Development And Evaluation Of CO₂ Foam System In Low Permeability Reservoir Of Block X

In recent years,carbon dioxide flooding has been gradually applied in low permeability reservoirs.Low permeability reservoirs have strong heterogeneity and large carbon dioxide mobility.These factors greatly affect the oil displacement effect of carbon dioxide flooding.Carbon dioxide foam system has good flow control ability.Carbon dioxide foam flooding has become a common method to improve oil recovery in oil fields,and has achieved good results.In this paper,taking the low permeability reservoir in X block of oilfield as an example,aiming at the characteristics of low permeability,strong heterogeneity,high formation temperature and high salinity of formation water,there is viscous fingering phenomenon during gas injection development.Based on this,a CO₂ foam system suitable for the formation conditions is developed.A series of common foaming agents were screened by airflow dynamic foam analysis method with foaming volume,half-life and foam comprehensive index as indexes to measure foam performance.The formula of ternary composite foam system was developed:0.5%CQS-1/LH-1（4:6）+0.15%DQL+0.15%NS-2.Based on the developed ternary composite foam system formula,the performance evaluation and microstructure analysis of oil resistance,salt resistance,acid resistance and adsorption resistance of the foam system were carried out.The physical simulation experiments of continuous CO₂ flooding and CO₂-foam alternating flooding parallel cores were carried out by using low permeability cores.The performance evaluation results of the foam system show that the selected foam system has good temperature resistance and high foam comprehensive index.As the oil saturation increases,the foaming ability gradually decreases,and the foam half-life first decreases and then increases.The foam system has good oil resistance.In the range of salinity investigated,the foaming volume is basically not affected by salinity,and the half-life decreases slightly and then increases,with excellent salt resistance.Two kinds of adsorption sand were used for anti-adsorption experiments.The addition of foam stabilizer DQL and NS-2 had a certain inhibitory effect on the adsorption of foaming agent in sandstone.The optimized foam system has the best foam performance at a gas-liquid ratio of 1:1,and maintains the ability to stabilize the foam and reduce the oil-water interfacial tension and good acid resistance.By observing the microstructure of the foam system,a dense dendritic space network structure was formed after adding the foam stabilizer,which made the intermolecular interaction more compact and played a better foam stabilizing role.The results of oil displacement experiments show that the total recovery rate of CO₂ and foam alternate flooding core flooding is 52.05%,and the oil displacement effect is better than that of CO₂flooding,and the total recovery rate is increased by 17.53%.The recovery rate of CO₂ and foam alternate flooding low permeability core is 29%higher than that of CO₂ flooding alone,and the foam system has good profile control effect.Based on the evaluation of the developed foam system,it is clear that the foam system improves the development effect of carbon dioxide flooding,effectively expands the swept volume of CO₂ flooding in low permeability reservoirs,and has important guiding significance for the development of CO₂ flooding and CO₂ foam flooding in similar reservoirs.