Design, Operations Planning and Experience From the Marine Operations for the Europipe Jacket With Bucket Foundations
Authors: Rusaas P. , Giske S.R. , Barrett G. , Marine Aker , Christiansen P.E. , Baerheim M. 
Published: October 2008

The Europipe 16/11-E riser platform was successfully installed in the Norwegian part of the North Sea last summer. Rather than having the traditional piled foundations, the platform has bucket foundations consisting of one inverted 12m diameter bucket in each of the four Jacket comers, After set down of the Jacket on the seabed and self weight penetration, the Jacket legs were water filled and the buckets thus gained further penetration. Finally suction within the buckets penetrated them to target enetration.

This paper describes the preparatory work and the installation of the structure, discusses the main problem areas and experiences gained from the installation.

INTRODUCTION

The transportation, installation and suction penetration of the Europipe Jacket completed placement of the world's first ever steel Jacket with bucket foundations

The Europipe Jacket is basically a four leg lift installed structure of standard North Sea service design. Jacket particularities are:Cross braced legsTwin crane lift installedMain dimensions 20m × 20m at the top elevation40m × 40m at mudline elevation101m overall heightFour 012m buckets with overall height 9.5m, target penetration 6.0mTwo 030" water evacuation valves at top of each bucket

The Jacket was installed by the semi submersible crane vessel Micoperi 7000 (M7000) in a water depth of70m (230ft). The hook loads, as measured by the M7000 crane load cells, were totally 5240t. Adjacent to the Jacket is the 16/11-S riser platform. The two platforms were interconnected by a 79.5m long bridge.

Installing a jacket with bucket foundations revealed new challenges as special methods and equipment were required.

PREPARATORY WORK

The potential of the bucket design

A critical parameter when installing a jacket offshore is the length of the weather window required for the part of the operation between safe conditions, i.e. the period from start of cutting sea fastening until necessary on-bottom stability has been achieved. Bucket foundations are superior to the piled foundation solution as it gives better on-bottom stability immediately after set-down. The Europipe Jacket could survive the 10 year summer storm (Hmax = 13.2m) immediately after set-down, and the 100 year storm shortly after the suction operation had started.

The bucket solution will only be superior when the shorter installation period is fully recognized by the Installation Contractor. The installation period of the Europipe Jacket was probably shortened by some 3to 4 days due to the bucket foundation solution. Additionally some 2-3000t of pile material would be required for piled foundations.

The challenge to set and secure a jacket with bucket foundations

It was identified at an early stage in the project thatthe installation of the Jacket would be different inkey areas from the norm for a typical North Sea type of crane installed Jacket. The major challenges can be summarized as follows:The Jacket must be kept in hover position and set down in such a manner that the seabed would have minimum disturbance. Channels or rabbit holes in the sand around the circumference of the skirts.