Tripping under pressure for coiled tubing velocity string and reuse

Drainage gas recovery technique using velocity string has become a major means for drainage gas production in Sulige Gasfield, addressing the problem of drainage gas production in gas wells with standing fluids. In line with depletion of gas well energy during development of gas fields and worsening of fluid carrying efficiency in gas well with small gas production, research has been done on the technology of tripping out under pressure of velocity string of coiled tubing, and the technical program for tripping out under pressure of velocity string was designed, and key tools were developed like in-pipe plug, puller for external slips, etc., which have addressed the core problem of block-off inside the velocity string and unfreezing by lifting. Experiment on tripping out the velocity string under pressure was successfully conducted in Sulige Gasfield; the tripped out string, after performance assessment, can meet the requirement of drainage gas recovery and can be run in hole again as production string.