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Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Prepared For: BSEE Doc Ref: 100100.01.PL.REP.004 Rev: 0 Date: July 2015

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Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Prepared For: BSEE Doc Ref: 100100.01.PL.REP.004 Rev: 0 Date: July 2015 Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Prepared for: BSEE Doc Ref: 100100.01.PL.REP.004 Rev: 0 Date: July 2015 Final Report This final report has been reviewed by the Bureau of Safety and Environmental Enforcement (BSEE) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the BSEE, nor does mention of the trade names or commercial products constitute endorsement or recommendation for use. This study was funded by the Bureau of Safety and Environmental Enforcement (BSEE), U.S. Department of the Interior, Washington, D.C. under Contract E14PC00011. Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Final Report Executive Summary Researchers use several approaches to generate information on scouring phenomena and gain understanding of seabed response to ice gouging. These approaches can be divided into two categories: observations of real events and artificial simulations. Observation of real events involves performing extensive site surveys (seabed scanning), identifying gouging characteristics, and locating areas with high gouging occurrence rates. Surveying has challenging technical and economical limitations, as discussed in the first task of this study. Artificial simulations can be useful tools to bridge the knowledge gaps and provide better understanding of the complexity of gouging processes. The advantage of simulations over field observations is that simulations allow full control of the test parameters (e.g., soil type, keel width and depth, attack angle, ice and subsea structure properties) that dictate the ice gouging response. Artificial simulations are classified into two types: • Physical testing • Numerical simulation Physical tests are conducted in the field or in laboratory settings using small– or large– scale instrumental setups. Physical testing can be performed under two different types of testing conditions: • The first type is ice gouge testing at normal gravity (1–g). This test can be performed indoors (laboratory) or outdoors (large–scale), depending on the size of the keel pushed into the soil bed to induce the gouge. Primary issues are associated with the range of confining stresses, uncertainty related to scaling laws, contact mechanics, interface conditions, and strain localization. • The second type of testing is performed in a centrifuge facility. The centrifuge applies an increased ‘gravitational’ acceleration to physical models to produce identical self–weight stresses in the model and prototype. Centrifuge testing has practical limitations related to the level of acceleration that can be applied and the size of the scale model used. Current computational capabilities make numerical simulation models cost effective. Simulations using finite element (FE) models have proven to be a fast–paced track for improving understanding of ice gouging. 100100.01.PL.REP.004 | Rev 0 | July 2015 Page 3 of 195 Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Final Report FE models used for simulating ice keel–soil–pipeline interactions mainly fall into two categories: • Structural FE models – The structural models assume that it is possible to decouple the interaction between ice and soil and the interaction between soil and pipe. In general, comparisons of pipe response predicted by the structural FE models and those measured in reduced scale physical tests have been reasonable but conservative. Feasibility studies or early phases of design can use structural FE models. • Continuum FE models – The continuum models resolve the coupled interactions between ice, soil, and pipe more accurately and therefore allow more realistic representations of the ice gouging process. These models, which usually predict lower subgouge soil displacements and lower pipeline strain demand compared to the structural models, have the potential to reduce burial depth requirements. The advantage of numerical simulations is their versatility and control over the parameters involved. However, the use of these simulations for design requires rigorous validation. Recommendations The following areas, which are discussed in detail in Section 8.0, should be addressed through combined multidisciplinary efforts: 1. Reduce uncertainty in input parameters. 2. Improve the numerical process through advancements in software package capabilities. 3. Reduce uncertainty in output parameters through validation. 100100.01.PL.REP.004 | Rev 0 | July 2015 Page 4 of 195 Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Final Report Revision History (Optional) Revision Date Comments A 05/15/2015 Issued for Internal Review B 06/19/2015 Issue for Client Review 0 07/14/2015 Issue for Client Approval HOLDS No. Section Comment Signatory Legend Revision Role Comments 0 Prepared Khaled Mostafa,Staff Consultant Markella K. Spari, Staff Specialist Checked Aiman Al–Showaiter, Staff Consultant Ronda Cavender, Senior Technical Editor Approved Jorge Alba, Senior Consultant 100100.01.PL.REP.004 | Rev 0 | July 2015 Page 5 of 195 Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Final Report Table of Contents 1.0 Introduction...................................................................................................................... 17 1.1 General ................................................................................................................................... 17 1.2 Report Objectives ................................................................................................................... 17 1.3 Abbreviations .......................................................................................................................... 17 2.0 The Arctic ......................................................................................................................... 19 2.1 Arctic Oil and Gas Reserves ................................................................................................... 19 2.2 Arctic Regions of Interest ........................................................................................................ 19 2.3 Key Arctic Challenges ............................................................................................................. 20 2.4 Ice Gouge Protection .............................................................................................................. 22 3.0 Ice Gouging ...................................................................................................................... 24 3.1 Definition ................................................................................................................................. 24 3.2 Considerations ........................................................................................................................ 25 3.2.1 Ice Keel ............................................................................................................................. 25 3.2.2 Icebergs ............................................................................................................................. 25 3.2.3 Sea Ice Ridges .................................................................................................................. 27 3.2.4 Seabed .............................................................................................................................. 27 3.2.5 Pipeline Design .................................................................................................................. 28 3.2.6 Wellhead Design ............................................................................................................... 29 3.3 Ice Gouge Processes ............................................................................................................. 33 3.3.1 Keel Motion ....................................................................................................................... 33 3.3.2 Soil Failure Mechanism ..................................................................................................... 34 3.3.3 Subgouge Deformations .................................................................................................... 39 3.4 Knowledge and Understanding of Ice Scouring...................................................................... 40 3.4.1 Real Events ....................................................................................................................... 40 3.4.2 Simulations ........................................................................................................................ 41 3.4.3 Comparison of Approaches for Ice Gouging Studies.......................................................... 43 4.0 Geotechnical Investigations ........................................................................................... 44 4.1 Beaufort Sea ........................................................................................................................... 44 4.1.1 Barnes and Reimnitz (1974) .............................................................................................. 45 4.1.2 Reimnitz et al. (1977) ......................................................................................................... 48 100100.01.PL.REP.004 | Rev 0 | July 2015 Page 6 of 195 Ice Scour and Gouging Effects with Respect to Pipeline and Wellhead Final Report 4.1.3 Miller and Bruggers (1980) ...............................................................................................
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