减氧空气重力稳定驱驱替机理及与采收率的关系

Experimental investigation on stable displacement mechanism and oil recovery enhancement of oxygen-reduced air assisted gravity drainage

采用二维可视化模型开展减氧空气重力驱(OAGD)实验,分析重力、毛细管力与黏滞力对油气界面运移特征的影响;开展了长岩心驱替实验,研究邦德数、毛细管数、低温氧化反应对OAGD采收率的影响,在此基础上引入低温氧化数并建立了其与采收率的关系。研究表明,油气前缘形态与变化规律主要受重力、毛细管力与黏滞力的综合影响,邦德数一定(4.52×10^−4)时,油气前缘形态受毛细管数大小控制:毛细管数小于1.68×10^−3时,油气前缘稳定;毛细管数大于2.69×10^−2时,油气前缘呈黏性指进;毛细管数为1.68×10^−3~2.69×10^−2时,油气前缘呈毛细管指进。OAGD稳定驱气体突破前,重力数越高、毛细管数越低,采收率越高,采收率主要受重力影响,可通过降低注气速度提高采收率;气体突破后,重力数越低、毛细管数越高,采收率越高,采收率主要受黏滞力影响,可通过提高注气速度提高采收率。低温氧化数与采收率具有良好的相关性,可用于预测OAGD采收率。

The effects of gravity,capillary force and viscous force on the migration characteristics of oil and gas interface in oxygen-reduced air assisted gravity drainage(OAGD)were studied through a two-dimensional visualization model.The effects of bond number,capillary number and low temperature oxidation on OAGD recovery were studied by long core displacement experiments.On this basis,the low temperature oxidation number was introduced and its relationship with the OAGD recovery was established.The results show that the shape and changing law of oil and gas front are mainly influenced by gravity,capillary force and viscous force.When the bond number is constant(4.52×10^-4),the shape of oil-gas front is controlled by capillary number.When the capillary number is less than 1.68×10^-3,the oil and gas interface is stable.When the capillary number is greater than 2.69×10^-2,the oil and gas interface shows viscous fingering.When the capillary number is between 1.68×10^-3 and 2.69×10^-2,the oil and gas interface becomes capillary fingering.The core flooding experiments results show that for OAGD stable flooding,before gas breakthrough,higher recovery is obtained in higher gravity number and lower capillary number.In this stage,gravity is predominant in controlling OAGD recovery and the oil recovery could be improved by reducing injection velocity.After gas breakthrough,higher recovery was obtained in lower gravity number and higher capillary number,which means that the viscous force had significant influence on the recovery.Increasing gas injection velocity in this stage is an effective measure to improve oil recovery.The low temperature oxidation number has a good correlation with the recovery and can be used to predict the OAGD recovery.