Design, Fabrication, And Installation Of The Auger Tlp Foundation System
Authors: Ulbricht W.R. , Ripping M.A. , Doyle E.H. , Stevens J.W. , Mayfield J.G. 
Published: October 2008

The Auger Tension Leg Platform (TLP) is held on location with twelve steel tubular tendons mechanically latched in groups of three each to four individual foundation templates precisely positioned on the sea floor in record water depths. Each template is secured with four piles driven into the sea floor and mechanically swaged into the template guide sleeves.

This paper overviews the major facets in the design, fabrication and installation of the foundation templates and piles that comprise the Auger TLP Foundation System. Design considerations discussed include structural detailing to suit fatigue, mechanical interface requirements, and tension pile effects. Although the template fabrication was conventional, dimensional control, weight/center of gravity control, and testing of mechanical system interfaces were essential to the success of the installation.

Extensive installation engineering and planning were conducted, including the development of several purpose-built installation aids. An overview of the sequence of field operations to lower and accurately position each template, run and stab piles in each corner sleeve, drive piles to grade with an underwater hammer, and finally swage each pile into structural load carrying grooves in the template guide sleeves is presented. Contingency plans and procedures prepared to deal with precise position and level tolerances are discussed. The descriptions of the field operations highlight the methods that were used to adapt existing construction vessels and equipment to work effectively and reliably in the deepest water yet attempted for a TLP installation.

INTRODUCTION

Shell Offshore Inc. 's Auger Tension Leg Platform is located in the Gulf of Mexico in Garden Banks Block 426 at a nominal water depth of 2860 feet. Particulars of the four foundation templates and sixteen piles are as follows:

Templates

Dimensions 60 feet × 60 feet × 48 feet (L × Wx H)

Weight (dry) 611 s. tons

Piles

Dimensions 72 inch 0.0. × 427 feet

Weight (dry) 203 s. tons

Contracts for the fabrication and installation of the templates and piles were awarded in March, 1992 to Aker-Gulf Marine of Ingleside, Texas, and HeereMac v.o.f. of Leiden, The Netherlands, respectively. Fabrication was completed late November, 1992, and installation completed late December, 1992.

Design

Three tendons per corner are attached to each independently placed foundation template. An isometric view of the template is shown in Figure 1. A view of the seafloor elliptical well pattern and the foundation templates during installation operations is shown in Figure 3. The template tendon receptacles are located such that the tendons hang vertically when the TLP hull is centrally located over the well pattern. Each foundation template transfers tendon loads to four 72-inch diameter, vertical piles driven to a penetration of 374 feet below the mudline.

Load cases

The load cases and design safety factors are shown in Table 1. The direction of load application was assumed from 0° to 360° in 22.5° increments.