Pipeline Routing and Engineering for Ultra-Deepwater Developments
Authors: Bonnell Simon A. , Blackmore Malcolm S. , Tam Christophe K.W. 
Published: October 2008

As oil and gas explorations venture into deeper water and more hostile, "frontier" subsea conditions, pipeline routing and engineering activities become more critical to the planning and realization of these projects. Of particular importance is the requirement that survey and engineering activities are planned and started early, to ensure that a complete technical and economic model can be established at the outset and that risks are well understood and managed. This paper provides an overview of the governing issues relating to the successful execution of route planning and surveys for ultra-deepwater pipeline projects. It includes the importance of desktop studies, the planning and execution of surveys, the selection of survey techniques and equipment, and "semi-real time" engineering activities performed onboard the survey vessel. The use of Limit State Design concepts is also briefly discussed.

Introduction

Recent advances in technology, combined with the new building or upgrade of construction equipment, are resulting in the installation of rigid steel pipelines in ever increasing water depths. Examples of recent deepwater pipelines include the 12-in. Shell Mensa pipeline, installed in approximately 1,500m by the S-Lay method, and the 10-in. Petrobras Roncador pipeline installed in approximately 1,300m by the reel method. Exceeding these depths is technically feasible by the J-Lay method, the technique currently being considered for installation of several deepwater pipelines in the Gulf of Mexico, and the Blue Stream pipeline crossing the Black Sea in approximately 2,100m water depth.

While this may be the case for a mature region such as the Gulf of Mexico, the technical challenge can differ when considering ultra-deepwater applications in remote regions, and regions where other influences such as tectonics, exist. In such cases, the technical challenge of finding a suitable route for the pipeline may be as great, if not greater, than that of actually installing the pipeline on the seabed. Examples of such projects are the Oman to India and the Blue Stream (Black Sea Crossing) pipelines.

This paper provides an overview of the governing issues relating to the successful execution of route planning and surveys for ultra-deepwater pipeline projects. Topics that are discussed include the importance of routing, desktop studies, the planning and execution of surveys, the selection of survey techniques and equipment, and "semi-real time" engineering activities performed onboard the survey vessel. The paper also discusses the relevance of limit state design for ultradeepwater pipelines.

Within the context of this paper, the terms ultra-deepwater and large-diameter are defined as water depths greater than 2,000m and outer diameter greater than 16-in respectively.

The Importance of Routing for Ultra-deepwater Pipelines

Route selection is a balance between minimizing the length of the line and the avoidance of potential hazards; where length adds cost and hazards increase risk and also add cost where interventions are required.