REBUILDING the remaining Thistle drilling package was not easy, nor was it ever likely to be, given that it had stood idle for 20 years in a marine environment.
“It was left in quite a poor state,” said Alisdair Young, who took over management of the project when it was about two-thirds complete.
“Our engineering arm, RDS, had a full study into what would be required to reactivate the package.
“Clearly, with an installation as old as Thistle, every time we dug deeper, we found more problems and, as a consequence, costs escalated.
“I think we had a lot of heartache at the beginning, but once we got to the later stages of decommissioning the equipment and reinstallation of systems that had been refurbished, then it became easier and things went well from then on.”
Of the original drilling package, what percentage of the beast had to rebuilt?
A very high percentage of existing pipework and beams had to be replaced. Indeed, most things from the “ground” up, except for the basic structure, although the original frame had to be strengthened to accept a top-drive unit, which replaced the original Kelly system.
There were very few (drilling related) systems on Thistle that weren’t overhauled. In a nutshell, the chassis remained because it was basically in reasonable shape. But all the rotating equipment has been replaced. One of the problems of taking a first-generation North Sea drilling package and trying to bring it into the 21st century is the lack of space available, especially for modern automated pipe-handling systems. Such old-style taper derricks simply do not compare with today’s “square” derrick.
“Fourth-generation systems used in the UK wouldn’t actually fit within the footprint of Thistle, so while we have improved mechanical handling … certain things we would have liked to do could not be done because of space restrictions,” said Young.
“However, importantly, the top-drive allows us to drill more efficiently; there’s less exposure to personnel when handling tubulars; it’s better for directional control, and it will be a lot more flexible than the old Kelly system.”
Drilling manager Simon Richards added: “Essentially, we’ve reinstated what was there, but with a top-drive. The deepest well on Thistle now is about 17,500ft. We’ve designed the rebuilt drilling package to go re-drill a well of that sort.
“Whether we can attempt something much more than that, I think we probably have limited scope to go a long way beyond that. We would need to look at a further upgrade if we really wanted to go to extended reach. We can cove the whole of the existing field … Thistle and Deveron. What we can’t do is go near-field exploring by using extended reach. That’s not possible even with the capability that we have today.”
For Young and the KCA Deutag team of 70 or so engineers and other specialists involved with Thistle, the good news is that they get to run the drilling package that they devoted so much effort to restoring.
“It’s a big deal for KCA Deutag, working with Lundin (UK asset now run through EnQuest JV) and proving that we can deliver effective and safe operations for the client,” said Young.
“And it’s a big deal for me personally as I worked on Thistle in the early-1980s, and coming back to manage Thistle in this way is not something I had every imagined doing.
“When you say we’ve just started drilling again on Thistle, you get replies like, ‘Good heavens, I was on Thistle back in the ’70s’. It is remarkable how many people have been associated with Thistle over the years.”