Impairment mechanism of thickened supercritical carbon dioxide fracturing fluid in tight sandstone gas reservoirs

Non-aqueous supercritical CO2 (scCO2) fracturing stimulation techniques have acquired much attention in the development of tight gas reservoirs recently. However, few researches have devoted to the impact of scCO2 fracturing fluid on permeability and relevant mechanisms. In this study, phase behaviors of thickener polydimethylsiloxane (PDMS) and co-solvent kerosene in scCO2 were studied. The regained permeability investigations reveal that the low filtrated volumes of scCO2 fracturing fluid have instant and major deterioration of sandstone permeability. The regained permeability ratio reaches the equilibrium with the further increase of filtrated volumes. The compositions of scCO2 fracturing fluid also have impact on the regained permeability. Another regained permeability tests demonstrate that slick-water causes more permeability damage to lower-permeable samples, while scCO2 fracturing fluid causes more permeability damage to higher-permeable samples. The relevant mechanisms are proposed. XRD in clay swelling tests detects the existence of the clay minerals in the tight sands and eliminates the potential of clay swelling effect of scCO2 fracturing fluid. Our investigations indicate the operational feasibility of scCO2 fracturing fluid in tight gas reservoirs and the addition of high content of co-solvent should be avoided as to maintain the low permeability damage to gas reservoirs.