雁翎油田注氮气增产机理的实验评价

为评价雁翎油田注氮气提高采收率的各种机理,进行了包括细长管模型实验、原油-氮气混合物的膨胀特性测量、注氮气驱油的物理模拟实验、地层原油-氮气间界面张力和岩石润湿性测定等室内实验和理论分析工作。结果表明雁翎油田注氮气只能是非混相驱油过程;在油、氮气间密度差及其较低界面张力作用下,氮气会比水更容易进入较小的含油裂缝中;油、氮气重力分异可采出构造顶部注入水未能波及到的剩余油和驱动水淹区被重力(油水密度差)捕集的残余油;注氮气改变了流动方向,降低了裂缝系统中的残余油量;原油溶气的膨胀起到了降低缝洞中残余油量的作用;注氮气的效果对其注入速度是敏感的。预计雁翎油田注氮气能获得增产效果,但是,注氮后,较大的缝洞系统中留有13%以上的残余油饱和度。

LABORATORY EVALUATION OF THE MECHANISM OF THE INCREASED OIL RECOVERY WITH NITROGEN INJECTION FOR YANLING OILFIELD

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.