Performance evaluation of oil displacing agents for primary-minor layers of the Daqing Oilfield

A series of experiments were conducted to investigate the molecular coil dimension(Dh)and molecular configuration of partially hydrolyzed polyacrylamides(HPAM),surfactant/HPAM system,and a living polymer.Compatibility between the polymer coils and the porous media was evaluated by instrumental analysis and laboratory simulation methods.Meanwhile,the performance of chemical flooding was investigated.Results indicated that the Dh decreased with an increase in water salinity and increased with an increase in polymer concentration.In aqueous solution,the polymer presented threedimensional reticular configuration and exhibited a fractal structure characterized by self-similarity.The polymer in the surfactant/HPAM system was mainly in the form of “surfactant-polymer” complex compound and the living polymer had an irregular “flaky-reticular” configuration which resulted in relatively poor compatibility between the molecular coils and the porous media.The type of oil displacing agent and its slug size influenced the incremental oil recovery.For the same oil displacing agent,a larger slug size would lead to a better chemical flooding response.Given the final recovery efficiency and economic benefits,high-concentration polymer flooding was selected as the optimimal enhanced oil recovery(EOR)technique and the incremental recovery efficiency was forecast to be 20％.