Subsea riser systems – taking the pressure off HPHT developments - Aquaterra Energy

Subsea riser systems – taking the pressure off HPHT developments

High pressure, high temperature (HPHT) developments offer new opportunities in mature basins – but they invariably pose safety, technical, cost and environmental challenges. Ben Cannell, Innovation Director at Aquaterra Energy, looks at how a subsea riser system can take the heat out of the process….

HPHT is not fully defined within the industry: conventionally it’s a well pressure level of over 10,000psi, with an ‘extreme’ bracket of over 15,000psi. Although not fully defined, this challenging operating environment and price uncertainty means reliable, cost-effective solutions are more important than ever. Of course, as the North Sea adjusts to the lower oil price, we expect to see some HPHT developments to be progressed and others put on hold.

One example of a notable HPHT development is the Culzean development, which began production in June 2019: the largest gas project to be sanctioned in the UK in the last 25 years. However, UK government departments and industry remain keen to push HPHT developments, and there is certainly a prize to pursue, where subsea riser systems can help you to be a winner.

Finding a ‘keeper’

Converting an HPHT exploration well into a producer doesn’t come without its challenges - failure of mudline hangar systems, as the extreme pressures and temperatures impose very high loads on the systems, as an example.

An HPHT exploration well isn’t a small undertaking – broadly speaking, deploying a jack-up rig to drill a HPHT well today costs in the region of £70million and many times more for the same well using a semi-submersible – so it makes sense to make it a ‘keeper’. The question is: how?

Say we’re talking about a well in the conventional HPHT range rather than installing a mudline system with an exploration wellhead system at surface – with no use once complete – operators could look to install a subsea wellhead and deploy a subsea riser system from a jack-up rig to facilitate the campaign. The tie-back of subsea wellheads to a platform jacket with a dry tree is a proven concept in the North Sea and elsewhere.


While this package can’t work for every subsea wellhead and jack-up facilitated risers it could save millions of pounds over the long term, it can also:

  • Eliminate the failure risks associated with the mudline hangar systems
  • Manage pressure drilling (MPD) technology that can be brought in to offset other technical issues
  • Maintain a tighter more controlled drilling mud pressure
  • Use metal-to-metal for gas tight seals, addressing the risk of leaks

The technology has been commonly used on jack-ups for some years in conjunction with subsea riser systems.

Changing the industry’s mindset

The proposition does call for a change in industry mindset, but these changes can bring about great benefits.

At Aquaterra Energy, we want to be part of that process. It’s still a niche market, but we’re introducing to the market an HPHT subsea riser system that can work on wells up to 15,000psi.

Most jack-up well campaigns we have worked on to date have involved pressures of under 10,000psi but it’s undoubtedly a time of change. Whereas our subsea riser systems work on the new ‘normal’ of between 5,000 and 10,000psi.

Over the past year or so, however, we have experienced a marked rise in inquiries related to wells up to 15,000psi. However, the changing market landscape may mean that only the most economically viable wells can be pushed forward – which is why our approach is key.

But if there is a viable way to turn an exploration or appraisal well into a ‘keeper’, perhaps HPHT developments can continue to progress during this lower oil price period. Get in touch to hear more about this our new HPHT subsea riser system.