低渗透油藏CO_2、水交替驱提高采收率及其影响因素分析

Analysis on Factors of Enhancing Oil Recovery by CO_2 and Water Alternating Flooding in Low Permeability Reservoirs

低渗透油藏储层致密,水驱后期,含水率逐渐增高,驱替效率也随之降低,剩余油潜力依然较大。应用CO_2驱油技术,一方面可以较大幅度的提高采收率,同时也可将一部分的CO_2封存在地下。通过室内CO_2、水交替驱油实验以及实际生产,分析了采收率提高情况以及影响采收率提高的因素。结果表明:气水交替驱最终驱油效率51.2%~62.7%,平均58.7%,比水驱油平均高10.1%;尤其以渗透率大于1.0×10^(-3)μm^2的样品采收率提高比较显著;气水交替驱,不同渗透率岩样在注入0.5 PV的气体或者水时躯替效率提高最大;驱替压差与渗透率呈反比关系,随着驱替压差的减小驱油效率增大;低渗透油藏在实际注气生产过程中,应综合考量各类因素的影响,制定合理的注采方案。

The low permeability reservoir is tight. After water flooding,water content increases gradually and the water-oil displacement efficiency comes down while the potential of residual oil is still huge. CO_2 oil displacement technique can not only enhance oil recovery greatly,but also store partial CO_2 in the underground. In this article,the efficiency and related factors of CO_2-water alternating EOR were analyzed by laboratory experiments and practical production. The results indicate that the final efficiency of CO_2 water alternating displacement is in the range of 51.2%~ 62.7%,with an average of 58.7%,which is 10.1% higher than that of water displacement. In particular,the recovery rate of samples with permeability greater than 1.0×10^（-3）μm^2 increases significantly. The displacement efficiency of different samples with various permeability increases mostly when they are injected 0.5 PV gas or water in CO_2 water alternating displacement. In addition,the displacement differential pressure is inversely proportional to the permeability,and the oil displacement efficiency increases with the decrease of the displacement differential pressure. Above all,we should consider the impact of various factors in practical gas injection and production process of low permeability reservoirs.