It was no surprise that Offshore Europe this year was once again jam-packed with new and trusted technologies being applied in the North Sea and abroad. The Aberdeen, Scotland, event was well-attended, and the options for things to see were many.
One of the more interesting technologies was exhibited by a hometown company, Aberdeen-based Deep Casing Tools, which had on display its new Turborunner. The turbine-based tool is designed as a high-speed reaming system that enables completions to be landed at target depths, especially in areas like the Saxon field in the Central North Sea, where borehole stability can be a significant challenge due to the occurrence of interbedded shale layers.
In addition, horizontal openhole sections often are interspersed with reactive and collapsing clay layers. These conditions combine to provide a very challenging environment for landing production liner at TD.
In a recent project, there were problems with a planned well design that involved drilling an 8 ½-in. hole from a semisubmersible, then running a 7 5/ 8 -in. predrilled liner 1,000 m (3,000 ft) horizontally to 2,650 m (8,700 ft) TD. This proved difficult, and the completions team opted to sidetrack the well with a larger 9 ½-in. horizontal drain to give a new predrilled liner a better chance of reaching TD. String rotation was not an option due to the limited torsional yield strength of the flush joint connections being used. A single-run PDM motor also was not viable due to the risk of a pressure spike on stalling or starting, which could set the liner prematurely. The Turborunner made sense because the standpipe pressure actually drops as the tool is loaded or stalls, which proved to be a significant operational advantage. The tool was used to wash and ream the liner to target depth within a 12-hour period. It recovered 1,000 m of open hole, accessing 530 m (1,750 ft) of net pay. It was operated at circulation rates up to 7 BPM, with 400 psi across the tool and a standpipe pressure of 900 psi. The tool’s unique design combines high-speed rotational reaming with very low operating pressures. The turbine design allows RPM to slow and even stall without any reactive mechanical torque, nor does it cause uncontrollable pressure spikes. The reamer shoe is the only part that rotates, so the completion string and any complex completion equipment remain stationary with a need to rotate. In theory, this tool operates as if there was a drill bit on the end of the completion string. In many cases, it could provide the best technical shot in landing difficult completion strings. This tool has been used primarily offshore, but it will most likely debut in land developments very soon.