In the Ba-21 Block of Xinjiang oilfield，residual oil is predominantly concentrated in low-permeability zones，making CO₂ flooding a promising enhanced oil recovery（EOR）technique. However，significant reservoir heterogeneity，combined with the mobility contrast between CO₂ and crude oil，increases the risk of gas channeling. Water-alternating-gas（WAG）injection，a widely used method to mitigate gas channeling，requires further evaluation to determine its effectiveness in this setting. This study investigated the influence of WAG injection on the performance and oil recovery of CO₂ flooding under heterogeneous conditions， using natural conglomerate cores with varying permeabilities representative of Ba-21 Block. The results showed that CO₂ readily interacted with Ba-21 crude oil，enabling efficient displacement. However，elevated injection rates and permeability levels accelerated oil production while intensifying CO₂ channeling，leading to rapid declines in oil output. For the main reservoir intervals （liquid permeability ranging from 3.1 × 10-3 μm2 to 25.5 × 10-3 μm2），WAG injection with a 1∶1 slug volume ratio effectively suppressed intra-layer channeling，enhancing oil recovery by 34.1 percentage points—50.6 percentage points compared to continuous CO₂ flooding. However，as permeability increased，the flow resistance established by WAG weakened，and the presence of water reduced the extraction efficiency of CO₂ . As a result，C7—C14 alkane content in produced oil decreased. When both interlayer and intralayer heterogeneities were present，the effectiveness of WAG in controlling gas channeling was further compromised. In conglomerate cores with a gas permeability contrast of 4.1，WAG improved recovery by less than 7 percentage points. In contrast，foam flooding，offering superior mobility control，significantly enhanced following WAG injection，increasing oil recovery by 26.8 percentage points and 12.2 percentage points in high- and low-permeability cores，respectively. These findings provided theoretical and technical support for assessing WAG feasibility in Ba-21 Block and offered valuable guidance for optimizing gas channeling control strategies in similarly heterogeneous reservoirs during CO₂ flooding.