Coiled tubing of drainage gas recovery technology used in shale-gas downdip horizontal wells

The horizontal section of shale gas well is completed using Ø139.7 mm casing, and due to stratigraphical and structural conditions, target A and B in some wells are more different in vertical depth, which leads to the emergence of downdip characteristics. The liquid carrying capacity in the horizontal section is poor, and with the depletion of formation energy, the liquid loading tends to accumulate in the horizontal section below the tubing shoe. As a result, gas wells are watered out and their production can be hardly restored by using gas lift, plunger and foam drainage technologies. To solve this problem, this paper selected a smaller coiled tubing and ran it into the horizontal section through the original production string to increase gas flowing velocity and improve the liquid carrying capacity in the well while applying the composite drainage gas recovery of small diameter tubing & gas lift & foam drainage to drain the liquid loading out of the horizontal section. It is indicated that Ø50.8 mm coiled tubing is suitable for the gas wells with water/gas ratio less than 1.5 m³/10⁴ m³ and Ø38.1 mm coiled tubing is suitable for the gas wells with water/gas ratio less than 1 m³/10⁴ m³. Field application shows that after the coiled tubing is ran into the middle part of horizontal section in the downdip gas well with liquid loading in the horizontal section, the change of tubing and casing pressure is stable, its gas rate for continuous liquid carrying is decreased, gas and liquid is distributed uniformly in the well, and slippage loss is reduced. In conclusion, the coiled tubing based drainage gas recovery technology can effectively solve the problem of liquid loading in the downdip horizontal section of shale gas well and ensure the continuous stable production of shale gas wells in the low-yield stage.