Novel Design and Installation Issues on the SOEP Offshore Gathering and Interfield Pipelines
Authors: Draaisma Sil , Lamison Craig , Stewart Hugh R. 
Published: October 2008

The Sable Offshore Energy Project (SOEP) 26" offshore gathering line and the associated interfield lines are the first major offshore pipelines on the East Coast of Canada. The benefits of early cooperation betweeen Owner, Designer and Installer are discussed with opportunities for some interesting synergies arising from parallel engineering and planning of installation. The sea states and seafloor conditions around Sable Island impose some substantial loading considerations which resulted in some novel design and installation solutions. These are described together with some of the novel cathodic protection considerations used on the project. Some interesting certification and regulatory challenges encountered in progressing with the pipeline are also described. Vessel and equipment selection at an early stage permitted some unique and complimentary design and installation methodologies. The state of the art welding and automatic ultrasonic testing approach and its beneficial impact on production lay rates will be reviewed.

Introduction

Interest in the Nova Scotian offshore was revitalized in 1995 after being postponed during the mid 1980s. SOEP consists of a six field natural gas development commencing with three fields in the initial development referred to as Tier 1. The Thebaud field, where the central processing platform is installed, is west of Sable Island and is connected to the Venture and North Triumph fields which are located to the east and south east respectively. Interfield lines connect satellite platforms at these locations to Thebaud where the gas is dried prior to be transported ashore through the 26" trunk line. (Figure 1: Plan Overview). Prior to project approval by the Owners in early 1998, the project went through a lengthy regulatory process. The regulatory requirements which involved satisfying several regulatory bodies with overlapping jurisdictions continued past sanction and required considerable additional effort to maintain compliance. However significant cooperation between regulators, certifying authority and the project did allow equivalent deviations from applicable codes without jeopardising safety or asset integrity.

Novel Aspects of SOEP Pipelines

Many of the aspects of the SOEP pipeline are fairly traditional, although the project is unique in being the first offshore petroleum gathering system in Canada. However there are several aspects that are novel and may be applicable to pipelines in other locations or future pipelines offshore Eastern Canada and USA. These aspects are:buckle arrestor solution,trench requirements and trenching processinstallation vessel selection and obtained lay rates-automatic UT and weld defect assessmentanode sled - corrosion protection,expansion loop within Venture jacket,

A description of these aspects are interwoven into the following summary of the Project.

Project Criteria

Several project criteria were determined by the Owners and documented in a Design Basis Memorandum. Many of these criteria were developed in conjunction with the designers and installers. For instance the design life of 25 years was evaluated in comparison to a 40 year design life. Fatigue, often the determining factor in assessing structure life, did not govern as operational strategies were considered to limit unacceptable spans.