Flow from gas wells is often hindered due to water loading problems as fields mature, which often require remedial completions for maintenance of well flow. Velocity and insert string completions, using coiled tubing, jointed tubular and continuous foam injection via micro strings are techniques used to prolong production from these depleted gas wells.

A wide variety of velocity and insert string operations have been performed. To date the authors' in-house experience includes a total of 32 insert/velocity strings deployments in wells offshore in the UK, and 40 in the Netherlands and the rest of Continental Europe, both offshore and on land. Nearly 20 micro strings (0.25″) have been deployed in Continental Europe during the last 3 years. The sizes of the deployed coiled tubing velocity strings range from 1.5″ OD to 3.5″ OD, and 13Cr ‘Flush Joint Liner' strings for gas wells with high CO2 content, range from 2.875″ to 3.5″.

In this paper the aforementioned technologies are summarized, based on an extensive list of case histories of jobs performed in the North Sea and Continental Europe. It describes the equipment, engineering and technologies used for installation of these strings by hanging off either below the SSSV or at surface, as well as the offshore operational challenges experienced, due to small footprint installations, the installations being NUI's (Normally Unattended Installations) and low crane lifting capacities.

The number of engineered and deployed insert/velocity strings represent a vast array of lessons learned, optimizations, and successful operations. The comparison between the different techniques offers a base for preparation and optimization of liquid unloading techniques. A decision tree has been prepared to assist in choosing the suitable installation type.

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