The advantages of using jack-ups for subsea drilling

For projects involving shallow water drilling in the North Sea, an appropriately equipped jack-up rig may be a better fit for the task than a semi-submersible rig.

When developing shallow water subsea projects, most people in the oil & gas industry will instinctively assume that a semi-submersible rig should be used for the purpose. But this is not the only viable option. In fact, a jack-up using high-pressure risers can be even better suited for the purpose under certain conditions, such as those found in the North Sea.

The main reasons for considering a jack-up rig for subsea drilling are:

Reduced downtime waiting on weather
A harsh or ultra-harsh environment jack-up with high-pressure riser systems can be used in extreme weather, even in storm conditions you only meet every 50 years in the North Sea. By contrast, a semi-submersible is likely to have significantly more downtime due to harsh weather.
Improved equipment lifetime
All rig types will transfer motion generated by weather and sea currents to the subsea well. However, a semi-submersible rig will move around more, even during benign conditions, causing wear on critical subsea well equipment. On the other hand, a jack-up with a high-pressure riser provides a more stable system that can significantly reduce fatigue damage to the equipment.
Additional operational benefits
Using a jack-up rig will typically reduce loading on surface and subsea components, and tree handling and installation can also be completed from a jack-up.
Potential cost and emissions upsides
Fuel consumption on a jack-up is typically lower than on a semi-submersible rig, leading to a more attractive operational cost picture which also translates into fewer CO₂ emissions. In jurisdictions imposing a CO₂ tax, this provides an additional cost upside on top of the more responsible emissions profile.

Maersk Drilling has a proven track record of subsea drilling using jack-up rigs, having completed more than 30 jack-up subsea operations in the North Sea.

One example is Maersk Interceptor which in 2018 conducted a highly successful three-well subsea campaign in Norway for Spirit Energy, completing the work 68 days ahead of schedule. Read more about the case and why it was such a success here.