Design and parameter optimization of segmented suspension velocity string for drainage and gas production in offshore gas wells

To reduce the risk of liquid loading in a low-productivity offshore gas well in Panyu 30-1 field under restricted production proration, a drainage and gas production scheme using segmented suspended velocity-string in the borehole was proposed considering the constraints of downhole safety valve and platform lifting capacity. A critical liquid-carrying model for directional gas wells was adopted, combining with the original production string structure, downhole safety-valve position, wellhead pressure, water-gas ratio, and platform lifting capacity, the effects of velocity-string setting depth, tubing size, connection mode, flow capacity, erosion risk, and running/pulling loads on scheme applicability were analyzed, and the key process parameters were determined. The calculation results show that the velocity string improves liquid carrying mainly within the covered well section, indicating an obvious interval-dependent effect. The inner diameter of the velocity string is the key factor affecting the critical liquid-carrying flow rate, erosion risk, and flow capacity. As the inner diameter increases, both the critical liquid-carrying flow rate and maximum gas flow capacity increase, whereas the erosion rate ratio decreases. The evaluation results indicate that the velocity string with an outer diameter of 60.325 mm reduces the critical liquid-carrying flow rate to 5.3×10⁴ m³/d, meeting the drainage and gas production requirement of the target well under low production proration. The segmented suspended velocity string can boost the liquid-carrying capacity in key well sections while retaining the main structure of the original production string, providing a reference for drainage and gas production design in similar offshore low-rate gas wells constrained by downhole safety valves, wellbore drift diameter, and platform operation capacity.