding process,and the polymer flooding are established.Mathematical model of oil process.The corresponding simulation process is carried out through the established mathematical model,and the simulated recovery results of polymer flooding based on the mathematical model are compared with the physical simulation experimental recovery results to verify the rationality of the established pore model.Based on this,the study of a type of reservoir pore structure parameters and polymer solution injection parameters to quantitatively characterize the microscopic remaining oil after polymer flooding and the potential tapping of remaining oil.The research results show that the digital pore model constructed in this paper matches the rock structure of the reservoir.Compare the oil saturation of various remaining oils analyzed by fluorescence with the oil saturation of various remaining oils calculated based on the pore model to quantitatively characterize the occurrence status of various types of remaining oil,and divide the microscopic remaining oil types into membranes There are four types of remaining oil,namely,rectangular,corner-shaped,throat-shaped and cluster-shaped remaining oil.When the coordination number is greater,the number of oil in the pore throat is less,and the ratio of pore throat oil saturation is smaller.The clustered and film-like remaining oil in the pore model decreases the degree of oil saturation and the probability of forming remaining oil is smaller.,The higher the recovery rate of polymer flooding.When the pore-throat ratio in the pore model is smaller,the number of oil-bearing pores in the pore-throat is smaller,and the ratio of pore-throat oil-bearing saturation is smaller,the probability of forming remaining oil is smaller,and the recovery rate of polymer flooding is higher.The film-like remaining oil contains oil.The saturation and the oil saturation of the remaining oil in clusters are reduced.The other two remaining oil saturations did not change much.When the shape factor of the pore model is larger,the number of oil contained in the pore throat is smaller,the ratio of pore throat oil saturation is smaller,the recovery factor of polymer flooding is larger,and the oil saturation of the remaining oil in membrane and corner cubes decreases.With the increase of polymer solution concentration,relative molecular weight and relaxation time,and the decrease of interfacial tension,the less oil content in the pore throat,the smaller the oil content of the pore throat,and the higher the recovery rate of polymer flooding.Two remaining oil tapping methods are implemented after polymer flooding.One is to increase the concentration of the polymer solution.In the pore model,the oil saturation of the clustered remaining oil is greatly reduced.This is due to the increase in the viscosity concentration of the polymer solution and the spreading range Increase the driving force,make the remaining oil in clusters migrate and improve the oil displacement efficiency.Another method to reduce the interfacial tension will reduce the capillary resistance and reduce the starting pressure of the remaining oil in the cluster and the remaining oil in the throat,which is mainly controlled by the capillary force.It has a certain effect on further tapping the remaining oil potential.