碳酸盐岩缝洞型油藏氮气驱提高采收率的影响因素

Influencing factors on EOR nitrogen flooding in fractured-vuggy carbonate reservoir

碳酸盐岩缝洞型油藏在开发过程中地层能量衰竭明显,氮气驱可以有效地补充地层能量,并增强采出能力;但只有合适的注入速度、注入时机和注入方式等才能使氮气驱达到最好的驱替效果。利用地质构造和生产动态资料建立缝洞型油藏的二维可视化地层仿真剖面模型,在室内底水能量不足时,进行了氮气驱注入速度、注入时机和注入方式等因素对采收率的影响程度研究,结果表明,氮气驱注入速度对波及范围和气窜控制有较大的影响,过大过小都会使最终采收率偏低;氮气驱注入时机的早晚影响水驱效果,进而影响采收率,注入时机过早水驱效果差,注入时机过晚气驱效果差;连续氮气驱、氮气—水交替、氮气—活性水交替等注入方式可以将采收率从20%分别提高到47.09%,60.08%和61.45%。

Formation energy in the carbonate fractured-vuggy reservoir becomes less along with the exploitation. Nitrogen flooding can effectively complement the formation energy,and enhance the capacity of production. Only appropriate injection rate,injection timing and injection mode can achieve the best displacement effect of the nitrogen flooding. A visualized physical simulation model of the fractured-vuggy reservoir was designed based on geological structure data and dynamic production data. Influencing factors on nitrogen injection including injection rate,injection timing and injection mode were analyzed when bottom water energy is not enough in laboratory. The results show that the injection rate has great influence on sweep efficiency and gas channeling and the ultimate recovery efficiency would be low under inappropriate injection rate.Injection timing has influence on water flooding and recovery efficiency. If the opportunity of nitrogen injection is too early,water flooding effects will be poor;and if the opportunity of nitrogen injection is too late,nitrogen flooding effects will be poor. Under the condition of recovery efficiency of 20% by water drive,continuous nitrogen injection can improve the recovery efficiency to 47.09%,while alternating injection of water and nitrogen can improve the recovery efficiency to 60.08%,and alternating injection of surfactant water and nitrogen can improve the recovery efficiency to 61.45%.