低渗油藏CO_2驱开发中后期研究

Study on the middle and late stages of CO_2 flooding development in low permeability reservoirs

针对低渗油藏CO_2驱中后期因油井方向性气窜,开井时率低,以及部分高产气井计量误差大等问题,通过地层油/CO_2高压物性实验、高温高压微观模型驱替实验和CO_2-原油细管等实验研究,并结合现场资料,对CO_2驱见效规律和高产气井计量方法优化进行深入研究。结果表明:CO_2与原油混相后能大幅降低乃至消除界面张力,增强混合流体的流动性,提高驱替效率;实施气水比2∶1(注气2个月,注水1个月)的水气交替,可达到保持混相与控制气窜的双重目的;通过室内实验证实,CO_2与原油过多次接触,油相体积不断膨胀,当达到混相后,油相体积系数膨胀为1.7倍;低地混压差油藏难以实现全油藏混相,即使非油藏全混相,也能有效发挥CO_2混相驱提高驱油效率的作用,凸显CO_2驱与水驱的对比优势。

Aiming at the problems of gas channeling,low open-hole rate and large measurement errors of some high-yield gas wells in the middle and later stages of CO2 flooding in low-permeability reservoirs,through the formation oil/CO2 high-pressure physical experiment and high-temperature high-pressure microscopic model displacement experiment and CO2-crude oil thin tubes.Combined with the field data,the paper studies the law of CO2 flood efficiency and the optimization of high-yield gas well measurement methods.The results show that CO2 mixing with crude oil can greatly reduce or even eliminate the interfacial tension and thus enhance the fluidity of the mixed fluid can be improved and the displacement efficiency can be improved.The dual purpose of maintaining mixed phase and controlling gas channeling can be achieved by carrying out alternating gas-water ratio of 2∶1（2-month gas,1-month water injection）.Experiments show that after repeated contact between CO2 and crude oil,the volume of oil phase expands continuously.When the mixed phase reaches the mixed phase,the volume coefficient of oil phase expands 1.7 times.It is difficult to realize all reservoir miscibility in low land mixed pressure differential reservoir,even if non oil reservoir is not mixed phase,it also can effectively play the role of CO2 mixed flooding to improve flooding efficiency,highlighting the comparative advantage with water flooding.