SIIBED: Subsea Ice Interaction Barriers to Energy Development – Overview

Abstract

The objective of this paper is to provide an overview of the Subsea Ice Interaction Barriers to Energy Development (SIIBED) project including work on acceptance criteria used in finite element analysis (FEA), physical modelling and risk analysis activities. The overall structure of the SIIBED program and the relationship between the various tasks is presented. SIIBED is a continuation of two previous projects funded by Energy Research & Innovation Newfoundland and Labrador (ERINL): Alternatives to Flowline Trenching (AFT) and Alternatives to Weak Links (AWL). The SIIBED scope was expanded to include subsea cables, reflecting the interest in moving towards electrification of offshore operations. Numerical modelling of iceberg interaction with rigid pipelines, flexible flowlines and cables requires an understanding of elastic/plastic stiffness and stress/deformation limit states. This paper reviews existing technologies, industry standards and best practices. The behavior of rigid pipes in an ice grounding environment is fairly well understood and was reviewed in relation to applications supporting developments in the Beaufort Sea. In contrast, the construction of flexible flowlines is much more complex and variable, and firm guidelines on design strain limits are lacking for the application considered here. Subsea cables are even less well understood. When considering subsea cables and the adoption of limit state design criteria, the model of failure consequences was examined in the context of approximately a 15 second ice-pipe-soil interaction before the iceberg passes over-top. Under loading, the three conductors in an AC cable must maintain separation to prevent electrical arcing. Insulation around a single conductor DC cable must remain intact. It has been observed that, unlike steel pipes that ovalize when compressed restricting access for pigging as well as loss of strength integrity, the cables (particularly the insulation around conductors), bounce back to the original shape. The potential loss of conductivity could not be tested. If cables bounce back, then to prevent arcing, a cable could be de-energized for the short period ice keel interaction and re-energized after the iceberg passes over-top. While a considerable understanding for modeling rigid pipelines against iceberg keel interaction exists, analysis of subsea cables is much less understood. These are, however, now necessary as the oil and gas industry transitions to a net zero carbon footprint or alternative energy sources (e.g. offshore wind power) are developed in ice prone regions. While more testing and verification work is needed, this work suggests that requirements for protecting rigid pipelines may not be appropriate for electrification cables, possibly too, flexible flowlines.