Bayu-Undan Substructure Foundations: Conception, Design & Installation Aspects
Authors: Sims M.A. , Smith B.J.A. , Reed T . 
Published: October 2008

The substructures for the two Bayu-Undan processing platforms were successfully installed in the mid 2002, and the floatover decks in the third quarter of 2003. This paper describes the shallow foundation scheme and design and installation aspects adopted for the substructures for the platforms, the circumstances which led to the conception of the novel foundation system and the challenges that were overcome during design to ensure feasibility of the installation of the substructures.

Introduction

The Bayu-Undan field is located approximately 500 km northwest of Darwin, Australia and 250 km east of the Democratic Republic of Timor-Leste (formerly East Timor) in an area known currently as the Joint Petroleum Development Area (JPDA - formerly the Zone of Cooperation between East Timor and Australia). The field contains 2.7 TCF of recoverable gas reserves and roughly 375 million barrels of condensate and LPG. The development lies in 80m of water and is operated by ConocoPhillips with Eni, Santos, INPEX, Tokyo Electric Power Company, and Tokyo Gas Company as co-venturers. The first phase of development, approved in August 2000, focuses on gas recycling with condensate and LPG recovery. The field facilities consist of:A Drilling, Production, and Processing (DPP) platform (with a dry topsides weight of 14,000t)A Compression, Utilities, and Quarters (CUQ) platform (with a dry topsides weight of 11,500t)A flare bridge and cantilevered flare tower connected to the DPPA single wellhead platform (WP1) located 7.4 km east of the two main central processing platforms(CPP)A 172,500 dwt FSO that stores and offloads condensate, propane, and butane as separate products The field is set to come onstream early in 2004 with full production of 1.1 BCFD of rich gas and 115,000 BPD of liquids anticipated mid year.

Phase II of the project, which was approved in June 2003, involves building a 26" gas export pipeline to Darwin to feed a 3.52 mtpa LNG plant scheduled for start-up in early 2006. The infield development was designed by TIGA, a joint venture between Worley Pty Ltd and Fluor Daniel Pty Ltd.

The CPP Platforms - DPP Platform Floatover Just Completed(Available in full paper)

Design of the Bayu-Undan foundations proved to be a very challenging aspect of the project due to the remote location and the geotechnical properties of the calcareous soils in this region of the world.

The conventional method of providing foundation fixity to substructures installed on calcareous material in Australian waters is by means of drilled and grouted piles. This is time consuming for the offshore installation spread and consequently very costly. It is also fraught with the risk of additional cost due to grout loss and hole collapse due to the variable nature of the calcarenite. Two major platforms off the North West shelf of Western Australia have required extensive foundation remedial works. The two Bayu-Undan Central Processing Platforms are relatively unique in that they have heavy topsides, 'squat' 8 legged steel framed jackets configured for deck floatover (see Figure 1), low environmental loading, medium water depth of 80m and are located on a substrata consisting of 2m of silty sand overlying a hard caprock.