Design and Assessment of Channeling Control Systems for Enhanced CO₂ Storage in Fractured Reservoirs

To address the issues of suboptimal mobility control and unstable displacement fronts in traditional WAG technology for continental fractured heterogeneous reservoirs, which lead to severe gas channeling, a novel enhanced channeling control system utilizing a CO₂-responsive gel-assisted WAG was designed. The novelty of this approach lies in the integration of in situ gel plugging with a tapered WAG ratio, which synergistically enhances recovery by dynamically improving mobility control and stabilizing the displacement front. Under simulated reservoir conditions, the injectivity and plugging performance of M-Gel for grade I-III fractures were evaluated. Results demonstrate that M-Gel exhibits excellent injectivity and effectively plugs grade I-III fractures, achieving a plugging efficiency of up to nearly 80% for the most intensely fractured grade I fractures. Subsequently, for a reservoir model with grade I fracture development, an M-Gel-assisted WAG enhanced channeling control system was constructed. Orthogonal experiments were employed to optimize the water-gas ratio injection strategy and gel concentration. The study found that adopting a tapered injection mode with the water-gas ratio decreasing from 3:1 to 1:1 and an M-Gel concentration controlled at 0.5 wt % yields significant gas channeling inhibition. Under this system, gas breakthrough time is significantly delayed, interlayer utilization effectiveness is enhanced, and efficient utilization of the high-permeability layer is maintained at 78.5%. Meanwhile, the utilization degree of the low-permeability layer increases markedly from 9.6% under conventional WAG to 21.4%, representing an increase of 11.8%. The overall recovery factor reaches 60.8%. Microscopic visualization model displacement experiments suggest that using this system, the residual oil in microscopic pore throats is markedly reduced. Analysis indicates that the designed enhanced channeling control system effectively leverages the synergistic effects of gel-induced fracture plugging and multicomponent WAG-mediated flow field regulation, suppressing gas channeling caused by strong heterogeneity in fractured reservoirs and thereby further improving crude oil recovery.