关键词: 雁翎油田, 裂缝性油藏, 注氮气, 增产机理, 实验室评价

Abstract: In this paper, laboratory experiments, including slim-tube tests, swelling measurement of oil-nitrogen mixture, physical modelling of oil displace ment by nitrogen injection, reservoir oil-nitrogen interfacial tension measure ment and wettability determination, as well as a theoretical analysis based on the above results were carried out to evaluate the possible mechanisms of enhanced oil recovery by nitrogen injection for Yanling Oilfield.The results show that oil displacement with nitrogen injection in Yanling Oilfield will certainly be an immiscible process.A result of higher density difference and lower interfacial tension between oil and nitrogen compared to the oil-water system will result in a nitrogen penetration into smaller oil-bearing fissures.Under gravity segregation, some of the top-oil which can't be swept by water injection will be produced and the residual oil tapped by gravity(water oil density difference)in watered-out area will be displaced.Gravity segregation in top-nitrogen injection will decrease residual oil saturation trapped in fractures after water flooding.Swelling of the nitrogen-dissolved in oil will reduce residual oil in fractures and vugs.The effect of top-nitrogen injection is sensitive to injecting rate.Finally, it is expected that nitrogen injection in Yanling Field will have an effect of increasing oil recovery, but the residual oil will still be more than 13% in larger fracture-vug system after nitrogen injection.