Liquid CO2 for the Stimulation of Low-Permeability Reservoirs

ABSTRACT The effects of residual fluid in the stimulation of low permeability reservoirs has long been a problem. The use of conventional fracturing fluids (water or oil) in tight reservoirs, especially those considered to be dry gas sands, generally results in the loss of 50-75% of the fracturing fluid. Total recovery of the conventional fracturing fluid is usually never accomplished as the fluid becomes immobile at irreducible saturation. The use of liquid carbon dioxide (CO2) as a fracturing fluid was developed to combat the problems of fluid imbibition that are encountered with conventional fluids. The liquid CO2 fracturing system is essentially a non-damaging system that reverts to a gaseous state at static formation conditions. The CO2 is then returned to the surface under controlled rates as a gas. The result being a more rapid cleanup and evaluation of the well following the treatment.