A 2D Visualization Study of Polymer-Alternating-Gas Flood for Heterogeneous Reservoirs

Abstract

Abstract Miscible gas flooding is an effective enhanced oil recovery method, but its sweep efficiency is low due to gravity segregation and viscous fingering. This issue is worse in reservoirs with a high-level heterogeneity. Water-alternating-gas (WAG) injection is often applied to improve sweep efficiency, but with limited success. Polymer flooding is a proven approach to improve sweep efficiency. This study aims to evaluate the performance of CO2 Polymer-Altering-Gas (CO2-PAG) floods through a series of visualized experiments conducted at the lab scale. Simulations were employed to optimize the injection schedule of CO2-PAG. The experiments included continuous gas (CG), WAG, and PAG injection in 2D heterogeneous sand-packs. To visualize and understand the performance of CO2-PAG, a 2D view cell was used, and a layered heterogeneous sand-pack was constructed. During water flooding, the layer with higher permeability was highly swept and the layer with lower permeability was minimally swept. In PAG flooding, the polymer solution selectively swept the lower portion of the higher permeability layer, while the solvent predominantly swept the upper portion of the higher permeability layer. A small portion of the solvent also entered the upper part of the low permeability region. PAG flooding exhibited a higher swept area (than CG and WAG), leading to increased incremental oil recovery. However, gravity segregation remained a challenge, leaving a significant portion of the lower permeability layer upswept. The simulation results show that the injection schedule with more 5 PAG cycles had the highest incremental oil recovery. The introduction of tapering slug sizes did not significantly impact the performance of PAG. These findings provide valuable insights into optimizing the PAG process for enhanced oil recovery.