Numerical Simulation Research Of Carbon Dioxide And Nitrogen Gas Flooding In Low Permeability Reservoirs

In this paper,PVTI is used to determine the phase characteristics of the fluid in Eclipse software and the basic parameters such as saturation pressure,single flash steam oil ratio,formation crude oil density and ground degassing oil density are fitted,The minimum miscibility of carbon dioxide and nitrogen is predicted by a variety of empirical formulasThe homogeneous model 1,2,3 and heterogeneous model 4 are established by using the component model GEM in CMG,the effects of carbon dioxide and nitrogen composite flooding slugs,alternating proportions and subsequent water flooding on oil recovery are analyzed by using the homogeneous model 1 with a length of 1.2m.Specific results are obtained as follows,The recovery ratio of carbon dioxide and nitrogen compound flooding is simulated under different ratios,when the ratio of CO₂:N₂=4:1 and 2:1,1:1,1:2,1:4,CO₂ and N₂ have a great influence on oil recovery in the process of CO₂ flooding by adding the N₂ alternative flooding in the determination of the alternating slug and the recovery ratio of CO₂ and N₂ decreases gradually.Considering the saving of CO₂,it is suggested that the ratio of CO₂ to N₂ is 1:1.The carbon dioxide and nitrogen mixed flooding is simulated under different mixing ratios,with the mixture ratio of CO₂ and N₂,the displacement efficiency decrease when the proportion of CO₂: N₂=,4:1,2:l,1:1,1:2,1:4,0,the final displacement efficiency are: 75.55%,70.49%,66.82%,59.48%,56.51%,49.99%,it can be seen that a small amount of CO₂ in N₂ has a great influence on the displacement efficiency,When adding to a certain proportion?1:2?,the effect of increasing N₂ on the displacement efficiency is reduced.Carbon dioxide and water alternating flooding and nitrogen recovery efficiency are simulated under different mixing ratios,?1?With the decrease of nitrogen dioxide and nitrogen injection slug,the increase of nitrogen injection slug increases,and the final recovery is gradually reduced,which indicates that the injection of nitrogen has a certain influence on the recovery.?2?The intercritical injection of intercritical water and the effect of alternating injection of carbon dioxide and nitrogen did not change much.The recovery rate of subsequent water flooding is simulated after carbon dioxide and nitrogen gas flooding,the subsequent recovery of water injection can be increased by 2% after the combined flooding of carbon dioxide and nitrogen,therefore,the use of subsequent water drive after the composite drive.The above study are validated by using a 1.2m homogeneous model 2 to determine the accuracy of the results.In order to understand the effect of formation heterogeneity on the recovery of carbon dioxide and nitrogen complex,Carbon dioxide and nitrogen compound flooding are studied by using 9m homogeneous model 3 and 9m heterogeneous model 4,the basic alternating slug is 0.05 PV,the alternating ratio is CO₂: N₂ =,4: 1,2: l,1: 1,1: 2,1: 4,0.Through the study of these numerical simulations,the effect of nitrogen injection on carbon dioxide flooding is determined,the optimal ratio of carbon dioxide and nitrogen is optimized,the influence of formation heterogeneity on gas flooding to enhance oil recovery is analyzed,which provides the basic parameters for the physical model of gas flooding.