Actively-producing large high pressure, high temperature (HPHT) wells around the world are increasingly scarce. These wells are complex and costly due to the large, independent, jacket-based operations needed to exploit reserves. So now attention is shifting towards small to medium-sized HPHT developments which can produce to a dedicated floating facility.
But handling HPHT operations safely, economically, and with environmental sensitivity, calls for highly specialised equipment and technology to exploit reserves. So what’s the most suitable engineering match for these wells?
Jack-ups: the ideal fit
Semi-submersible mobile units have traditionally been used to perform drilling, completion, intervention and abandonment services on subsea wells. However, compared to semi-subs, heavy duty jack-up drilling units rated to 150m water depths, can now undertake such activities at reduced cost and risk when a jack-up deployed high pressure drilling riser is used to span the gap between a dry surface BOP and a wet subsea tree.
An additional benefit of jack-ups is the possibility for improved wellhead/low pressure housing/subsea tree loading performance. Top tensioned drilling risers and lower jack-up rig offsets incur less load and fatigue damage on the wellhead. This extends the service life of equipment, improving safety margins and operational envelopes.
Moreover, typical high pressure drilling riser systems are designed to withstand 50-year storm conditions. Unlike semi-submersibles, jack-up rigs remove the need to disconnect from the well in extreme weather conditions, eliminating unexpected downtime.
As new generation jack-ups are now capable of operating in increasing water depths, the scope of subsea wells viable for a jack-up deployed high pressure riser system is also increasing.
Dual barrier riser systems: a perfect partner
A good example of this type of approach is our light-weight, dual barrier HPHT drilling riser system, , which offers a cost-efficient alternative to semi-submersible installation. This enables an inner riser string to be installed inside a conventional high pressure drilling riser to provide full 20,000 psi capability, without compromising safety, integrity or operational performance.
Traditionally, at pressures of around 10,000 psi and elevated temperatures in excess of 121oC, the required material composition, available manufacturing techniques and capital cost of large bore HPHT steel riser could become prohibitive. This has limited the advancement of high pressure drilling riser deployments to lower temperature and pressure projects due to the technical and commercial restrictions.
However now, our joint solution facilitates safe and effective drilling operations in HPHT conditions and provides a structurally sound, pressure retaining conduit between the subsea wellhead/tree and the rig’s surface BOP.
Our engineers developed the first high pressure drilling riser systems deployed in the North Sea in the 1990s, which were typically used on lower pressure wells. This expertise feeds into the design of our dual barrier riser system. With increased well pressure requirements over 5,000 psi and for those above 10,000 psi, this system can offer significant safety benefits, reduce rig time and increase savings over single barrier systems.
Want to know more about our advanced drilling riser systems? Find out more here.