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为了探索缝洞型碳酸盐岩油藏水驱开发后期提高采收率技术,设计并制作了满足相似性条件的二维可视化物理模型,在此基础上研究了水驱后剩余油类型、分布规律及注氮气启动剩余油规律,分析了注气速度、注气方式(恒速注气、水气交替、间歇注气和脉冲注气)和注入井别共3类因素对氮气启动剩余油效果的影响。实验结果表明:缝洞型油藏水驱后剩余油类型可分为4大类:阁楼油、未波及区域剩余油、绕流油和油膜。注入的氮气由于重力分异作用能最大限度地替换出阁楼油,大大提高最终采出程度。注入方式、注入井别和注入速度等因素对气驱效果也有明显影响。不稳定注气比常规恒流速注气驱油效果好,水气交替效果尤其显著;高注低采的驱油效果明显好于低注高采;同时,合理适中的注气速度有助于提高采收率。
In order to explore the technology of enhanced oil recovery in the late stage of waterflooding of fractured-cavity carbonate reservoirs, a two-dimensional visualized physical model satisfying the similarity conditions was designed and fabricated. On the basis of this, the types and distribution of residual oil after waterflooding Regularity and the rule of starting the remaining oil with nitrogen injection, the effects of gas injection velocity, gas injection methods (constant gas injection, alternating water and gas, intermittent gas injection and pulsed gas injection) Impact. The experimental results show that the residual oil types after fractured-cavity reservoirs are divided into four major categories: attic oil, remaining oil in unswept areas, bypass oil and oil film. Nitrogen injected due to gravity differentiation can maximize the replacement of the attic oil, greatly increasing the degree of final recovery. Injecting methods, injection wells and injection speed and other factors have a significant impact on the gas drive effect. Unstable gas injection is more effective than conventional constant-flow gas injection and oil displacement, and the alternation of water and gas is especially remarkable. The displacement effect of high injection and low extraction is obviously better than that of low injection and high production; meanwhile, reasonable and moderate gas injection speed can help to improve Oil recovery.