A New Method For Testing The Miscibility Pressure Of CO₂ Miscible Flooding

Among the proven reserves in China,the proportion of low-permeability oil reservoirs and ultra-low permeability oil reserves are very high,accounting for more than two-thirds of the country's total reserves,and the development potential is huge.However,conventional water flooding or solvent flooding was used to develop low-permeability reservoirs.These problems have a serious impact on the improvement of oil recovery.Gas injection is an important means to improve the development of oil recovery in low permeability oil fields.Miscible flooding accounts for an absolute proportion in gas flooding extraction projects.At present,gasses commonly used in miscible flooding include hydrocarbon gas,air,N2,and CO2.Through long-term research,it has been found that the minimum miscibility pressure of crude oil injection of CO2 is smaller than other gases(hydrocarbon gas,air,N2),and CO2 is more miscible than other gases(hydrocarbon gas,air,and N2).Therefore,C02 is more suitable for Miscible flooding enhances recovery.At the same time,with the development of industry,the emission of CO2 gas increases rapidly,and the CO2 gas emission is the main cause of global warming.Note CO2 can not only increase oil recovery but also reduce CO2 emissions by reducing CO2 emissions.In view of the deficiencies of the existing test methods,this paper proposes multiphase miscibility of CO2 injected with crude oil in a multi-stage contacted heterogeneous tube,and tests the interfacial tension of multistage contact contaminating tube gas with crude oil,and determines whether or not miscibility is determined by interfacial tension.At the same time,it also demonstrated the feasibility of using this method.Based on the existing methods of testing CO2 miscible flooding MMP test,this paper summarizes the deficiencies of the existing methods and proposes a new method for testing and testing CO2 miscible flooding MMP.The main understanding and results obtained are as follows:(1)It is proposed to inject multi-stage contact CO2 with crude oil in a multi-stage contact heterogeneous tube,and measure the interfacial tension between the gas and the crude oil in the multiphase contact and use the interfacial tension to determine whether or not to use the miscible method.(2)Through the numerical simulation software,the height simulation in the multi-stage contact miscible tube,the parameters of the multi-stage contact tube are obtained,and the multi-stage contact miscible tube is designed and manufactured.The device can combine the advantages of the capillary tube method and the interfacial tension method.In the multi-stage contacting heterogeneous tube,the simulated CO2 contacted with the crude oil in the porous medium.At the same time,the interfacial tension of the mixed-phase tube gas and the crude oil can be measured.At the same time,the maximum pressure that the multi-stage contacted heterogeneous tube can withstand is 40 MPa.(3)Using the new method to test the minimum miscibility pressure of the CO2-crude oil system and comparing it with the slim tube method,the minimum miscibility pressure difference obtained is very small,which proves that the new method is feasible.At the same time,the new method has the advantages of convenient operation,low fuel consumption,short time,and easy disassembly.(4)When the pressure reaches the minimum miscibility pressure of the C02-crude oil system,the crude oil slowly disperses in the gas phase and has an irregular shape.