Experimental investigation on plugging performance of CO_2 microbubbles in porous media

To further improve carbon dioxide enhanced oil recovery CO_2-EOR efficiency in heterogeneous reservoirs, the use of CO_2 microbubbles as a temporary blocking agent is attracting widespread interest due to their significant stability. This study aims to investigate the plugging performance of CO_2 microbubbles in both homogeneous and heterogeneous porous media through a series of sandpack experiments. First of all, CO_2 microbubble fluids were generated by stirring CO_2 gas diffused into polymer (Xanthan gum (XG)) and surfactant (Sodium dodecyl sulfate (SDS)) solution with different gas: liquid ratios. Then, CO_2 microbubbles fluids were injected into single-core and dual-core sandpack systems. The results show that the rheological behaviors of CO_2 microbubble fluids in this study were followed the Power-law model at room temperature. The apparent viscosity of CO_2 microbubble fluid increased as the gas: liquid ratio increased. CO_2 microbubbles could block pore throat due to the “Jamin effect” and increase the resistance in porous media. The blocking ability of CO_2 microbubbles reached an optimal value at the gas:liquid ratio of 20 % in the homogeneous porous media. Moreover, the selective pugging ability of CO_2 microbubbles in dual-core sandpack tests was significant. CO_2 microbubbles exhibited a good flow control profile in the high permeability region and flexibility to flow over the pore constrictions in the low permeability region, leading to an ultimate fractional flow proportion (50%:50%) in the dual-core sandpack model with a permeability differential of 1.0:2.0 darcy. The fractional flow ratio was considerable compared with a polymer injection. At the higher heterogeneity of porous media (0.5:2.0 darcy), CO_2 microbubble fluid could still establish a good swept performance. This makes CO_2 microbubble fluid injection a promising candidate for heterogeneous reservoirs where conventional CO_2 flooding processes have limited ability. This finding would be helpful in developing the utilization of CO_2 microbubbles in EOR operation by better understanding their plugging mechanism in porous media.