Effects of reservoir heterogeneity on oil displacement efficiency and spatial utilization during coordinated construction of oil reservoir-based underground gas storage

Based on the geological characteristics of the JD reservoir-based underground gas storage (UGS) facility, two-dimensional visual plate physical models representing vertical and areal heterogeneity were constructed. UGS operation was experimentally simulated under two injection-production schemes. An experimental-scale compositional reservoir model was also developed to characterize the spatial sweep patterns under different heterogeneity configurations and injection-production modes. The results show that the vertically heterogeneous model generally achieves higher oil displacement efficiency than the areally heterogeneous model. The relative sweep efficiencies of the two models depend on the injection-production scheme. Their difference is small after a single depressurization cycle, whereas the vertically heterogeneous model exhibits higher sweep efficiency after repeated depressurization cycles. Compared with a single cycle, repeated depressurization cycles increase the injection-production pressure difference and intensify cyclic flow perturbations. These effects weaken the persistent dominance of preferential flow pathways on injection-production process, promote fluid mobilization in medium- and low-permeability zones, and markedly improve sweep efficiency during UGS operation. Given vertical heterogeneity, increasing heterogeneity intensifies gravity segregation and interlayer channeling, suppresses the sweep into low-permeability zones, and reduces sweep efficiency. Given areal heterogeneity, by contrast, increasing heterogeneity enhances the flow conductivity of high-permeability zones and improves displacement effectiveness within the swept areas, thereby increasing the overall sweep efficiency. Accordingly, stratified injection-production combined with graded pressure drawdown is recommended for vertically heterogeneous reservoirs to suppress channeling through high-permeability zones and improve the utilization of low-permeability zones. For areally heterogeneous reservoirs, optimized well placement and zonal injection-production should be combined with multistage depressurization cycles to improve storage-capacity utilization efficiency and operational stability.