Construction Of Spontaneous Emulsifying Flooding System For Low Permeability Reservoirs And Study Of Its Oil Displacement Properties

China’s low-permeability reservoirs are rich in resource reserves,but they have poor rock properties,strong inhomogeneity and small pore throats,resulting in low replacement efficiency in low-permeability reservoirs.spontaneous emulsifying flooding is to form stable fine emulsions under the natural shearing action of the formation,which has high oil-water interfacial activity and strong emulsification effect,and shows great potential for application in low permeability reservoirs to improve recovery.In this paper,four fatty amine ethoxylate sulfonates with different structures of anionic and nonionic surfactants were prepared.Four fatty amine ethoxylate sulfonates were synthesized based on the best reaction conditions by optimizing the reaction conditions with tetradecylamine ethoxylate（5）as the raw material,among which tetradecylamine ethoxylate（5）sulfonate（H1405）showed the best temperature and salt resistance and emulsification performance.The H1405 was compounded with various types of surfactants selected,and the formulation of the spontaneous emulsifying flooding system was optimised by adjusting the compounding ratio and concentration,using interfacial tension and spontaneous emulsification experiments as evaluation indicators,with the objective of improving the recovery rate of a reservoir in a block in Changqing.The wetting performance,emulsion particle size distribution,anti-adsorption performance and oil washing performance of the spontaneous emulsified flooding system were evaluated,and finally the ability of the spontaneous emulsified flooding system to improve recovery was evaluated by core replacement experiments.The results show that the system has the best interfacial activity and self-emulsification performance when the mass ratio of H1405:OAB is 4:6,and can quickly spontaneous emulsify crude oil to form emulsion droplets with an average diameter of 0.36μm,which can smoothly pass the pore throat diameter of low-permeability reservoirs and maintain good stability after 2h.The formulation can make the oil recoverable by using a concentration of 3000 mg/L.Compared with a single system,the interfacial tension of the H1405/OAB spontaneous emulsifying flooding system is as low as 3.06×10^-3 m N/m,with a stronger wetting and reversal ability and 60%oil washing efficiency;the H1405/OAB spontaneous emulsifying flooding system maintains a low interfacial tension after 48 hours of sand adsorption.The H1405/OAB spontaneous emulsifying flooding system still maintains low interfacial tension after 48 h and has excellent anti-adsorption performance.The results show that the H1405/OAB spontaneous emulsifying flooding system in the low permeability cores can increase the recovery of crude oil by more than 30%on the basis of water drive,and the increase in recovery is as high as29.50%at 0.6 PV of segment plug drive,which has excellent recovery improvement ability.