EXPERIMENTAL INVESTIGATION OF SIMULTANEOUS WATER AND CO2 (SWACO2) INJECTION FOR OIL RECOVERY IN IMMISCIBLE AND NEAR-MISCIBLE CONDITIONS: A COMPARATIVE STUDY

A simultaneous water and CO2 injection to a dead crude oil has been performed on sandstone cores to evaluate oil recovery under secondary immiscible, secondary near-miscible, tertiary immiscible, and tertiary near-miscible injection modes. It is demonstrated that secondary SWACO(2) injection as well as tertiary flood is an effective method for oil/residual oil recovery from oil-saturated/water flooded porous media. In near-miscible condition, oil recovery is higher than in immiscible condition because there is another active pore-scale production mechanism in near-miscible injection besides volumetric displacement mechanism. In secondary near-miscible SWACO(2) injection, the ultimate oil recovery increases by increasing SWAG ratio from 0.2 to 0.4 but due to some limits, e. g., topological effects, prohibiting contact of injected gas with residual oil in pores, altering SWAG ratio from 0.4 to 0.6 showed no essential effect on ultimate oil recovery. Secondary SWACO(2) injection can recover higher fraction of oil than tertiary SWACO(2) injection. This higher oil recovery results from the oil being more accessible by injected gas due to less water-shielding effects. The results of this work can be helpful to better recognition and selection of gas-based oil recovery methods to be implemented in depleted reservoirs.