During the restoration process of a high temperature gas producer well, offshore Brazil, it was detected that its production tubing was stuck due to scale deposition. An attempt to pull the string using an offshore completion rig was unsuccessful. The use of alternative methods like wireline chemical cutters, string shots and thru-tubing tools with elastomer rubbers was not possible due to the high bottom hole temperature of the well (363 °F). With this scenario, the solution was to use coiled tubing in order to cut the string above the free point.
The first challenge for this coiled tubing intervention was the production tubing metallurgy, Cr-22, which has highly ductile and carbides embedded in its matrix. These properties cause the adherence of chips on the cutter blades and contribute to accelerated wear on the mechanical cutter.
The second challenge was the constraint of having to use lower torque metal-metal motor, because the high torque (rubbers) stator for positive displacement motors, available in Brazil do not work over 300 °F.
In order to overcome all of these challenges and optimize the cutting process, tests were performed before the job in a similar Cr-22 tubing sample, using a standard two blades pipe cutter attached to a 2-1/8" metal-metal motor. After the failure in the first test, improvements in the pipe cutter were done until reaching an effective cutting system.
This paper presents in details all steps in the pipe cutter design development and summarizes the operational procedures executed in this successful job using 1-1/4 inch coiled tubing, metal-metal motor and optimized pipe cutter.
It will be of value to point out other (more expensive) options that the customer normally would have had to use, i.e. snubbing unit with spaghetti pipe.