Engineers Australia

Design and Installation of Mobile Offshore Drilling Unit Mooring Piles Using Innovative Drive-Drill-Drive TechniquesBest paper (High commendation) from the 13th ANZ Conference on Geomechanics, Perth 2019

Ian Finnie, Rick Gillinder, Mark Richardson, Carl Erbrich, Mark Wilson, Fiona Chow, Meysam Banimahd and Steve Tyler

Abstract

The North West Shelf, which is Australia’s largest offshore oil and gas province, is well known for the engineering challenges posed by the calcareous seabed sediments present and its exposure to extreme weather associated with tropical cyclones. Mobile and fixed platforms are used to tap into the hydrocarbon reserves and these need to be secured to the seabed using substantial foundations and anchors, which must resist onerous cyclic loads. This paper describes a project where an innovative drive-drill-drive installation approach was adopted to enable the installation of twenty-four anchor piles to moor a mobile offshore drilling unit (MODU) at two drilling sites. The two sites encompassed a wide range of complex seabed geologies, from high strength limestones to uncemented silts, where conventional drag anchors or driven anchor piles would not prove entirely suitable. Installation was carried out using a dynamically-positioned vessel, oper- ated by Fugro, on which an inventive purpose-built drilling tower had been erected specifically for the project. The in- stallation also included development and deployment of an ingenious seabed frame that could grip and release the piles progressively, plus casings to temporarily stabilise the drilled holes from collapsing sands. This project provides an ex- cellent example of how multidisciplinary collaboration can embrace innovative solutions to successfully deliver complex projects safely, on budget and to an accelerated schedule.