This paper describes a coiled tubing milling operation using fiber optic enabled coiled tubing and downhole tools for real time depth control and downhole monitoring of critical parameters. A description of the technology used, the job design, tool selection and execution of the job, the challenges encountered during the operation and the successful outcome are presented and discussed in the paper. The case history presented in this paper marks the first time that this particular fiber optic technology had been applied during a milling job worldwide.
Coiled tubing milling operations can be challenging when precise depth measurement is critical. For the case history discussed in this paper the operator needed access to the production liner below the end of tubing with a BHA with a larger outside diameter than the inside diameter of the nipple installed in the tail pipe of the tubing. It was necessary to mill out this nipple profile while ensuring that other completion accessories above the nipple, including the production packer, were not inadvertently milled or damaged. Therefore, accurate depth control during the milling process was essential.
Depth control was obtained with the real-time fiber optic CCL measurements. In addition, real-time pressure and temperature measurements were available from the fiber optic enabled BHA to monitor the milling parameters.
The latest fiber-optic technology for coiled tubing including modules for CCL, temperature and pressure was used for the first time during a milling job. The data recorded, transmitted and integrated with the data acquisition software, created the ability to customize and optimize well intervention in realtime, and ensured that the required depth control precision was obtained, with precise control on the downhole milling parameters to optimize the milling operation.