Method combining coiled tubing with supercritical CO2 for jet-flow sand washing plugging removal

Abstract

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.

Description

technical field [0001] The invention relates to a method for sand flushing and plugging removal of oil wells, in particular to a coiled tubing supercritical CO 2 The invention discloses a method for removing plugging by sand washing, which belongs to the field of oil plugging removal. Background technique [0002] Sand production in oil and gas wells, residual fracturing sand, wellbore contamination and clogging have always been common concerns of operators around the world. As early as the beginning of the 20th century, people discovered this problem and have been working hard to find the best solution. . [0003] At present, both at home and abroad, water (adding some additives if necessary) is used for well flushing operations. When encountering pressure-depleted reservoirs, nitrogen foam or air foam is often used for underbalanced well flushing, which alleviates the problem to a certain extent. Production decline problems due to wellbore plugging. However, this type o...

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Problems solved by technology

However, this type of well flushing method does not fundamentally solve the problem of wellbore blockage. For example, after water enters the reservoir, it will cause great damage to water-sensitive oil and gas reservoirs. Although foam flushing can reduce the bottom hole pressure, the quality of foam It is difficult to control, and it is easy to cause bottomhole pressure fluctuations, which will cause greater damage to the reservoir; in addition, the most important type of wellbore blockage is the blockage of high molecular organic matter such as asphalt mixed with sand, clay, etc., some of which settle at the bottom of the well, and some adhere to On the well wall, the oil flow channel is seriously blocked. When this kind of blockage is removed by water jet, because of the strong viscoelasticity of asphalt and other high-molecular organic substances, it is difficult for water jet to break such substances, and it is also difficult to remove this kind of blockage. Substances are completely removed

[0004] During the long-term production of oil and gas wells, due to the high salinity of the formation water, it is easy to scale on the oil casing, and the thick scale will lead to failure of normal production

Traditional descaling includes mechanical descaling, chemical descaling, water jet descaling, etc. Traditional mechanical descaling is easy to cause damage to the oil casing, chemical descaling will also cause corrosion to the oil casing, water jet descaling Although the damage to the oil casing is small, the water jet cannot completely remove the hard scale. At the same time, it requires a high pump pressure. If the abrasive jet is used for descaling, the oil casing will be penetrated if the pressure is not well controlled.

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