Viscous and Gravity Effects at CO2 Injection

Scaling groups (1) gravity-viscosity ratio and (2) reservoir aspect number (RL) and their effects on CO2 injection under miscible and immiscible gas injection were evaluated by numerical simulations using data from performed laboratory experiments. Results of immiscible and miscible CO2 injection demonstrate transition from viscous towards gravity dominated flow. There was also observed an optimum corresponding to maximum oil recovery for different values of vertical permeability and viscosity ratios. At immiscible CO2 injection oil recovery was increasing with decreasing viscosity ratio, as a function of effective aspect number, RL,. On the contrary, as the RL increases, the total oil recovery decreases at constant viscosity ratio. It is observed that gravity effects dominate the flow behaviour above RL =5. At CO2 miscible injection two regions with a limiting curve were identified for values of RL < 3.6. For the reservoirs with RL > 3.6, three regions are suggested with two separating limiting curves. The region located between these two limiting curves is identified as the transition zone.