Macondo Well
Deepwater Horizon
Blowout
LESSONS FOR IMPROVING
OFFSHORE DRILLING SAFETY
Committee on the Analysis of Causes of the
Deepwater Horizon Explosion, Fire, and Oil Spill to
Identify Measures to Prevent Similar Accidents in the Future
Marine Board
Board on Environmental Studies and Toxicology

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Committee on the Analysis of Causes of the
Deepwater Horizon Explosion, Fire, and Oil Spill to
Identify Measures to Prevent Similar Accidents in the Future
Marine Board
Board on Environmental Studies and Toxicology
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COMMITTEE ON THE ANALYSIS OF CAUSES OF THE
DEEPWATER HORIZON EXPLOSION, FIRE, AND OIL SPILL TO
IDENTIFY MEASURES TO PREVENT SIMILAR ACCIDENTS IN THE FUTURE
Members
DONALD C. WINTER (Chair), University of Michigan, Ann Arbor
PAUL M. BOMMER, University of Texas at Austin
CHRYSSOSTOMOS CHRYSSOSTOMIDIS, Massachusetts Institute of
Technology, Cambridge
DAVID E. DANIEL, University of Texas at Dallas
THOMAS J. ECCLES, United States Navy, Washington, D.C.
EDMUND P. GIAMBASTIANI, JR., United States Navy (retired),
Warwick, Maryland
DAVID A. HOFMANN, University of North Carolina at Chapel Hill
ROGER L. MCCARTHY, McCarthy Engineering, Palo Alto, California
NAJMEDIN MESHKATI, University of Southern California, Los Angeles
KEITH K. MILLHEIM, Strategic Worldwide, LLC, The Woodlands,
Texas (Resigned November 28, 2011, prior to completion of the
committee’s report)
M. ELISABETH PATÉ-CORNELL, Stanford University, Stanford, California
ROBERT F. SAWYER, University of California at Berkeley
JOCELYN E. SCOTT, DuPont Engineering, Facilities and Real Estate,
Wilmington, Delaware
ARNOLD F. STANCELL, Georgia Institute of Technology,
Greenwich, Connecticut
MARK D. ZOBACK, Stanford University, Stanford, California
Staff
RAYMOND A. WASSEL, Project Director
v
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MARINE BOARD
MICHAEL S. BRUNO (Chair), Stevens Institute of Technology, Hoboken,
New Jersey
THOMAS M. LESCHINE (Vice Chair), University of Washington, Seattle
STEVEN R. BARNUM, Hydrographic Consultation Services, Suffolk, Virginia
JERRY A. BRIDGES, Virginia Port Authority, Norfolk
MARY R. BROOKS, Dalhousie University, Halifax, Nova Scotia, Canada
JAMES C. CARD, Maritime Consultant, The Woodlands, Texas
STEPHEN M. CARMEL, Maersk Line Limited, Norfolk, Virginia
EDWARD N. COMSTOCK, Raytheon Company, Sudbury, Massachusetts
STEPHAN TONI GRILLI, University of Rhode Island, Narragansett
DOUGLAS J. GRUBBS, Crescent River Port Pilots Association,
Metairie, Louisiana
FREDERICK J. HARRIS, General Dynamics, San Diego, California
JUDITH HILL HARRIS, City of Portland, Maine
JOHN R. HEADLAND, Moffatt & Nichol Engineers, New York, New York
JOHN M. HOLMES, Port of Los Angeles, San Pedro, California
DONALD LIU, Marine Consultant, Willis, Texas
RICHARD S. MERCIER, Texas A&M University, College Station
EDMOND J. MORAN, JR., Moran Towing Corporation, New
Canaan, Connecticut
ALI MOSLEH, University of Maryland, College Park
GEORGE BERRYMAN NEWTON, QinetiQ North America, Marstons
Mills, Massachusetts
PETER K. VELEZ, Shell International Exploration and Production, Inc.,
Houston, Texas
JOHN WILLIAM WAGGONER, HMS Global Maritime, New Albany, Indiana
TRANSPORTATION RESEARCH BOARD
2011 EXECUTIVE COMMITTEE OFFICERS
NEIL J. PEDERSEN (Chair), Administrator, Maryland State Highway
Administration (retired), Baltimore
SANDRA ROSENBLOOM (Vice Chair), Professor of Planning, University of
Arizona, Tucson
C. MICHAEL WALTON (Division Chair for NRC Oversight), Ernest H. Cockrell
Centennial Chair in Engineering, University of Texas, Austin
ROBERT E. SKINNER, JR. (Executive Director), Transportation Research Board
vi
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BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
Members
ROGENE F. HENDERSON (Chair), Lovelace Respiratory Research
Institute, Albuquerque, New Mexico
PRAVEEN AMAR, Clean Air Task Force, Boston, Massachusetts
TINA BAHADORI, American Chemistry Council, Washington, D.C.
MICHAEL J. BRADLEY, M.J. Bradley & Associates, Concord, Massachusetts
JONATHAN Z. CANNON, University of Virginia, Charlottesville
GAIL CHARNLEY, HealthRisk Strategies, Washington, D.C.
FRANK W. DAVIS, University of California, Santa Barbara
RICHARD A. DENISON, Environmental Defense Fund, Washington, D.C.
CHARLES T. DRISCOLL, JR., Syracuse University, New York
H. CHRISTOPHER FREY, North Carolina State University, Raleigh
RICHARD M. GOLD, Holland & Knight, LLP, Washington, D.C.
LYNN R. GOLDMAN, George Washington University, Washington, D.C.
LINDA E. GREER, Natural Resources Defense Council, Washington, D.C.
WILLIAM E. HALPERIN, University of Medicine and Dentistry of New
Jersey, Newark
PHILIP K. HOPKE, Clarkson University, Potsdam, New York
HOWARD HU, University of Michigan, Ann Arbor
SAMUEL KACEW, University of Ottawa, Ontario, Canada
ROGER E. KASPERSON, Clark University, Worcester, Massachusetts
THOMAS E. MCKONE, University of California, Berkeley
TERRY L. MEDLEY, E.I. du Pont de Nemours & Company,
Wilmington, Delaware
JANA MILFORD, University of Colorado at Boulder
FRANK O’DONNELL, Clean Air Watch, Washington, D.C.
RICHARD L. POIROT, Vermont Department of Environmental
Conservation, Waterbury
KATHRYN G. SESSIONS, Health and Environmental Funders Network,
Bethesda, Maryland
JOYCE S. TSUJI, Exponent Environmental Group, Bellevue, Washington
Senior Staff
JAMES J. REISA, Director
DAVID J. POLICANSKY, Scholar
RAYMOND A. WASSEL, Senior Program Officer for Environmental Studies
ELLEN K. MANTUS, Senior Program Officer for Risk Analysis
SUSAN N.J. MARTEL, Senior Program Officer for Toxicology
EILEEN N. ABT, Senior Program Officer
RUTH E. CROSSGROVE, Senior Editor
MIRSADA KARALIC-LONCAREVIC, Manager, Technical Information Center
RADIAH ROSE, Manager, Editorial Projects
vii
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DEDICATION
We dedicate this report to the memory of the eleven people who lost their
lives on board the Deepwater Horizon on April 20, 2010.
Jason Christopher Anderson
Aaron Dale Burkeen
Donald Neal Clark
Stephen Ray Curtis
Gordon Lewis Jones
Roy Wyatt Kemp
Karl Dale Kleppinger, Jr.
Keith Blair Manuel
Dewey Allen Revette
Shane Michael Roshto
Adam Taylor Weise
viii
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Preface
The blowout of the Macondo well on April 20, 2010, led to enormous
consequences for the individuals involved in the drilling operations and for their
families. Eleven workers on the Deepwater Horizon drilling rig lost their lives,
and 16 others were seriously injured. There were also enormous consequences
for the companies involved in the drilling operations, to the Gulf of Mexico en-
vironment, and to the economy of the region and beyond. The flow continued
for nearly 3 months before the well could be completely killed, during which
time nearly 5 million barrels of oil spilled into the gulf. The economic conse-
quences of the event were felt almost immediately and became more widespread
over time. A moratorium on drilling activities was put in place throughout the
gulf, and commercial fishing was halted in much of the region. The total eco-
nomic impact is in the tens of billions of dollars. The long-term ecological im-
pact will likely take many years to measure. This was truly a “spill of national
significance,”1 and international efforts to learn from this disaster have been
spurred.
Shortly after the event, the National Academy of Engineering (NAE) and
the National Research Council (NRC) were asked by the Secretary of the Inte-
rior to form a committee to examine the probable causes of the Deepwater Hori-
zon explosion, fire, and oil spill and to identify means for preventing similar
harm in the future. The committee benefited from a focused and well-defined
scope, which excluded several issues such as the extensive response and reme-
diation efforts (see Appendix A). Nonetheless, NAE and NRC wanted to ensure
that the committee had not only the requisite expertise appropriate to a deepwa-
ter drilling accident but also the breadth needed to ensure that the root causes of
the incident and appropriate corrective actions could be identified. Conse-
quently, a committee of 15 members was assembled, which provided expertise
in geophysics, petroleum engineering, marine systems, accident investigations,
safety systems, risk analysis, human factors, and organizational behavior (see
the biographical information at the end of this document).
1
Designation made by the Secretary of Homeland Security on April 29, 2010.
ix
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x Preface
The committee was able to take advantage of other investigations occur-
ring at the same time, such as the Marine Board of Investigation (MBI), con-
vened by the U.S. Coast Guard (USCG) and the Bureau of Ocean Energy Man-
agement, Regulation, and Enforcement (BOEMRE—formerly the Minerals
Management Service). Members of the committee observed the MBI hearings
and reviewed documentation submitted to the board. Similarly, committee
members observed hearings of the National Commission on the BP Deepwater
Horizon Oil Spill and Offshore Drilling and the U.S. Chemical Safety Board.
The committee conducted its own public meetings to hear presentations from
regulators (USCG, BOEMRE, and the Republic of the Marshall Islands—the
flag state), the American Petroleum Institute, the American Bureau of Shipping,
and industry (see Appendix B).
The information provided to the committee by industry was constrained
by the legal environment generated by the MBI, the investigation of the De-
partment of Justice, and the prospect of multiple matters of civil litigation in-
volving tens of billions of dollars. However, some of the companies involved in
the Deepwater Horizon incident participated in the committee’s public meetings
and submitted material in writing, including several corporate investigative re-
ports. BP, Halliburton, and Transocean provided information to the committee.
Cameron, manufacturer of the Deepwater Horizon’s blowout preventer (BOP),
provided some material but declined to make a presentation on the Deepwater
Horizon BOP.
The committee also benefited from good support by USCG, which facili-
tated access to recovered items from Deepwater Horizon (lifeboats, riser, drill
pipe, and BOP). The BOP assessment was greatly aided by the forensic work
performed by Det Norske Veritas (DNV) and reported by DNV (2011a, 2011b).
However, the committee was unable to obtain results of Phase 2 testing of the
Deepwater Horizon BOP led by BP. The results are maintained under protective
orders by the courts supervising related litigation matters.
The committee received support from a number of industrial organizations
that were not directly involved in the Macondo well–Deepwater Horizon inci-
dent, which improved its understanding of the various standards and practices of
the industry. Of note, Shell provided access both to its Real-Time Operations
Center in Houston, Texas, and to the Deepwater Nautilus, the sister ship to
Deepwater Horizon. Hydril similarly provided access to its BOP design, produc-
tion, and test facilities. The committee also visited Wild Well Control School in
Houston to improve its understanding of the training provided to drilling per-
sonnel. In addition to the industry inputs provided through corporate channels,
the committee was able to obtain inputs from industry personnel reflected in
written summaries provided by the Society of Petroleum Engineers and the In-
ternational Association of Drilling Contractors. The summaries were prepared
with the prior understanding that none of the input would be attributed to spe-
cific individuals. To obtain a better understanding of alternative regulatory ap-
proaches, committee members visited the Petroleum Safety Authority of Nor-
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xi
Preface
way, SINTEF (Stiftelsen for Industriell og Teknisk Forskning), the Norwegian
Oil Industry Association, and the U.K. Health and Safety Executive.
The scope and depth of the information available to the committee enabled
it to develop findings and informed observations concerning the probable causes
(both direct and root causes) of the incident. The information also enabled the
committee to develop a series of recommendations that it believes will reduce
the likelihood and impact of any future well control incidents. This final report
documents the major findings, observations, and recommendations developed by
the committee during its study.2 The report does not attempt to assign responsi-
bility for the incident to specific individuals or corporations, nor does it attempt
to make a systematic assessment of the extent to which the parties involved
complied with applicable regulations. Such matters were deemed to be appropri-
ately addressed by the MBI.
The committee notes that several of its recommendations reinforce steps
already taken to strengthen regulatory practices in the aftermath of this incident.
These are steps in the right direction, which need to be built on in a timely man-
ner to ensure that the risks associated with this critical industry are minimized
and that the public trust in both industry operations and regulatory processes is
restored. Many challenges beyond those addressed in this report must be faced
to revitalize the regulatory process. In particular, the administration and Con-
gress will need to provide the funding and flexibility in hiring practices that will
allow the Bureau of Safety and Environmental Enforcement (BSEE)3 to enhance
its capability and capacity.
There have been positive indications regarding industry’s recognition of
the need for change, as well. Notable have been the formation and funding of
additional response capabilities, such as the Marine Well Containment Com-
pany. That said, the companies involved in the Macondo well–Deepwater Hori-
zon incident have the added challenge of ensuring that positions taken to defend
against civil liabilities and potential criminal charges do not inhibit their timely
recognition of the need to change their internal processes and the manner in
which the many parties to this industry (operating companies, drilling contrac-
tors, and service companies) all work together.
The need to maintain domestic sources of oil is great, but so is the need to
protect the lives of those who work in this industry and to protect the Gulf of
Mexico and the many other industries that depend on it. The oil and gas industry
2
The committee issued an interim letter report on November 16, 2010, which pre-
sented preliminary findings and observations concerning key factors and decisions that
may have contributed to the blowout of the Macondo well. The committee also provided
a letter to BOEMRE on September 17, 2010, which identified potential approaches for
use in conducting forensic analyses of the Deepwater Horizon BOP.
3
On October 1, 2011, BOEMRE split into two entities. BSEE is currently the federal
entity responsible for safety and environmental oversight of offshore oil and gas opera-
tions internal processes and the manner in which the many parties to this industry (operat-
ing companies, drilling contractors, and service companies) work together.
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xii Preface
is robust and capable of improving offshore drilling safety; it employs many
experienced personnel and utilizes many impressive technologies. Similarly,
there are many dedicated and capable individuals in the various regulatory agen-
cies responsible for overseeing the industry who can make further safety im-
provements. There is no reason why the diligent application of these multifold
capabilities toward strengthening system safety should not significantly reduce
the likelihood and consequences of any future loss of well control in the Gulf of
Mexico.
Donald C. Winter, Chair
Committee on the Analysis of Causes of the Deepwater
Horizon Explosion, Fire, and Oil Spill to Identify
Measures to Prevent Similar Accidents in the Future
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Acknowledgments
This report has been reviewed in draft form by individuals chosen for their
diverse perspectives and technical expertise in accordance with procedures ap-
proved by NRC’s Report Review Committee. The purpose of this independent
review is to provide candid and critical comments that assist the authors and
NRC in making the published report as sound as possible and to ensure that the
report meets institutional standards for objectivity, evidence, and responsiveness
to the study charge. The review comments and draft manuscript remain confi-
dential to protect the integrity of the deliberative process. We thank the follow-
ing individuals for their review of this report: Benton F. Baugh, Radoil Inc.,
Houston, Texas; Robert Bea, University of California, Berkeley (emeritus); Mi-
chael J. Burke, Tulane University, New Orleans, Louisiana; Vice Admiral James
C. Card (USCG, retired), The Woodlands, Texas; Elmer Danenberger III, inde-
pendent consultant, Reston, Virginia; Chan Gill, independent consultant, Avon-
dale, Arizona; Richard Hartley, B&W Pantex, Amarillo, Texas; Trevor O. Jones,
ElectroSonics Medical Inc., Cleveland, Ohio; Rear Admiral Malcolm
MacKinnon III (U.S. Navy, retired), MSCL LLC, Alexandria, Virginia; Erik B.
Nelson, independent consultant, Houston, Texas; Robin Pitblado, Det Norske
Veritas (U.S.A.), Inc., Katy, Texas; Christopher Ranger, Ranger Consultants,
Ltd., Ayrshire, Scotland; Frank J. Schuh, Drilling Technology, Inc., Plano,
Texas; Richard Sears, Leading Energy Now, Houston, Texas; and A. Dan Tar-
lock, Chicago Kent College of Law, Chicago, Illinois.
Although the reviewers listed above provided many constructive com-
ments and suggestions, they were not asked to endorse the committee’s conclu-
sions or recommendations, nor did they see the final draft of the report before its
release. The review of this report was overseen by Robert A. Frosch, Harvard
University, Cambridge, Massachusetts, and by C. Michael Walton, University of
Texas, Austin. Appointed by NRC, they were responsible for making certain
that an independent examination of this report was carried out in accordance
with institutional procedures and that all review comments were carefully con-
sidered. Responsibility for the final content of this report rests entirely with the
authoring committee and the institution.
xiii
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xiv Acknowledgments
The work of the committee was assisted by three consultants. Michael
Griffes, Alexandria, Virginia, and Peter Johnson, Washington, D.C., facilitated
information-gathering activities. Stephen Kemp, Marine & Process Controls
LLC, Whitmore Lake, Michigan, provided analysis of the Deepwater Horizon
control and alarm systems.
This project was overseen by the Marine Board, a component of the NRC’s
Transportation Research Board (TRB), with support from the Board on Environ-
mental Studies and Toxicology of the NRC’s Division on Earth and Life Studies.
Raymond Wassel managed the study under the guidance of the committee
and the supervision of Stephen Godwin, Director, Studies and Special Programs,
TRB. Beverly Huey and Mirsada Karalic-Loncarevic provided scientific and tech-
nical information. Norman Solomon edited the report; Jennifer Weeks prepared
the prepublication manuscript, under the supervision of Javy Awan, Director of
Publications, TRB. Radiah Rose assisted in preparing the prepublication manu-
script and the final published version. Mark Hutchins and Orin Luke arranged
meetings and provided logistical communications to the committee. In addition,
Keri Schaffer helped with gathering and compiling background information.
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Abbreviations
ABS American Bureau of Shipping
ALARP as low as reasonably practicable
AMF automatic mode function
AoC acknowledgment of compliance
API American Petroleum Institute
ASRS Aviation Safety Reporting System
BOEMRE Bureau of Ocean Energy Management,
Regulation, and Enforcement
BOP blowout preventer
BSR blind shear ram
BSEE Bureau of Safety and
Environmental Enforcement
CAIB Columbia Accident Investigation Board
CCPS Center for Chemical Process Safety
CDC Centers for Disease Control and Prevention
CGD combustible gas detector
CSB U.S. Chemical Safety Board
CSR casing shear ram
DHSG Deepwater Horizon Study Group
DNV Det Norske Veritas
DoD U.S. Department of Defense
DOI U.S. Department of the Interior
ECD equivalent circulating density
EDS emergency disconnect system
EIA U.S. Energy Information Administration
EMW equivalent mud window
EPA U.S. Environmental Protection Agency
EPRI Electric Power Research Institute
E&P exploration and production
ESD emergency shutdown
FAA Federal Aviation Administration
FBI Federal Bureau of Investigation
FS flag state
GAO U.S. General Accounting Office
xv
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xvi Abbreviations
HSE Health and Safety Executive of the
United Kingdom
IACS integrated alarm and control system
IADC International Association of Drilling Contractors
IAEA International Atomic Energy Agency
IBOP internal blowout preventer
LCM lost circulation material
LMRP lower marine riser package
MBI Marine Board of Investigation
MGS mud–gas separator
MMS Minerals Management Service
MODU mobile offshore drilling unit
MUX multiplexer
MWCC Marine Well Containment Company
NAE National Academy of Engineering
NEI Nuclear Energy Institute
NOAA National Oceanic and Atmospheric
Administration
NPC National Petroleum Council
NRC National Research Council
NTSB National Transportation Safety Board
OECD Organisation for Economic Cooperation
and Development
OIM offshore installation manager
OLF Norwegian Oil Industry Association
ppg pounds per gallon
Presidential Commission National Commission on the BP Deepwater
Horizon Oil Spill and Offshore Drilling
PSA Petroleum Safety Authority of Norway
ROV remotely operated vehicle
SEMS Safety and Environmental Management Systems
SINTEF Stiftelsen for Industriell og Teknisk Forskning
SPE Society of Petroleum Engineers
SUBSAFE U.S. Navy’s Submarine Safety Program
TSA Transportation Security Administration
USCG U. S. Coast Guard
U.S. NRC U.S. Nuclear Regulatory Commission
VBR variable bore ram
WCID well construction interface document
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Contents
Summary............................................................................................................. 3
1 Introduction .............................................................................................. 10
Challenges in Designing and Constructing Offshore Wells, 11
Several Past Accidents Caused by Blowouts, 14
History of Macondo Well Before the Blowout, 14
Committee’s Approach to Its Task, 15
Other Investigations, 17
2 Well Design and Construction ................................................................. 19
Overview of the Macondo Well Plan, 19
Findings, 25
Observations, 39
Recommendations, 43
3 Blowout Preventer System ....................................................................... 45
BOP System for Deepwater Horizon, 45
Areas of Investigation, 52
Findings, 68
Observations, 73
Recommendations, 73
4 Mobile Offshore Drilling Units ................................................................ 75
Deepwater Horizon Rig, 75
Findings, 82
Observations, 85
Recommendations, 85
5 Industry Management of Offshore Drilling ............................................ 90
Safety Culture, 92
Recommendations, 104
xvii
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xviii Contents
6 Regulatory Reform ................................................................................. 111
Regulation of U.S. Offshore Drilling Before the Macondo
Well Blowout, 112
DOI’s Safety and Environmental Management Systems, 114
Goal-Oriented Risk Management Regulatory Systems, 116
Recommendations, 120
7 Concluding Comments ........................................................................... 128
References ....................................................................................................... 130
APPENDICES
A Statement of Task ..................................................................................... 136
B Public Agendas of the Committee on the Analysis of Causes of
the Deepwater Horizon Explosion, Fire, and Oil Spill to Identify
Measures to Prevent Similar Accidents in the Future ............................... 138
C Findings, Observations, and Recommendations ....................................... 142
D Calculating the Differential Pressure at the Start of the
Negative Test and the Quality of Foam Cement ....................................... 166
Study Committee Biographical Information ............................................... 170
BOXES, FIGURES, AND TABLES
BOX
1-1 Reports of Other Macondo Well–Deepwater Horizon
Investigations, 18
FIGURES
2-1 Original wellbore architecture planned for Macondo well, 21
2-2 Final wellbore architecture for Macondo well, 22
2-3 Overburden stress, fracture gradients in the shale and sands, and
pore pressure in the Macondo well, 23
2-4 Variation of pore pressure in the open hole section of the Macondo
well expressed in pounds per gallon, 24
2-5 Planned cement location and likely cement location after pumping, 29
2-6 Calculated foam density versus depth during pumping, 30
2-7 Uncontaminated cement compressive strength tests
(DP = differential pressure), 31
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xix
Contents
2-8 Float collar with flapper valves and differential fill tube, 34
2-9 View inside casing hanger, 36
3-1 Deepwater Horizon BOP port side, 47
3-2 Sketch of intended nominal operation of BSR in the Macondo well, 48
3-3 Upper and lower shear blades crushing the drill pipe and beginning
the shearing (or breaking) operation, 48
3-4 Macondo well blowout timeline, 60
3-5 Finite element analysis model of BSR blade surfaces and
off-center drill pipe, 63
3-6 Progression of off-center BSR shear model, isometric view (top)
and top view showing deformation of drill pipe outside of
shearing blade surfaces (bottom), 65
4-1 Basic dimensions of the Deepwater Horizon rig while drilling, 76
4-2 Illustration of the main deck of the Deepwater Horizon, 80
5-1 Selected major petroleum mergers (1996–2002), 97
D-1 Well diagram, 166
TABLES
2-1 Chevron Data to Illustrate the Effect of Mud Contamination on
Cement Compressive Strength, 33
6-1 Offshore Drilling Operations and Relevant Federal Agencies, 124
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