Angostura Phase 3 flowline Stability – FEED

Background

Located 22 miles off the east coast of Trinidad, BHP Billiton’s Phase 3 development of the Angostura field (AP3) includes a 6.2 mile long 12-inch flowline from the Angostura West drill centre to a tie-in spool at the base of Angostura gas export platform. The flowline route comprises a large curved section of about 3.1 mile with water depth varying between 100 feet and 164 feet.

The AP3 stability solution developed during the FEED phase considered metocean criteria from previous phases of the project and recommended installation of 124 concrete mattresses at a significant cost to the project. BHP Billiton engaged Atteris to re-evaluate the FEED design (performed by others) with a view to minimise the requirement for secondary stabilisation.

Work Performed by Atteris

Atteris managed the generation of revised metocean data specific to the Phase 3 pipeline route, and based on this data performed a 3D stability analysis in accordance with DNV-RP-F109 to assess the stability of the flowline.

Atteris’ in-house and DNV verified stability software CORUS-3D was used to perform the analysis. The analysis considered the effect of random sea states, and assessed the lateral displacement of the flowline, stresses and tensions in flowline, and potential movement at the flowline end termination location.

Based on the findings of the 3D analysis, it was concluded that the flowline, has adequate self-stability for the design metocean conditions. The FEED design requirements for secondary stabilisation were reduced accordingly.

Benefits

A bespoke approach to flowline stability design eliminated the requirement to install 124 concrete mattresses for secondary stabilisation as originally proposed by the FEED engineering consultant.