Carbonated Water Imbibition Flooding: An Enhanced Oil Recovery Process for Fractured Reservoirs

Abstract

ABSTRACT Water imbibition studies were conducted on core plugs at confining pressures of 2,000 psi. Water was enriched with CO2 at different carbonation pressures, ranging from 50 to 500 psi. Conventional displacement as well as Nuclear Magnetic Resonance (NMR) methods were used to study the effects of carbonated water imbibition on oil recovery rate and ultimate recovery. The major factors influencing oil recovery by carbonated water imbibition displacement appear to be: An increase in oil mobility. An increase in core permeability in carbonate cores A reduction in the operating pressure below the bubble point pressure after the core had been allowed to imbibe the carbonated water induced a solution gas drive effect which substantially increased recovery. Carbon dioxide dissolved into the water being imbibed by the rock was found to accelerate oil recovery rates and increase ultimate oil recovery when compared to unadulterated water imbibition. Recovery rate and ultimate recovery increased as a function of the amount of CO2 dissolved into the imbibed water. Recovery time was reduced to one third when the gas liberation process was applied cyclically. This new method holds promise to increase oil production rates and oil reserves from fractured, low matrix permeability, low gas-oil ratio, oil reservoirs.