Case Study: TuffTRAC Tractor’s Reverse Tractoring Frees a Stuck Gun String, Offshore Norway

Force effectively applied at the stuck point allows retrieval and resumption of job for successful completion

Challenge: Free a gun string that became stuck on the first descent at a seating nipple in a highly deviated well.

Solution: Use the reverse tractoring capability of the robust TuffTRAC cased hole services tractor to effectively apply force directly at the stuck point.

Result: Successfully retrieved the stuck gun string by using the TuffTRAC tractor in reverse mode and then ran back into the well to perforate the intervals below the stuck point in the completion.

Guns stuck in seating nipple

An operator needed to perforate a 1,130-ft pay zone in a highly deviated well offshore Norway. A SafeJet gun string conveyed on the TuffTRAC cased hole services tractor was selected for multiple runs to achieve the required perforation hole size in the liner with one shot every 23 ft. Of the total planned 72 shots, 5 would be below a seating nipple.

However, on the first descent for correlating the gun string with the completion schematic, the gun string became stuck at 11,758 ft, where the seating nipple reduced the internal diameter of the well. Maximum safe pull was applied to the cable, but because the job was conducted using an offshore mast for which the load limit was 5,500 lbf, the pull was much less than the 7,720-lbf safe working load of the cable. The gun string remained stuck.

Reverse tractoring with traction control

The simple, robust TuffTRAC cased hole services tractor is the shortest tractor available in the industry and the only one with reverse tractoring and traction control capability in highly deviated wells. The TuffTRAC tractor delivers versatility at low power requirements but can achieve a maximum speed of 3,200 ft/h.

Force successfully applied at the stuck point

Reverse tractoring can be a complicated process, with the concern of running over the cable, which would make it difficult to pull the string out of the well. The network connectivity at the offshore rig enabled real-time support from a tractoring expert based at the Schlumberger Conveyance and Surface Equipment Center in Texas.

Prior to reverse tractoring, surface tension was decreased to 3,100 lbf. The TuffTRAC tractor then started moving up at a speed of 3,000 ft/h, and the slack cable was picked up by moving the cable winch in the up direction at 500 ft/h. While tractoring up, the TuffTRAC tractor exerted an upward pull of approximately 520 lbf at the stuck point.

The force applied by the TuffTRAC tractor at the stuck point was more effective than the thousands of pounds of force applied at the surface and the gun string was freed. Based on the success of freeing the gun string by using the reverse tractoring capability of the TuffTRAC tractor, the operator had the confidence to run back in the well and successfully perforate the intervals below the stuck point in the completion, completing perforation of the 1,130-ft zone as planned in multiple runs.

Download: TuffTRAC Reverse Tractoring Frees a Stuck Gun String, Offshore Norway (0.20 MB PDF)

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