FACULTY OF SCIENCE AND TECHNOLOGY MASTER’S THESIS Study programme/specialisation: Spring semester, 2018 Petroleum Engineering (Drilling Technology) Open / Confidential Author: Mari Røstvig Tveit Digital submission (signature of author) Programme coordinator: Mahmoud Khalifeh Supervisor(s): Mahmoud Khalifeh (UiS), Tor Nordam (SINTEF Ocean) Title of master’s thesis: Understanding Leakage Rates in Permanently Abandoned Wells by Studying Natural Hydrocarbon Seepages Credits: 30 ECTS Keywords: Number of pages: 144 Permanent plug and abandonment Natural hydrocarbon seepages + supplemental material/other: 0 Oil / gas seeps Fate analysis Leaking wells Stavanger, 15th June 2018 Spring 18 Understanding Leakage Rates in Permanently Abandoned Wells by Studying Natural Hydrocarbon Seepages By Mari Røstvig Tveit This work is submitted in partial fulfillment of the requirements for the degree of Master of Science (MSc) within Petroleum Engineering at the University of Stavanger To Leon, For knowing before myself that I would love engineering i ABSTRACT Permanent plug and abandonment (PP&A) of wells is steadily becoming more important on the Norwegian Continental Shelf (NCS), as a large number of fields are approaching end of their productive life. Combining operational, material, and qualification challenges, it is evident that risk of leaks exists from permanently abandoned wells. To ensure the protection of our environment, well integrity standard NORSOK D-010 constitutes zero leak acceptance criteria; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. To evaluate the fate of leaking oil and/or gas from abandoned wells, two real cases from the NCS, one historical gas leak (Field A) and one theoretical oil leak (Field B), have been subject to fate analysis, executed using software from SINTEF Ocean’s Marine Environmental Modeling Workbench (MEMW). For Field A, it is found that approximately 95 to 99% of the leaking gas dissolves while rising through the water column. The fraction of gas transported to atmosphere is a function of the initial gas bubble size and ambient temperature. The fate of oil is more complex than gas, but results show that due to its persistent nature, released oil will be able to travel more than hundred kilometers away from the release point. Due to this dispersion, concentrations, the main factor controlling toxicity, will be greatly diluted. Fate of oil is dependent on chemical composition; lighter compounds will evaporate to the atmosphere, while heavy compounds will be deposited on the seafloor. Evaporation, sedimentation and biodegradation are the main contributing mechanisms in fate analysis of oil. ii ACKNOWLEDGEMENTS I would like to express my gratitude to the number of people that made this work possible: • First and foremost, I would like to sincerely thank my supervisor at the University of Stavanger, Mahmoud Khalifeh; for believing in me, for always being available and for always making me feel welcome in your office. I really enjoyed my time! • To Tor Nordam, my co-supervisor at SINTEF Ocean; thank you for teaching me the software, for providing me with scripts and for your kindness and willingness to help. • To SINTEF Ocean; for providing me with access to your excellent software, thank you, I am very grateful. • To Ivar Blaauw, Lars Hovda and the rest of the team at ConocoPhillips; thank you for all of your time and input, from start to finish. This work has benefited a lot from our conversations. • To all PAF members; for inviting me to present my work at your meeting, thank you for your time and interesting discussion. • To Øystein Arild and Hans Petter Lohne; for providing me with useful input when pitching the idea of the project, thank you. • To Martin Hovland; thank you for sharing your knowledge with me and helping me put things in a larger perspective. Lastly, I would like to thank my family for all of their love and support throughout the years. The biggest thank you of all goes to Andreas; for your continuous support, encouragement, humour and tough love, I would never have been able to complete this work without you. I love you! Mari Tveit Stavanger 2018 iii TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... ii ACKNOWLEDGEMENTS ............................................................................................................ iii LIST OF FIGURES ...................................................................................................................... viii LIST OF TABLES ........................................................................................................................... xi NOMENCLATURE ...................................................................................................................... xii 1. INTRODUCTION ........................................................................................................................ 1 1.1 Permanent Plug & Abandonment ........................................................................................... 1 1.1.1 Plug and abandonment activities in the North Sea ......................................................... 1 1.1.2 Regulatory authorities ..................................................................................................... 2 1.1.3 Regulatory authorities in the North Sea .......................................................................... 2 1.2 Well barrier ............................................................................................................................. 3 1.2.1 Well barrier materials ...................................................................................................... 5 1.2.2 Barrier failure modes ...................................................................................................... 6 1.2.2.1 Leakage through the bulk material ............................................................................... 7 1.2.2.2 Leakage around the bulk material ................................................................................ 7 1.2.2.3 Shift in barrier position ................................................................................................ 8 1.2.3 Well barrier verification .................................................................................................. 9 1.3 Challenges in permanent plug and abandonment ................................................................. 12 1.3.1 Leaks through permanently abandoned wells ............................................................... 13 1.4 Objectives of the thesis ......................................................................................................... 15 1.5 Methodology ........................................................................................................................ 16 2. NATURAL HYDROCARBON SEEPAGES ............................................................................. 17 2.1 Terminology ......................................................................................................................... 19 2.1.1 Seep and seepage .......................................................................................................... 19 iv 2.1.2 Macro-seeps vs. microseepage ...................................................................................... 20 2.1.3 Origin of hydrocarbon seepages ................................................................................... 20 2.1.4 Classifying seeping gas ................................................................................................. 21 2.1.5 Degradation of natural gas ............................................................................................ 23 2.1.6 How seeps affect the seabed ......................................................................................... 25 2.2 Natural hydrocarbon seepage in Norway and in the North Sea ........................................... 26 2.2.1 Tommeliten seep area ................................................................................................... 27 2.3 Oil and gas seeps in North America ..................................................................................... 29 2.3.1 Seeps offshore California .............................................................................................. 29 2.3.2 The Gulf of Mexico ....................................................................................................... 30 3. METHODOLOGY ..................................................................................................................... 32 3.1 Fate modeling ....................................................................................................................... 32 3.2 Case studies .......................................................................................................................... 36 3.2.1 Field A ........................................................................................................................... 37 3.2.2 Field B ........................................................................................................................... 40 3.3 Software ................................................................................................................................ 41 3.3.1 The OSCAR model ......................................................................................................