Possible alteration of tight limestone rocks properties and the effect of water shielding on the performance of supercritical CO₂ flooding for carbonate formation

This work presents results obtained in a laboratory study investigating the possible alteration of tight limestone cores properties such as porosity, permeability, and wettability; and the effect of water shielding on a water driven slug of super critical CO₂. Reservoir condition corefloods were conducted using actual rock cores and fluids obtained from a field in Abu Dhabi at 4000 psia and 250°F. Recovery from core floods and the permeability and porosity before and after the flood were measured to examine the effects of SC CO₂ flood on the tight composite limestone cores. Oil samples produced in the experiments were analyzed using gas chromatography (GC) to assess the mechanism of CO₂-improved oil recovery. The characteristics of relative permeability were measured prior to and after SC CO₂ flood. Changes in the relative permeability characteristic were used to evaluate the effect of SC CO₂ flood on the limestone rock wettability alteration. Oil/water interfacial tensions (IFT) measurements as function of pore volume injected were conducted to evaluate any possible changes in interfacial forces due to the SC CO₂ flooding.