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

Abstract

The mechanism by which oil recovery can be enhanced by different injection methods of CO 2 miscible flooding to alleviate the influence of heterogeneous reservoirs was studied to optimize the injection methods, further improving oil recovery. According to the reservoir heterogeneity characteristics of the TI oil formation group in Lunnan Oilfield, a 1 m double-layer long core was designed and prepared for four CO 2 miscible displacement experiments with different injection methods. By analyzing the variation in 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 the following. ① The displacement efficiency of the different injection methods lies in the following order. Alternate CO 2 −water injection, continuous CO 2 flooding, cyclic CO 2 flooding, and alternate CO 2 −hydrocarbon gas injection. ② The recovery of crude oil via CO 2 miscible flooding in heterogeneous reservoirs relies on both convective diffusion and miscible mass transfer. Convective diffusion depends mainly on control of the displacement pressure differential and the plugging of preferential seepage channels in high-permeability areas, while miscible mass transfer depends mainly on the swept range of the convective diffusion and the degree of miscibility between CO 2 and crude oil. ③ To improve the recovery efficiency of CO 2 miscible flooding in heterogeneous reservoirs, it is necessary to choose an injection method that optimizes these two aspects.

Optimizing Oil Recovery: A Comprehensive Review of Foam Applications in Enhanced Oil Recovery.

“…Gases utilized in gas-flooding operations, including CO2, hydrocarbons, air, and N2, typically exhibit significantly lower viscosity and density than water and crude oil. This characteristic leads to gas preferentially channeling through high-permeability zones and experiencing gravity override [20,21,22,23]. Consequently, gas flooding tends to have suboptimal volumetric sweep efficiency, especially in cases of immiscible displacement where the displacing phase has lower viscosity.…”

Numerical Simulation of Water Alternating Gas Injections (WAG) into Hydrocarbon Reservoirs:Factors Influencing Oil Recovery

“…The ratio of the water slug to the gas slug, as one of the injection parameters, strongly affects the displacement mechanism throughout the entire process. A comparison of WAG injection results with different slug sizes shows that short gas and water slugs perform better than large cycle injections in terms of efficiency and recovery performance [44][45][46][47].…”

Carbon Dioxide (CO2) Microbubble Suspension and Stabilization for Advancing Tertiary Oil Recovery

“…Despite the potential of CO 2 -based EOR, challenges such as buoyancy-driven CO 2 channeling and rapid CO 2 separation of CO 2 foam from oil limit its efficiency. , Microbubbles (MBs), with diameters ranging from 1 to 100 μm, offer a promising solution to address these limitations. While conventional CO 2 flooding can suffer from buoyancy effects causing the CO 2 to bypass oil, MBs can be strategically designed to overcome this issue.…”