延长油田特低渗透浅层油藏注CO_2提高采收率技术研究

Enhanced oil recovery of shallow extra-low permeability reservoir in Yanchang Oilfield by CO_2 injection

针对延长油田特低渗透浅层油藏储层物性差、破裂压力低、注水开发效果差等开发难点,为探讨注二氧化碳提高采收率的可行性,利用复配原油通过室内实验研究了地层条件下溶解不同含量CO2对原油高压物性的影响,并通过数值模拟技术对注气量、注入速度、注入方式、段塞大小及气液比等注气参数进行了优化.结果表明:CO2能很好地改善原油性质,CO2溶解能力强,能有效增加地层弹性能量,降低原油黏度;但是注气参数对最终采收率影响较大,气水交替注入方式优于连续注气开发,最优注气量为0.3PV,最佳注气速度为8×103m3/d.采用变气液比的方式开采,可以缩短投资回收期.该研究结果对延长油田特低渗油藏及类似油田的注气高效开发具有一定的指导作用.

The shallow extra-low permeability reservoir in Yanchang Oilfield is characterized as poor physical property and low formation fracture pressure,so it is of poor water flooding result.In order to study the feasibility of carbon dioxide injection in this area,the effects of the carbon dioxide injection of different amount on the physical properties of the crude oil under reservoir conditions are studied by the laboratory experiments of compounded oil.The injection parameters,including gas injection volume,gas injection rate,gas injection pattern,slug size and gas-to-liquid ratio,are optimized by numerical simulation method.The results show that,carbon dioxide can improve the physical properties of the crude oil:It has good dissolving ability,increase the elastic energy of formation and decrease the viscosity of the crude oil.But the operating parameters have great influence on ultimate recovery factor.The alternative injection of carbon dioxide and water is better than continuous carbon dioxide injection; the optimal gas injection volume is 0.3 PV; the optimal gas injection rate is 8×103 m3/d and investment payback period can be shortened by using variable gas-to-liquid ratio.The results in the study can provide the guidance to the effective development of the shallow extra-low permeability reservoire.