The invention relates to a method combining
coiled tubing with supercritical CO2 for jet-flow sand washing plugging removal. The method uses the supercritical CO2 as flushing fluid to carry out jet-flow sand washing plugging removal for a shaft or an oil casing. When a supercritical CO2 jet-flow is combined with the
coiled tubing to carry out supercritical CO2 jet-flow sand washing plugging removal, pressure relief is not needed in the trip process, the
coiled tubing can directly work with pressure, and the working procedure and the time are saved. The
fluid viscosity of the supercritical CO2 is low, the
surface tension of the supercritical CO2 is close to zero, and the
diffusion coefficient of the supercritical CO2 is large, so that the supercritical CO2 can easily enter into tiny pores and cracks to dissolve
polymer organic matters and other impurities, and the cleaning is more thorough. And, above all, the supercritical CO2 does not have any
pollution to a reservoir, the
viscosity of
crude oil can also be reduced after the supercritical CO2 enters into the reservoir, the permeability of the reservoir is increased, and the yield and the
recovery ratio are increased. Thus, the supercritical CO2 is especially suitable for downhole plugging removal working of
unconventional oil-gas reservoirs such as
low permeability oil-gas reservoirs, pressure-depleted oil-gas reservoirs,
coal gas reservoirs,
shale gas reservoirs, tight sandstone gas reservoirs, heavy oil reservoirs and the like.