Claxton Engineering enjoys a fine reputation for coming up with highly effective engineering solutions, often within very tight deadlines.
The company is strongly inclined towards practical and reliable designs, but at the same time is not afraid to challenge conventional thinking.
You look at some solutions and they are so elegant, so simple, that you wonder why nobody has thought of them before. Claxton’s retractable riser guide arms are a perfect example of this. The retractable arms enable drilling or workover risers to be run and landed safely and reliably on subsea wells; they also save rig time and render the whole process reasonably independent of the weather.
But any normal guide arms would do this – what is the advantage of the arms being retractable? The problem is that to fit over the standard guide posts fitted to subsea wells, the fixed arms need to extend about 6 ft from the riser, and so they are incapable of passing through the rotary table of even the biggest jackup drilling rigs. It is therefore normal practice to fit the arms to the riser below the rig floor – maybe on the Texas deck, if the rig has one. But this is not always easy owing to limited access or restrictions on the span of the structure to be fitted. Indeed, on modern jackups the presence of pollution containment units below the rig floor makes the task almost impossible. Then it is sometimes necessary to feed the riser into the rig from a boat stationed below it – with obvious economic and operational implications.
It takes a lateral thinker to challenge the basic assumptions in life – in this case that the guide arms cannot pass through the rotary table. Dannie Claxton is one such thinker. He says, “It was ConocoPhillips who asked us to re-evaluate this problem, and when we got talking it just seemed such an obvious solution to make the arms retractable, so avoiding having to undertake any work at all below the rig floor. The design is relatively straightforward, and we were able to engineer the guide arms, manufacture them and fit them to the stress joint on ConocoPhillips’ chosen riser in the three weeks before the operator proposed deploying it in the North Sea.”
In fact, because of a late change of plan, the operator was able to give Claxton more time to fine-tune the design. The arms were quickly fitted with more powerful hydraulic cylinders than initially specified, and the design of the guide cones that engage with the Regan connector on the guide post was improved. The riser has now been successfully deployed from the Maersk Inspirer drilling rig to workover the ConocoPhillips M08 subsea well, still in the North Sea.
Doubtless, the North Sea has seen far more impressive feats of engineering; however, there cannot be many that possess the payback potential of this relatively modest but genuine engineering solution.