边底水气藏注CO_2提高采收率技术

Enhanced Oil Recovery by CO_2 Injection into Gas Reservoir with Edge and Bottom Water

开发中后期,边底水气藏地层条件相对较为复杂,压力降低和圈闭变化引起下部地层水填补了气体的采出,在衰竭开采情况下采收率会相当低。通过向储层中注入CO_2可以控制边底水的均匀推进,解决CO_2气体埋存的同时还可以提高气藏采收率。结合2个国外气田的CO_2回注实例,重点阐述了典型储层条件下CO_2和CH_4的流体特征、超临界CO_2驱替天然气的室内实验和数值模拟研究现状。数据表明,CO_2注入井在储层下倾、采气井在上倾方向布井,羽流会沿气水界面向采气井轻微锥向流动,CH_4采气量明显提高,并可能减少由于水侵所带来的剩余气损失;向气藏中回注CO_2应尽可能早,这样有利于保持地层压力和气体流动,减小下部地层水侵入储层,延长开采时间;底水气藏最佳注入时机应该在气藏开采3年和4年后。该研究成果对高效开发边底水气藏具有一定指导作用。

In the middle and later stage of development,the gas reservoirs with edge and bottom water are facing with lower formation water invasion for the pressure drop and trap change in the relatively complex formation conditions,and the recovery efficiency is much lower in the case of depletion development.CO2 injection into the reservoirs can control uniform invasion of the edge and bottom water,and solve the geological storage of CO2 beneath,and enhance oil recovery in the meantime.Combined with 2 cases of CO2 re-injection in the foreign gas fields,the fluid characteristics of CO2 and CH4 under typical reservoir condition and the research status of laboratory experiment and numerical simulation about natural gas displacement by super-critical CO2 were discussed.The data indicate that CO2 injection wells should be placed in the downdip direction of the reservoir and gas producer should be placed in the updip of the reservoir,plume of injected CO2 may flow as cone from injection well to gas producer along gas-water interface,and CH4 gas production improves significantly and residual gas loss because of water invasion may reduce.CO2 should be injected into gas reservoir as early as possible that is beneficial to maintain reservoir pressure and gas flow,to decrease bottom formation water invasion into reservoir.Production time may be prolonged.The best injection time should be three or four years after gas production in the bottom water gas reservoir.The results have certain guiding role on developing gas reservoir with edge and bottom water more efficiently.