低渗透油藏CO2混相驱注采耦合波及特征及气窜阶段定量划分方法

针对CO₂混相驱注采耦合波及特征认识不清,气窜阶段无法定量识别的问题,运用数值模拟方法,分析CO₂混相驱注采耦合波及特征,明确气窜程度表征指标和划分标准。结果表明:与CO₂连续气驱相比,注采耦合开发通过增压储能、放压释能过程,地下渗流场不断变化,扩大气驱波及面积,延迟气窜时间,提高油藏最终采出程度;新方法计算的气窜阶段划分结果与矿场监测数据吻合,可作为矿场气窜阶段识别的依据;储层孔隙度越大,注采耦合开发无气采油阶段变长,气窜发育阶段推迟;生产井离注气井越近,气体突破时间越早,反九点法井网、排状井网、五点法井网进入完全气窜时间分别为3 148、4 120、5 610 d。研究成果可为低渗透油藏CO₂混相驱注采耦合开发提高采收率提供理论指导。

Sweep Characteristics of CO2 Miscible Flooding with Injection-Recovery Coupling in Low Permeability Reservoirs and Quantitative Classification of Gas Channeling Stages

As the sweeping characteristics of CO₂ miscible flooding with injection-production coupling are not clearly understood and the gas channeling stage cannot be quantitatively identified, numerical simulation was applied to analyze the sweeping characteristics of CO₂ miscible flooding with injection-production coupling and determine the characterization indicators and classification standard of the gas channeling degree. The results showed that, compared with CO₂ continuous gas flooding, the development with injection-production coupling expanded the sweeping range of the gas flooding, delayed the time of gas channeling and improved the final recovery percent of the reservoir through pressurization, energy storage, pressure release and energy release; the results of gas channeling stages calculated by the new method were consistent with the field monitoring data, which can be used as the basis for the identification of the gas channeling stage in the mine; the greater the reservoir porosity, the longer the gas-free oil production stage and the later the gas channeling development stage; the closer the production well was to the gas injection well, the earlier the gas breakthrough time was, and the duration of complete gas channeling was 3 148 d, 4 120 d and 5 610 d for the inverse nine-spot pattern, row pattern and five-spot pattern, respectively. The research results can provide theoretical guidance for the enhanced oil recovery of low permeability reservoirs under development by CO₂ miscible flooding with injection-production coupling.