Impacts of CO2 injection speed on two-phase flow and physical parameters in porous sandstone

Abstract We conducted a comprehensive experimental study on the effect of the CO2 injection rate (flow rate: represented by the macroscopic capillary number, Nc) on CO2 saturation ( S C O 2 ) and the CO2 distribution in porous, brine-saturated Berea sandstone. We measured two independent geophysical parameters, P-wave velocity (Vp) and electrical resistivity (ρ*), to monitor the two-phase flow. Vp showed clear dependency on S C O 2 in the transition zone between the capillary limit (CL) and the viscous limit (VL), but not near the CL. The V p − S C O 2 relationship showed that the characteristic size of connected CO2 volumes decreased with increasing Nc, whereas resistivity increased continuously with increasing S C O 2 . Therefore, resistivity is sensitive to S C O 2 under flow conditions between the CL and VL. The ρ*– S C O 2 relationship showed that CO2 penetration increased with increasing Nc. These results indicate that we can use Vp and ρ* to monitor CO2 flow in pore spaces because the injected CO2 forms pathways and replaces brine under a wide range of Nc values.