Study On The Influence Of Pore Structure Parameters On The Occurrence State Of Microscopic Remaining Oil

In recent years,a large number of studies have shown that even if enhanced oil recovery technologies such as polymer flooding and terpolymer flooding are adopted,there is still a large amount of remaining oil in rock reservoirs.However,natural rock reservoirs are porous media,and their internal pore space is complex,making it difficult to excavate remaining oil.Therefore,it is necessary to study the influence of pore structure parameters inside rocks on the occurrence of microscopic remaining oil.It is of great significance to further improve oil recovery.The reconstruction of pore structure in rock reservoir by digital core method can more accurately locate the occurrence position and status of remaining oil,and quantitatively characterize the microscopic remaining oil,which can provide favorable support for further exploitation of oil field.In this paper,the remaining oil in the pore structure is taken as the research object.Firstly,the indoor microscopic visualization experiment is used to carry out the microscopic oil displacement experiment of water flooding and post-polymer flooding.After the displacement,the remaining oil is divided into the following four types: cluster,column,film and blind end,and the quantitative analysis and pore characteristics analysis of their distribution are carried out.Then,in order to accurately describe the internal characteristics of pores,natural cores were selected to carry out indoor oil displacement experiments based on CT scanning,and two experimental schemes of water flooding and polymer flooding were designed.Avizo software was used to conduct image processing of CT data and three-dimensional reconstruction of pore structure,so as to truly restore the internal pore characteristics of cores,obtain accurate pore parameters,and characterize the pore structure.Including: pore radius,throat radius,pore-throat ratio,coordination number,shape factor.At the same time,the classification and identification of the microscopic remaining oil were carried out to study the utilization of the same block of remaining oil in the same position,and the results were consistent with those of the microscopic visualization experiment.Then,on this basis,the quantitative characterization of pore structure parameters on the occurrence state of microscopic remaining oil is studied.In this paper,the sample of X1-3 core is taken as an example to analyze the experimental results after water flooding and polymer flooding.Firstly,in Avizo software,the pore structure model with different pore-throat ratio,coordination number and shape factor was extracted,and its number was counted to calculate the oil content of pore and throat.The remaining oil stored in the pore is extracted separately,classified according to the above classification standard of the occurrence state of the remaining oil,and its pore and throat ID are located.Finally,COMSOL software was used to conduct numerical simulation of oil-water two phase flow based on different pore structure models by using slice data of CT scan.Compared with CT scan experiment,pore characteristics of pore-throat ratio,coordination number and shape factor were considered.The results show that with the decrease of pore-throat ratio,the increase of coordination number and shape factor,the probability of remaining oil formation is smaller,the number of oil in pore-throat decreases,and the proportion of oil-bearing pores decreases.With the increase of pore-throat ratio,the amount of all kinds of remaining oil increases,among which the most influential ones are columnar,blind-ended and cluster-shaped remaining oil.The smaller the pore-throat ratio is,the less likely columnar,blind-ended and cluster-shaped remaining oil is to exist in pore-throat.The larger the coordination number is,the less likely the membrane and cluster oil are to exist in the pore throat.The change of shape factor has a great influence on the membrane and cluster remaining oil.The larger the shape factor is,the less the membrane and cluster oil are likely to exist in the pore-throat.