Offshore pipeline protection against seabed gouging by ice: An overview

Abstract

Offshore operators in the Arctic will rely on seafloor installations, notably pipelines, to manage and transport hydrocarbons. In icy waters, these structures are at risk of being damaged by gouging ice features, either icebergs or sea ice ridges. This phenomenon generally occurs when an ice feature drifts into shallower areas and its keel starts plowing the seabed over considerable distances. It is generally agreed that adequate protection against these events can be achieved by burying the pipeline below the seafloor. The question is: what constitutes a safe and economical burial depth for any given location? An answer to this question requires adequate knowledge of material properties (soil, ice keel and pipeline), a reliable handle on the processes taking place during gouging and a consensus on what constitutes acceptable risks. Research on this subject has been on-going for the past few decades, along several fronts. One is by means of field studies, including replicating gouging scenarios in a natural environment, in situ ice characterization, seabed mapping and on-land relict gouge investigations. Another is through laboratory studies, either at single gravity or in a centrifuge. Theoretical analyses and numerical simulations have also contributed to our current understanding of gouging phenomena. Several research groups proposed some form of guidelines for estimating gouging parameters—examples are presented. These methodologies are instructive in that they represent an integrated approach to an improved understanding of gouging phenomena. They point the way to what one may expect in terms of future guidelines to a safe and cost-effective burial depth. ► Sub-sea pipelines are an effective tool to transport oil and gas from offshore sites. ► In cold regions, these pipelines can be damaged by seabed gouging ice features. ► Protection from these events can be achieved by burying them below the seafloor. ► Field, laboratory, numerical studies help define safe and economical burial depths. ► Methodologies are proposed to guide pipeline design in gouge-prone waters.