特低渗油藏不同CO2注入方式微观驱油特征

为研究特低渗油藏CO2不同注入方式的微观驱油特征和孔隙动用下限,利用核磁共振技术,分析了连续CO2驱、水驱后CO2驱以及水气交替驱后岩心的微观剩余油分布。实验结果表明,水驱后CO2驱和水气交替驱均能获得较好的驱油效果,连续CO2驱能够动用更小孔隙中的原油,水驱后CO2的注入弥补了水驱难以动用微、小孔隙(孔径小于0.5μm)中原油的缺点,水气交替驱在中孔隙(0.5~5.0μm)中取得更好的驱油效果。对于不同孔隙结构的岩心,储集层微观非均质性越强,小孔隙比例越高,不同注入方式下的孔隙动用下限也越高。综合来看,水气交替驱能够在长庆油田黄3区块长8油藏取得较好的微观驱油效果。

Microscopic Characteristics of Oil Displacement With Different CO2 Injection Modes in Extra-Low Permeability Reservoirs

In order to investigate the microscopic characteristics of oil displacement and the lower limit of the pore diameter of CO₂ injection with different injection modes in extra-low permeability reservoirs, NMR technology is used to analyze the microscopic residual oil distributions in cores for different injection modes such as continuous CO₂ flooding, CO₂ flooding after waterflooding and alternative water-gas flooding. The experiment results show that relatively good oil displacement effects of CO₂ flooding after waterflooding and alternative water-gas flooding have been gained. Continuous CO₂ flooding can displace oil in smaller pores, CO₂ flooding after waterflooding can displace oil in small pores and micropores（pore size less than 0.5 μm）which can’t be recovered by water flooding, and good effects of alternative water-gas flooding can be gained in medium pores (0.5-5.0 μm). For the cores with different pore structures, the stronger the heterogeneity of the reservoir is and the more the small pores account for, the higher the lower limit of pore diameter in different injection modes will be. As a whole, good oil displacement effects can be gained by applying alternative water-gas flooding in Chang-8 reservoir of Huang-3 block in Changqing oilfield.