The Culzean field was discovered in 2008 and is one of the largest fields in the British North Sea. Ramboll is providing detailed design of three jacket structures for the field, which has the potential to meet around 5 per cent of the UK’s gas demand in 2020/21.
Maersk Oil operates the High Pressure/High Temperature (HP/HT) Culzean field, located 242 km (145 mi) off the coast of Aberdeen. The Culzean field is Maersk Oil’s first operated ultra-HT/HP gas development. Its reservoirs are confirmed at an average depth of app 4.5 km (14.763 ft), within the target reservoirs of Triassic and Jurassic age.
A platform for HP/HT field
With temperatures reaching 170 degrees C (338 degrees F) and the pressure being three times higher than average fields, a platform optimised for these conditions is paramount. The overall Culzean concept development consists of a wellhead platform (WHP), a central processing facility platform (CPF), and a separate utilities and living quarters (ULQ) platform. The platforms will be linked via two bridges approx. 100 m (109 yd) in length.
A prestigious two-step project for Ramboll
In 2014, Ramboll was awarded the detailed design for the Culzean wellhead platform (WHP) jacket, associated piles and appurtenances. The detailed design included all primary installation aids, e.g. sling platforms, working platforms, spreader bars etc. including detailed design of all required sea-fastening.
A significant part of the project work in the early phase was an evaluation of the FEED design and further improvements of the FEED design with respect to pile/soil interaction, transportation and lifting arrangement. Ramboll worked in close collaboration with the client to ensure the optimum design. Moreover, Ramboll acted on all comments from certifying agency, installation contractor and marine warranty surveyor reviews, and updated documentation and drawings accordingly.
In late 2014, after successful completion of the detailed design of the WHP jacket, Ramboll was awarded the detailed design of the jackets for both the CPF platform and the ULQ platform.
4-legged twisted base jacket structure for the WHP
The wellhead jacket will be a 4-legged, twisted base jacket structure in some 90 m (300 ft) of water, able to support a 8000 mT topsides. The jacket must facilitate access from a drilling Heavy Duty Jack-Up.
The platform concept required 14 well slots for 30" conductors and a 24" drain caisson. The foundation consists of 12 96" piles with a target penetration depth at 45 m (150 ft). The design was carried out in accordance with BS/EN/ISO 19902 and client specifications.
The jacket was designed to resist load impact from sea transportation, i.e. detailed motion analyses were carried out and the fatigue damage during transportation was taken into account. The jacket will be transported in horisontal position and lifted and upended by means of a heavy lift vessel. The expected lift weight is approx. 7000 tonnes. To minimise the installed "out-of-vertical", the jacket will be installed on preinstalled under-leg piles. The design included detailed design of a template and the under-leg piles. Detailed finite element analyses were carried out for multiplanar joints and pile sleeve clusters.