Dimensional Analysis of CO2 Injection in Shale Oil Reservoirs

Carbon dioxide (CO2) injection effectively enhances oil recovery from shale reservoirs while potentially storing CO2. Several operational and reservoir parameters impact the oil recovery factor and CO2 storage efficiency. Rather than conducting extensive simulations through sensitivity analysis, dimensional analysis offers valuable insights into the dominant parameters affecting the incremental recovery factor (IRF) and CO2 storage efficiency (EF). Accordingly, we conduct a dimensional analysis of CO2 injection in shale reservoirs by defining the key dimensionless parameters, including Fourier number (Fo), diffusivity ratio (RD), and drawdown pressure (PD). We then use a multiphase, multicomponent transport model that accounts for molecular diffusion, Knudsen diffusion, and viscous flow to simulate a single cycle of the cyclic CO2 injection process at different operational and reservoir conditions. Using the simulation results, we investigate the scaling relations between key dimensionless parameters (Fo, RD, and PD) and IRF and EF. The results indicate that, IRF increases with Fo and reaches a plateau (maximum IRF) at an optimal Fo, like Fo = 0.006 at PD = 0.25 and 0.5. Beyond this point, the effect of diffusion on IRF becomes negligible. This suggests that the pressure gradient becomes the dominant recovery mechanism, particularly after the IRF reaches a plateau, where the effect of diffusion is minimal. In addition, RD shows a positive correlation with IRF, indicating that diffusion during the soak period has a favorable impact on oil recovery. In contrast, RD has little influence on EF. The relationship between Fo and EF is similar to that of Fo and IRF, where higher IRF values correspond to greater pore space available for CO2 storage due to increased oil production. This relationship highlights the dual benefit of enhanced oil recovery and CO2 sequestration, which can be better understood and optimized through the presented dimensional analysis.