Study on Enhanced Oil Recovery Mechanism of CO2 Miscible Flooding in Heterogeneous Reservoirs under Different Injection Methods

The mechanism by which oil recovery can be enhanced bydifferentinjection methods of CO2 miscible flooding to alleviatethe influence of heterogeneous reservoirs was studied to optimizethe injection methods, further improving oil recovery. According tothe reservoir heterogeneity characteristics of the TI oil formationgroup in Lunnan Oilfield, a 1 m double-layer long core was designedand prepared for four CO2 miscible displacement experimentswith different injection methods. By analyzing the variation in theinjection-production parameters, the displacement effects of differentinjection methods were compared, and the mechanism of enhanced oilrecovery (EOR) was summarized. The results indicate the following.① The displacement efficiency of the different injection methodslies in the following order. Alternate CO2-waterinjection, continuous CO2 flooding, cyclic CO2 flooding, and alternate CO2-hydrocarbon gas injection.② The recovery of crude oil via CO2 miscible floodingin heterogeneous reservoirs relies on both convective diffusion andmiscible mass transfer. Convective diffusion depends mainly on controlof the displacement pressure differential and the plugging of preferentialseepage channels in high-permeability areas, while miscible mass transferdepends mainly on the swept range of the convective diffusion andthe degree of miscibility between CO2 and crude oil. ③To improve the recovery efficiency of CO2 miscible floodingin heterogeneous reservoirs, it is necessary to choose an injectionmethod that optimizes these two aspects.

Automated summary

This study investigates the mechanism by which oil recovery can be enhanced through different CO2 injection methods in miscible flooding to mitigate the influence of heterogeneous reservoirs. A double-layer long core was designed and prepared for four CO2 displacement experiments with different injection methods. By analyzing the injection-production parameters, the displacement effects of different injection methods were compared, and the mechanism of enhanced oil recovery (EOR) was summarized. The results indicate that the displacement efficiency of the different injection methods follows the order of alternate CO2-water injection, continuous CO2 flooding, cyclic CO2 flooding, and alternate CO2-hydrocarbon gas injection. The recovery of crude oil via CO2 miscible flooding in heterogeneous reservoirs relies on convective diffusion and miscible mass transfer, and it is necessary to choose an injection method that optimizes both aspects to improve the recovery efficiency.