Study On Profile Control System Optimization And Micro Displacement Mechanism Of Co₂ Foam

In China,the major injection gas of is nitrogen at present.Due to corrosion,gas shortage,poor stability and other reasons,CO₂ is less used in the foam flooding.At the same time,as a kind of greenhouse gas,CO₂ can not be discharged at will.Therefore,in this paper,the optimization of the CO₂ foam profile control system and the mechanism of microscopic displacement are studied based on the background of block 146 in the new oilfield.Block 146 in xinmu Oilfield has been developed since 1976 using waterflooding.It achieved a certain effect of increasing oil recovery after three times of well pattern adjustment,but the water cut in production wells hasn't been reduced largely.The whole block has entered a stage of high liquid,high water cut and high degree of recovery,which is urgently needed to change the development regime.According to a series of problems during the water flood development,such as high water,serious water channeling,low water flooding efficiency and so on.Using CO₂ foam flooding technology can be adapted to the local conditions,because the use of CO₂ gas produced by the Changling gas field can solve the problem of CO₂ gas source and realize the environmental protection development in Changling gas field at the same time.The mainly research results are as follows:?1?Through the comprehensive coefficient method,a suitable formula of CO₂ foam profile control system has been screened out:0.4%SDS + 0.1%OB-2 +?0.03%-0.06%?CMC.100mL of the formula fluid can make 665mL foam system,with the half produce time is 83min,and the comprehensive coefficient is 41396 min mL.The performance of the system was evaluated.The experimental results show that the system has good salt resistance,oil resistance,oil washing performance and good stability.?2?Core flood experiments show that the suitable gas-liquid ratio is 2:1,and the optimum injection course is 6 with 0.05PV foam concentrate and 0.1 PV CO₂ ever course.When the injection rate gets 1mL/min and the oil saturation is less than 15%,the system still has strong sealing ability.?3?Visualized microscopic displacement model was used for flow experiments.It can be observed that the formation mechanism of CO₂ foam flooding including liquid film hysteresis,necking separation and thin film segmentation.The mechanism of the breakup includes liquid film discharge,liquid film rupture and gas diffusion.The migration mechanism is divided into gas and liquid phases.The gas migration includes foam trapping and foam flow in the main channel,and the liquid phase migration is divided into volume water migration and liquid film water migration.?4?Visualized microscopic displacement model was used for oil displacement experiments.CO₂ foam flooding can be divided into three stages:prophase,metaphase and anaphase.The flooding mechanism is mainly two aspects,including expanding swept volume and improving cleaning efficiency.The CO₂ foam microscopic oil displacement experiment shows that gas-liquid ratio,injection rate and injection time of oil displacement have great influence on CO₂ foamflooding.