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.