Study On The Mechanism Of Enhanced Oil Recovery By Cellulose Nanofibrils Enhanced CO₂ Foam

With the increasing emphasis on environmental pollution in recent years,more attention has been paid to advanced green materials.Cellulose nanofibrils is an environmentally friendly and renewable biological nano-material,which has the advantages of strong toughness,high aspect ratio,large specific surface area and easy modification,and shows great application potential in many fields.The latest research shows that the unique properties of cellulose nanofibrils can improve the stability of water-based foam.Based on this,this paper explores and constructs a new CO₂ foam system enhanced by cellulose nanofibrils,in order to improve the stability of CO₂ foam under reservoir conditions,improve foam sweeping ability and oil displacement efficiency,and thus obtain a green,environment-friendly and efficient method for enhancing crude oil recovery.Firstly,the stability mechanism of cellulose nanofibrils on CO₂ foam system was studied to guide the construction of high stability CO₂ foam system.On this basis,the EOR mechanism of carbon dioxide foam system enhanced by cellulose nanofibrils was deeply studied.The foaming and foam stabilization performance of CO₂ foam system enhanced by different concentrations of cellulose nanofibrils was evaluated.The higher the concentration of cellulose nanofibrils in the test range,the better the effect of stabilizing CO₂ foam.Microscopically,the micro-morphological evolution of CO₂ foam enhanced with different concentrations of cellulose nanofibrils shows that the higher the concentration of cellulose nanofibrils,the thicker the liquid film of CO₂ foam and the longer the time required for foam bursting.Through infrared spectrum analysis and interfacial tension test of the base liquid of carbon dioxide foam system enhanced by cellulose nanofibrils,the synergistic foam stabilization mechanism of cellulose nanofibrils and surfactant was explored.The hydrogen bond formed between cellulose nanofibrils molecules and surfactant molecules is beneficial to increase the stability of CO₂ foam.The rheological test results show that the base liquid of carbon dioxide foam system enhanced by cellulose nanofibrils and the foam produced by it have shear dilution phenomenon.Two-dimensional microscopic visualization model was used to observe the flow behavior and oil displacement law of carbon dioxide foam enhanced by cellulose nanofibrils at pore scale.The experimental results show that CO₂ foam added with cellulose nanofibrils can control the mobility of CO₂ in the formation,which is beneficial to CO₂ sequestration in the formation.Core displacement experiment shows that the carbon dioxide foam system enhanced by cellulose nanofibrils has strong plugging and profile control effects,which can expand swept volume,improve oil washing efficiency and enhance oil recovery.