Contribution to Well Integrity and Increased Focus on Well Barrieres From Life Cycle Aspect

7/30/2019 Contribution to Well Integrity and Increased Focus on Well Barrieres From Life Cycle Aspect

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Contribution to well integrity andincreased focus on well barriers from a

life cycle aspect

by

Birgit Vignes

Thesis submitted in fulfillment ofthe requirements for the degree of

PHILOSOPHIAE DOCTOR(PhD)

Faculty of Science and TechnologyUniversity of Stavanger

2011


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University of StavangerN-4036 StavangerNORWAY

2011 Birgit Vignes

ISBN: 978-82-7644-478-0ISSN: 1890-1387


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Preface

This thesis is submitted in fulfillment of the requirements for the degree ofPhilosophiae Doctor (PhD) at the University of Stavanger, Norway, Facultyof Science and Technology. Most of the research presented has been carriedout at the Petroleum Safety Authority Norway and some work is performed atthe University of Stavanger in the period from August 2007 to August 2011.The compulsory courses attended have been given at the University ofStavanger.

The thesis consists of two parts. In Part I, a summary and an introduction to

the work are given, and Part II consists of eight papers about well integritywithin the offshore oil and gas industry. The work has been funded by thePetroleum Safety Authority, Norway, and I wish to acknowledge thePetroleum Safety Authority for financing my research, for their support andflexible arrangements. I would like to show my gratitude to my supervisorProfessor Bernt S. Aadny for excellent supervision and support during myPhD work. Also a special thanks to Kristen Kjeldstad, Stein A. Tonning,Jayantha P. Liyanage, Arne M. Enoksen, Jan Andreassen, Monika Ovesen andHilde Heber. Thank you all for your willingness to share your time,experience and knowledge and for your comments on this thesis. I would alsolike to thank all my colleagues at the Petroleum Safety Authority,Department of Drilling and Well Technology: Hilde Karin stnes, SveinArve Askedal, Johnny Gundersen, Eirik Vaktdal, Kjell Marius Auflem, OlaHeia, Norunn Braa, Mette Elise Vintermyr and Reidar Hamre for invaluableencouragement in general. All of them have always been available fordiscussions and have given quick and constructive feedback throughout thecourse of this work. I wish to acknowledge Kari Tury, Nina Egeland Skjeie,Elisabeth Sekkester and Svein Jonasen for supporting me during this work.

I would also like to thank friends for support and motivation during this work.And finally, to the greatest supporters of all, my family! I would like to thankmy husband Frode and my children Synne, Sondre and Oline for all their loveand support. I am really looking forward to spending more time with you all!

Stavanger, August 2011

Birgit Vignes


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Scientific Environments

Co-authors

Birgit Vignes, University of Stavanger. Faculty of Science andTechnology, Norway. Department of Petroleum Technology andPetroleum Safety Authority, Norway.

Bernt Sigve Aadny, University of Stavanger. Faculty of Scienceand Technology, Norway. Department of Petroleum Technology.

Jayantha Prasanna Liyanage, University of Stavanger. Faculty ofScience and Technology, Norway. Department of Mechanical andStructural Engineering and Material Science.

Stein Arild Tonning, Petroleum Safety Authority, Norway.Department of Drilling and Well Technology.

Arne Mikal Enoksen, Petroleum Safety Authority, Norway.Department of Drilling and Well Technology.

Monica Ovesen, Petroleum Safety Authority, Norway.

Department of Drilling and Well Technology.


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Summary

This project started when my colleague Jan Andreassen sent me anarticle about a well integrity survey performed by Kevin Burton in theUnder Water Group (UWG) in which one in ten UK wells have beenshut in on structural integrity issues10. Jan and I travelled to the UWGin Norwich where they gave us many ideas for how to perform the wellintegrity surveys on the Norwegian Continental Shelf (NCS) and later

in the Netherlands. I have been working for the Petroleum SafetyAuthority (PSA) during this work, and, together with my colleagues, Ihave performed several projects and audits related to well integrity onthe Norwegian Continental shelf (NCS) which are included in mythesis.

The thesis is an attempt to contribute to identifying some of the wellintegrity challenges on the Norwegian Continental Shelf (NCS) and inthe Netherlands. The thesis presents the possible reasons why leakageoccur in well barrier elements such as tubing, casing, cement, blow out

preventer (BOP) and annulus safety valve (ASV). It identifies some of

the well integrity challenges in injection wells (including CO2injection), production wells (including wells on gas lift), multilateralwells and temporary abandoned wells. The thesis describes some of thetechnical challenges related to qualification of well barrier elementsand presents some possible reasons for well integrity problems relatedto human factors and the operators working situation offshore.

The thesis consists of two parts. Part I provides an introduction to wellintegrity, barriers including well barriers and well barrier elements,human factors and human, technology and organization (HTO) aspectsas contributing factors to well integrity. Part II consists of eight papers

presenting the well integrity surveys performed on the NCS and in theNetherlands, the well integrity challenges in CO2 injection wells andadjacent wells, qualification of well barrier elements and the human,technology and organization (HTO) aspects as contributing factors toimproving the drillers and wireline operators working situationoffshore and thereby indirectly improving well integrity.


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Article I provides an introduction to the well integrity status on theNorwegian Continental Shelf (NCS) in 20064. The well integrity surveywas based on well integrity information from seven operatingcompanies, 12 offshore facilities and 406 wells. The survey indicatedthat 18% of the selected wells had well integrity issues and 7% of thesewere shut in. The survey showed that the industry had well integritychallenges related to well barrier elements such as tubing, annulussafety valve (ASV), casing, cement, wellhead and packers. The surveyidentified areas for improvement related to well documentation,handover documentation, regular condition monitoring, application of

NORSOK D-010, consistent practice within the company, managementof change, competence and training, openness and exchange ofexperience, reliability analyses and performance indicators. The resultsfrom the survey indicated a relatively low number of reported wellintegrity failures in subsea wells, and indicated that this can beexplained by the limited possibility to monitor these wells. The paperalso presents the results from five technical audits conducted in the

period 2003200617,18,19,20,21. The audits were performed in order tounderstand the technical aspects in the selected wells with wellintegrity failures. The technical and operational investigations includedevaluation of the design manuals, methodology for data collection and

well design. The audits included well incidents with significant impactand potential for serious accidents (several companies and various wellcategories). These occurred because of long-term effects not beingsufficiently considered during the design phase, unclear understandingof barriers, weaknesses in well design and planning processes, andoperational decisions during abnormal situations. The audits concludedthat the normal industry approach was to focus on frequent and low-consequence incidents.

Article II presents a well integrity study for the injection wells on theNCS in 20087. This study represented six operators and included water

injectors, gas injectors and water alternating gas (WAG) wells. Thestudy showed that the integrity problems in the injection wells wererelated to the completion design (Polish bore receptacle (PBR) and sealstem), the oxygen level in the injected water and the design of theWAG wells.


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Article III includes some of the well integrity challenges in theNetherlands11. The Petroleum Safety Authority Norway (PSA) assistedthe Supervision of Mines Netherlands (SSM) during a well integrityinspection supervisory activity in the Netherlands in 2008. This activitywas based on input from ten operating companies and 31 wells. Theoutcome of the evaluation regarding the well integrity performance inthe Netherlands is based on the industry standard NORSOK D-010.

NORSOK D-010 is not an international standard and is not referencedin regulations and guidelines used in the Netherlands. The findings andconclusions referenced in NORSOK D-010 do not directly correspond

to established criteria of drilling and well requirements according to theregulations in the Netherlands. The survey showed that 13% of 31selected wells had well integrity problems, and 3% of the wells wereshut in due to integrity problems. The supervisory activity identifiedareas for improvement for all the operators related to personnelcompetency, document control, management system, well designcriteria, condition monitoring, well handover and experience transfer.

Article IV identifies some of the technical challenges related to CO2injection and the adjacent wells32. Adjacent wells are defined in the

paper as wells that can be exposed to the injected CO2. In order to

implement CO2 injection and storage on a widespread scale, some workneeds to be performed related to well integrity at the organizational andthe technical levels to further adapt appropriate frameworks,regulations and standards, and it is important to include the adjacentwells in these considerations. The industry needs a common industry

practice related to the design of wells adjacent to CO2 injection wellsand the plugging & abandonment of CO2 injection wells. A CO2injected reservoir may be penetrated by a number of adjacent wells thatcan be potential leakage sources. The paper presents challenges relatedto seismic surveys, the injected carbon dioxide medium includingcorrosion, long-term integrity and temperatures.

Article V presents some of the International Organization forStandardization (ISO) and American Petroleum Institute (API)international standards that the petroleum industry uses to qualify well

barrier elements such as BOP, packers and bridge plugs, subsurfacesafety valves, casing and tubing connections, gas lift equipment, and


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cement. The paper presents some of the industry challenges related toqualification and testing of well barrier elements including the exposedmedium, temperature and long-term integrity.

Article VI identifies the critical performance influencing factors (PIFs)according to Redmill (1997)30 within drilling and wireline operations

based on the experience from PSA projects and audits82, 83 and 84. ThePIFs affect human performance, human abilities to perform actions in asafe and efficient manner and human ability to improvise and improvework performance. The understanding of the interaction between HTOand the knowledge about PIFs is critical to achieving the goals of safeand effective drilling and well operations. PIFs were used to elaborateon the several challenges within drilling and wireline operations. Thechallenges were highlighted under such elements as environment,displays and controls, task demands and characteristics, instructionsand procedures, socio-technical, individual and stresses. In order toimprove human performance within drilling and wireline operations, anunderstanding of factors that have a critical effect on daily operations

performed by drillers and wireline operators is required. By providingthis information, it is assumed that organizational practices andmanagerial attitudes toward a safe and productive workplace are

reviewed so that proactive measures can be implemented to achievebest performance. The paper shows that the management of relevantorganizations has a critical role and responsibility in this context.

In Article VII we have used Redmills (1997)30 theories related tohuman error causation paradigms together with the industry challengesrelated to the drillers and the wireline operators working situation82, 83and 84. Different aspects and challenges were identified by using thehuman error causation paradigms which include the engineering error

paradigm, the individual error paradigm, the cognitive error paradigmand the organizational paradigm. The different paradigms look at the

challenges in drilling and wireline operations from different points ofview. The drillers have challenges due to the design of the drillerschair, switches, display, and due to the large amount of information thatthey have to handle, analyze and respond to. The wireline operator haschallenges due to the design of the wireline cabin, communicationwithin the operator crew, and the number of procedures. Both the


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drillers and the wireline operators working situation includes timepressure, limited supervisors training , limited time and motivation toconduct the safe job analyses (SJA). The paper presents the challengesand discusses what can be done to improve the drillers and wireline

operators working situations. This has specific benefits from a safetyand well integrity point of view, given the complex and dynamic natureof work performance.

Article VIII presents an overview of drilling and wireline operationsfrom an HTO perspective, particularly with reference to R. W. Baileys(1996)31 human performance model. The intention was to underlinespecific challenges in a sensitive work environment in offshore oil andgas production systems that have a large potential to pose some seriousthreats to the health, safety integrity, and work performanceefficiency82,83,84. The driller is exposed to some challenges related tothe human, the activity being performed and the context in which it is

performed. The drillers work situation and his level of interaction with

the operational set-up are quite demanding and complex. The wirelineoperators, on the other hand, also experience a number of challenges,

but quite different from those of the driller. The paper uses the humanperformance model to elaborate the complex interactions, as well as to

get an interesting overview of this complex work setting. On the otherhand, it provides a basis with the intention of improving performance.There are a large number of unforeseen factors that have a criticalinfluence on the work performance by the operators and crews incomplex work settings, such as drilling and wireline operations. A

proper knowledge of such complex work settings, from an HTOperspective, and further analysis with respect to dynamic connectionsbetween the personnel, the activity, and the context, can give the drillerand the wireline operators a better working environment and anopportunity to improve their performance without being exposed tohidden risks.


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Contents

Preface ................................................................................................... v

Scientific EnvironmentsCo-authors .............................................. vii

Summary .............................................................................................. ix

Contents ............................................................................................... xv

Part I .................................................................................................... 17

1 Introduction ............................................................................ 17

1.1 Scientific contribution .............................................................. 20

2 Well integrity .......................................................................... 23

2.1 Well integrity cases and surveys .............................................. 24

3 Barriers ................................................................................... 35

3.1 What is a barrier? ..................................................................... 35

3.2

Well barrier .............................................................................. 36

3.3 Robust well barrier elements .................................................... 403.3.1 Why is the tubing and casing leaking? .............................................. 40

3.3.2 Well cement - What can be done to improve cement integrity? ......... 48

3.3.3 BOPWhat can be done to improve well integrity? ......................... 49

3.3.4 GLV and ASVWhat can be done to improve well integrity? ........... 51

3.3.5 Other well barrier elements ............................................................... 53

4 Well integrity status and human factors .............................. 59

4.1 Well integrity incidents and accidents ..................................... 59

4.2 How can human factors contribute to well integrity? .............. 634.3 Well integrity status on NCS .................................................... 71

5 Methodology ........................................................................... 75

6 Results ..................................................................................... 81


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6.1 Summary of Article I ................................................................ 81

6.2 Summary of Article II .............................................................. 85

6.3 Summary of Article III ............................................................. 88

6.4 Summary of Article IV ............................................................. 93

6.5 Summary of Article V .............................................................. 96

6.6 Summary of Article VI ........................................................... 100

6.7 Summary of Article VII ......................................................... 102

6.8 Summary of Article VIII ........................................................ 105

7 Limitations ............................................................................ 111

8 Conclusions and further work ............................................ 113

Appendix 1- Temporary abandoned wells ......................................... 119

9 References ............................................................................. 127

10 Abbreviations ........................................................................ 139

Part II ................................................................................................ 141

List of Articles ................................................................................... 141

Article I .............................................................................................. 143

Article II ............................................................................................ 167

Article III .......................................................................................... 185

Article IV ........................................................................................... 217

Article V ............................................................................................ 243

Article VI ........................................................................................... 277

Article VII ......................................................................................... 305

Article VIII ........................................................................................ 335


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Part I

1 Introduction

Well integrity is defined in NORSOK D-010 as an application oftechnical, operational and organizational solution to reduce risk of

uncontrolled release of formation fluids throughout the life cycle of the

well. Well integrity has also been defined as The instantaneous stateof a well, irrespective of purpose, value or age, which ensures the

reliability of the barriers necessary to safely contain and control the

flow of all fluids within or connected to the well60. BG Group65describes well integrity thus: to operate the wells under known,

specified conditions, in such a way that the risk of equipment failure,

endangering the safety of personnel, the environment and asset value is

as low as reasonably practical (ALARP). According to Tobi (2005)92,technical integrity occurs when the asset is designed, operated,maintained and abandoned while keeping the risk of failure over its life

cycle as low as reasonably practicable (ALARP). There is not a

common global definition of well integrity, but the NORSOK D-010definition is widely used64.

Well integrity means to have the barriers in place, understand andrespect them, test and verify them, monitor and maintain them and havecontingencies in place when or if the barriers fail during the life cycleof the well. Well integrity is a complex issue, and well integrity

problems can occur in different phases of the wells life cycle such asduring construction, production/injection, intervention or abandonment.The integrity problems can include both formation-induced problems61and operational problems. Well integrity can be divided into different

operational sequences like drilling, completion, production, wellintervention, and temporary and permanent plug and abandonment(P&A). The main phases6 where the leakage can be discovered areduring the initial test and verification, production and injection(continuous monitoring of annulus pressure) or during routine leaktesting of equipment such as down hole safety valve (DHSV), annulus


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safety valve (ASV) or gas lift valve (GLV). Leakages can occur duringthe installation phase or after installation of the completion equipmentdue to casing wear, malfunctioning equipment or insufficient testing

procedures. Operational changes61 can affect the pressure andtemperature level in the well during start-up of gas or water injection,changed oil production rate or closing-in the well which can lead toleakages due to thermal and pressure load cycles on the wellconstruction. Leakages and degradation of well barrier elements canoccur due to corrosion, erosion, fatigue, wear, pressure, loads andtemperature cycles. The industry has experienced well integrity issues

in well barrier elements such as cement, tubing, casing, blow outpreventer (BOP), wellhead, Xmas tree, or in completion equipmentsuch as production packer, PBR, seal stem, ASV or GLV.

Well integrity60 is fundamental during the life cycle of the well, andwell integrity should be the heart in the well integrity managementsystem. The well integrity management system should identify the

potential hazards that can occur during the different phases of the well.Properties such as pressure, temperature, fluids, particles, formation

porosity, permeability, faults and unconformities are factors that caninfluence well integrity. The International Regulators Forum (IRF)77

has expressed expectations related to management of the well integritywhich include: management, leadership and integrity performanceindicators1,59. The companies should have effective management ofintegrity data and perform continuous monitoring, inspections andaudits during the lifetime of the asset and the wells. The companiesshould use appropriate design standards, maintenance managementsystems and clear management of change procedure. The IRF isfocusing on cross-industry training and learning, risk assessment toolsand procedures, competent and trained workforce with knowledge andunderstanding of the barriers at all levels.

The well integrity categorization should be included in the performanceindicators for all operating companies together with the other HSEperformance indicators such as serious incidents, falling objects andtotal recordable injury frequency to increase the focus on well integrity

problems and the reasons to prevent major accidents. There are severalincidents and accidents showing that the oil and gas industry has to


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further focus on well integrity, barriers and well barrier elementsfunction, qualification and verification including long-tem integrity.These aspects needs to be included in all well phases from design to

permanent plug and abandonment (P&A), and in all well operationssuch as drilling, production, injection, well intervention, plugging andabandonment. The Snorre29,69 incident and the Montara60 andMacondo76 accidents are good examples showing the need to focus onwell integrity in all phases of the well.

Well integrity6 is an issue affecting the entire life cycle of a well toprevent uncontrolled release of formation fluids through technical,operational, and organizational barriers. Well integrity is affected bythe human element, the technology and the organization (HTO)58. Thehuman element has to handle situations related to competency,responsibility, manning, training, communication and team work,operational tasks, planning, transfer of experience and time limitations.The technical element has to handle the equipment and technology andsituations related to well design and limitations, operations, operationaltasks, and reservoir behaviour. The organizational element has tohandle situations related to procedures and standards, responsibility andleadership, organization and manning, competency and training,

communication and team work, planning and experience of exchange.The human performance model31 gives an overview of the complexwork setting and helps to spot the critical influence factors that mayhave a large potential to contribute to safety and work performancerisks. There are unforeseen factors that have a critical influence on thework performance by the operators and crews in complex worksettings. But proper knowledge of such complex work settings, from anHTO perspective, and further analysis with respect to dynamicconnections between the personnel, the activity, and the context, cangive a better working environment and an opportunity to improve thehealth, safety integrity, and work performance. The understanding of

the interaction between HTO, the knowledge about performanceinfluencing factors30 (PIFs) and error causation paradigms30 may becritical to achieving the goals of safe and effective well operations. Theerror causation paradigmsare used to spot the critical influence factorsthat have a large potential to contribute to safety and work performancerisks. The identified challenges with respect to the four paradigms30


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(engineering, individual, organizational and cognitive) need to bediscussed in relation to what can be done to improve the workingsituations which can have benefits from a safety and well integrity

point of view, given the complex and dynamic nature of workperformance. The thesis shows that there are different ways of lookingat the drillers and wireline operators working situations 82,83,84 (e.g.human performance model, PIFs or error causation paradigms). It alsoshows that these methods can be useful during audits to identify workrelated challenges.

1.1 Scient i f ic con tr ibut io n

The purpose of the work presented in this thesis is in general to presentthe methods for analyzing, evaluating and communicating the wellintegrity challenges, trying to find the solutions for why the wellintegrity challenges occur in order to improve well integrity in thefuture. The work performed is based on projects and audits performed

by the Petroleum Safety Authority and the University of Stavanger.

The thesis is a contribution to increasing the focus on well integrity androbust well barriers in a life cycle aspect. Several projects and audits

are performed to identify the well integrity challenges on the NCS inthe production wells (including production wells with gas lift),injection wells (including CO2 injection and adjacent wells),multilateral wells and temporary abandoned wells. The thesis alsoincludes a well integrity survey in the Netherlands and some workrelated to increasing the focus on permanent plug and abandonment.

All papers included in Part II have been, or will be, published ininternational journals or at acknowledged international conferenceswith referees. This is a way of documenting the scientific level of thework. The work presented in the thesis contains something new,

original and solid. Paper I presents one of the first well integritysurveys performed on the NCS. This survey was performed by the PSAin 2006 and has led to industrial well integrity involvement as adevelopment of the Norwegian Oil Industry Association (OLF) wellintegrity forum (WIF), OLF well integrity Guideline Number 117, wellintegrity engineers, increased focus on well integrity competence and


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training, exchange of well integrity experience, handoverdocumentation, well barrier schematics, well integrity categorization,well integrity management systems and an increased focus on wellintegrity in a life cycle aspect. Paper III presents the first well integrityinspection supervisory activity performed in the Netherlands based onthe industry standard NORSOK D-010 where the PSA assisted theSupervision of Mines Netherlands (SSM). The survey identified areasfor improvement related to well integrity personnel competency,document control, management system, well design criteria, conditionmonitoring, well handover and experience transfer. The findings were

similar to the findings on the NCS in Article I, but the survey did notachieve the same effect as on the NCS. The work presented in thisthesis contributes to further development of robust well barriers in a lifecycle aspect. Paper II presents the reasons for well integrity issues ininjection wells on the NCS, and it has contributed to increased focus onwell design of the injection wells related to temperature effects and theselection of completion equipment, and improved monitoring of theoxygen level in the injected water. Paper IV presents the well integritychallenges in the CO2 injection wells and the adjacent wells. It hascontributed to increasing the focus on well integrity and well design ofthe injection wells and the adjacent wells including regulations and

standards, material selection, temperature effects, seismic surveys,cement products and cement operations related to long-term integrity.

Paper V presents some of the International Organization forStandardization (ISO) and American Petroleum Institute (API)standards that the petroleum industry uses to qualify well barrierelements. The paper has contributed to increasing the focus on how toqualify a well barrier element related to the acceptance criteria,including the exposed medium, temperature and long-term integrity.

Paper VI identifies the critical performance influencing factors (PIFs) 30

within drilling and wireline operations based on the experience fromPSA projects and audits82, 83, 84. PIFs affect human performance, humanabilities to perform actions in a safe and efficient manner and humanability to improvise and improve work. The paper has contributed toincreasing the understanding of the interaction between HTO and theknowledge about PIFs in order to achieve the goals of safe and


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effective drilling and well operations. In Paper VII we present humanerror causation paradigms30 together with the challenges in drilling andwireline operations82,83,84. The human error causation paradigmincludes the engineering error paradigm, the individual error paradigm,the cognitive error paradigm and the organizational paradigm. The

paper has contributed to looking at the challenges in drilling andwireline operations from different points of view by using the different

paradigms, and identifying the points for improvement from a safetyand well integrity point of view. Paper VIII presents an overview ofdrilling and wireline operations from an HTO perspective by using the

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to underline specific challenges related tothe dynamic connections between the human, the activity beingperformed or the context in which it is performed82,83,84. The papercontributes to providing an overview of this complex work setting andto spotting the critical influence factors that have a large potential toadd to safety and work performance risks. The presented workcontains something useful and relevant. All papers are based on datagathered from wells on the NCS and present the industrys challengesrelated to well integrity on the NCS in order to contribute to increasingthe focus on well integrity challenges in a life cycle aspect and tocontribute to the transfer of experience.


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2 Well integrity

Well integrity is defined in NORSOK D-010 as an application oftechnical, operational and organizational solution to reduce risk of

uncontrolled release of formation fluids throughout the life cycle of the

well. The life cycle aspect includes the phases from design to after thewell has been permanently plugged and abandoned,15 and all activitiesduring the life cycle of the well shall be carried out in a safe and

prudent manner. Well integrity can be divided into different operationalsequences like planning, drilling, completion, production, plug andabandonment (P&A). The potential use for the well should beconsidered during the well design phase including artificial lift and wellconverting, well operations, maintenance and abandonment. The well

barriers shall be designed, manufactured and installed to withstand allloads they may be exposed to and to maintain their function throughoutthe life cycle of the well. Materials should be selected to withstand theloads and environment they may be exposed to. The operational limitsneed to be defined and evaluated during the life cycle of the well. Theoperational limits could be related to the temperature, pressure, flowrate or the installed equipment limitations. The operational limitations

should also consider the effects of corrosion, erosion, wear and fatigue.The status of the well barriers should be monitored, tested, verified andmaintained through the wells life cycle, and the barrier conditions shall

be known at all times. There shall be sufficient independence betweenthe well barrier elements and if common well barrier elements exist,then a risk analysis shall be performed and risk reducing/mitigationmeasures applied to reduce the risk to as low as reasonably

practicable6. An emergency preparedness strategy and procedures shallbe established for all phases of the wells life cycle to describe how tohandle situations of hazard and accidents such as loss of well barriersand blowout.If a barrier fails, no other activities shall take place in the

well than those intended to restore the barrier and it shall at all times bepossible to regain well control by performing intervention work or bydrilling a relief well6, 15. Each operator on the NCS shall have a systemto manage the integrity of its wells and the critical parameters should

be easily available in order to document compliance with regulationsand standards 1, 6, 15, 65.


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Well integrity is a complex issue, and well integrity problems can occurin different phases of the wells life cycle, such as during design,construction, production, injection, interventions, testing andabandonment. Integrity problems can include formation-induced

problems61 such as pressure, temperature, formation fluids (flow rate,chemistry, sand and particles) which can result in material erosion,corrosion and degradation due to formation fluids or injected fluids.Operationally-related well integrity problems can also occur, such asoperating the well and equipment above the design limits, lack ofmaintenance, installation failures, equipment failures, and failures

related to testing and verifications or prolonged/extended lifetime. Themain phases in which the leakage can be discovered are during theinitial test and verification, during production and injection (withcontinuous monitoring of annulus pressure6) and during routine leaktesting of DHSV, ASV, GLV (if qualified as a well barrier element).Some leakages can occur during the installation phase or afterinstallation of the completion equipment due to casing wear,malfunctioning equipment and insufficient testing procedures.Operational changes can affect the pressure and temperature level inthe well during start-up of gas or water injection, changed oil

production rate or closing-in the well. These are situations that can lead

to leakages due to the thermal and pressure load cycles on the wellconstruction61. Leakages may occur through the cement, casing andcompletion equipment such as the packer, PBR, seal stem, annularsafety valve (ASV) or the gas lift valve (GLV)4.

2.1 Well integri ty cases and surv eys

Well integrity cases form 2003-2004A number of case studies were performed by the Norwegian PetroleumDirectorate (NPD) and Rock-Well Consultants in 2003-2004, and thestudies included well design cases from several operating companies on

the Norwegian Continental Shelf (NCS)17,18,19,20,21,29,55. The mainfindings in all the cases were an industrial need to improve competencein well design, well barriers and quality control both for the equipmentand the executed operations. The cases identified shortcomings relatedto robust design, monitoring of the independent well barriers, wellcontrol procedures for all the operational phases of the well and


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challenges related to obtaining updated well design data and easyaccessibility. The cases show that the companies had to improve riskmanagement; they had to consider the potential consequences and the

probability-reducing measures. The cases illustrate the importance offocusing on rare events that can lead to major incidents. The casesshow that long-term effects were not sufficiently considered. The long-term perspective is an important aspect when planning, designing,

producing, intervening in or permanently plugging and abandoning awell in order to get a robust well design that can handle challengesduring the life cycle of the well.

Well integrity survey in UK10

The Under Water Group (UWG) performed a well integrity survey onthe United Kingdom Continental Shelf (UKCS) in 2005 which showedthat 10% of the wells had been shut in during the last five years

because of structural integrity issues. The survey included 18 operatorsthat were responsible for 6137 of the 9196 wells drilled on the UKCS.The main well integrity problems were related to tubing leaks and valvefailures. Other identified integrity issues were annulus pressures,connection failure, scale, wellhead growth and leaks in the Xmas tree.Age was the primary cause of the structural integrity failure which

included erosion, corrosion and fatigue together with poor design andintegrity assurance standards. Prolonged field life, including exceedingthe well design life, was believed to have led to an increased frequencyof integrity problems on the UKCS. The UWG reported that theintegrity problems will further increase, since later in the field life theindustry will experience an increasing level of water cut, heat treatingand gas lift.

Well integrity survey in Norway in 20064

The Petroleum Safety Authority in Norway (PSA) performed a wellintegrity survey in 2006 based on supervisory audits and requested

input from seven operators, 12 facilities and 406 wells. The surveyconcluded that 18% of the 406 selected wells had well integrity issuesand 7% of the wells were shut in. The identified well integrity problemswere in well barrier elements such as tubing, annulus safety valves,casing and cement because of corrosion, erosion, temperature effects ordesign issues. The well integrity challenges were related to well


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documentation, handover documentation, regular condition monitoring,application of NORSOK D-010, consistent practice within thecompany, management of change, competence and training, opennessand exchange of experience, reliability analyses and performanceindicators. The results from the survey indicated a relatively lownumber of reported well integrity failures in subsea wells, and indicatedthat this can be explained by the limited possibility to monitor thesewells.

Well integrity inspection project in the Netherlands

The well integrity inspection project

11

was initiated and executed by theSSM drilling & well technology discipline in the Netherlands withassistance from the PSA Norway and consultants from Wellbarrier forspecific well barrier schematic analyses in 2008. The project was basedon supervisory audits and requested input from 10 operators and 31wells. The project indicates that 13% of the selected wells had wellintegrity failures, issues or uncertainty, and 3% of these were shut indue to integrity issues. The survey concludes that 4% of the productionwells (1/26) and 60% of the injection wells (3/5) had well integrityfailures, issues or uncertainty. This is only to a certain degreerepresentative of the well status in the Netherlands. The data limitation

in this project is caused by the limited number of wells being selected.Even with this limited number of wells being investigated, theconclusion remains that a number of challenges related to well integrityexists. The discussions in the clarification meetings supported thefindings. It was evident from the operators experience that these wellintegrity challenges were representative in the larger range of wells.

Well integrity survey in injection wells on the NCSWell integrity surveys performed by Statoil, Sintef and the PSA showthat the injection wells are almost twice as likely to leak as productionwells on the NCS4,7,8,9. Statoil8 performed a company internal well

integrity survey in 2007. The Statoil well integrity data shows that 20%of 711 wells had well integrity failures/issues or uncertainties. Thesurvey concluded that 17% of 526 production wells and 29% of 185injection wells had well integrity issues. Sintef9 performed wellintegrity studies for one operator, including eight fields and 217 wellson the Norwegian Continental Shelf (NCS). The studies showed that


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19% of the producers and 37% of the injectors had well integrityproblems. The study included analyses of the leak history from 1998-2007, and the identified leakages occurred in the wellhead, tubing toannulus A, down hole safety valve, annulus A to B, and annulus safetyvalve. The analyses showed that the gas lift wells experienced leakageafter an average of two years of operation after gas lift was introduced.The wells on gas lift were designed for dry gas, but the operationalconditions were wet gas and more corrosive CO2 than the well designcriteria. The studies concluded that the wells had been operated outsidethe design envelopes, which leads to reduced well lifetime.

The PSA7 performed a survey to investigate the possible mechanismsof well integrity challenges on the NCS related to injection wells in2008. This study represented six operators and included water injectors,gas injectors, and water alternating gas (WAG) wells. The studyshowed that the integrity problems and the barrier failures were relatedto the completion design, the injected water and design of the WAGwells.The completion design includes a seal stem and a PBR (polished

bore receptacle). This design has a dynamic seal between the tubingand annulus. A high differential temperature between the water beinginjected and the reservoir resulted in a significant movement of the seal

stem within the PBR. Historically, these wells have shown that thiscauses leaks over time. The integrity problems were also related to theinjected medium. The operators detected corrosion and leakage intubing and completion equipment due to a high level of oxygen in theinjected water in relation to the steel grade and the use of variation ofsteel grade in the same well. Integrity problems were identified in thewater alternating gas (WAG) wells related to leakage in the tubinghanger seal, connections and production packers because oftemperature cycling. Leaking threads in tubing connections may exist

because of running, handling, and installing the tubing connections. Inaddition, the selection of materials, packer fluid and lubricants can have

an influence on the equipments integrity.

Well integrity in CO2 wells and adjacent wellsCO2 capture and storage (CCS) can be a contributing factor in reducingthe release of greenhouse gases to the atmosphere. In order toimplement CO2 injection and storage on a widespread scale, work


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needs to be done to further adopt an appropriate framework, regulationsand standards, and it is important to include the adjacent wells in theseconsiderations. Adjacent wells were defined as wells that can beexposed to the injected CO2. A CO2 injection reservoir may be

penetrated by a number of adjacent wells that can be potential leakagesources. These wells can be abandoned-, production-, injection- ordisposal wells. Adjacent wells can have well integrity issues that canlead to leakage of CO2 to the surroundings. The wells that penetrate theCO2 injected reservoir should consider CO2 resistant design since theyhave the potential of exposure to CO2. A CO2 resistant design includes

considerations related to CO2-resistant -cement, -casing, -tubing, -packers, and other exposed down hole and surface equipment. There isno common industry practice related to the design of temporary and

permanent plug and abandonment of CO2 injection wells and adjacentCO2 injection wells.

The main challenge with regard to CO2 storage is the integrity of theCO2 injected reservoir and the verification methods of the structuralintegrity. Seismic surveys are performed to verify how the CO2medium moves within the reservoir. The uncertainty related to seismicsurveys is dependent on the storage depth, and whether the CO2

injected medium is in gas, liquid, or aqua phase. There are uncertaintiesrelated to how the CO2 medium is spread within the reservoir, and thiscould have an impact with regard to the integrity and degradation of theconstruction of the adjacent wells.

The CO2 injected reservoir and the integrity of the caprock can beaffected by the injected medium and the buoyancy forces. The caprockis required to create overpressure, and there are several mechanismsthat can create overpressure, but the buoyancy forces are considered asa dominating mechanism that is always present in the reservoir5. The

buoyancy force can be explained as the lightest fluid moving to the top

and the heaviest fluid to the bottom. An example illustrating this iswhere standardized pore pressure is about 1.03 sgon the NCS, and theinjected CO2 are about 0.5-0.9 sg which will result in a non-balanced/equilibrium situation where the density contrast/differential and

buoyancy factor will press the CO2 medium to the top of the reservoir.This force may increase the probability of leakage trough micro annuli


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and fractures in the caprock. The relatively high buoyancy force andthe large volumes of injected CO2 result in an extensive area that must

be considered for the potential of CO2 leakage, i.e. through abandonedwells, cement micro annuli or reservoir fractures. The placement of theCCS reservoirs has to be analyzed due to the risk of caprock leakage,and the selected reservoirs should have several barriers against leakageto the atmosphere. Dehydration of shale formation in a CO2environment is also an aspect that needs further work related to thelong-term integrity of the injected reservoir5.

There are examples of injected CO2

leakage trough adjacent wells108.The CO2 medium went from the injected reservoir and through theadjacent well due to integrity problems in the adjacent well. Theindustry has experienced challenges in the CO2 injection wells relatedto the CO2 fluid and degradation of the elastomers, but there is littleinformation published related to elastomers behavior in a CO2

environment, and this may be a subject that needs further work87.

NOTE: If the NORSOK D-0106 well integrity standard shall include CO2 injectionand adjacent wells in the future, the definition of well integrity can be changed toinclude an application of technical, operational and organizational solution toreduce risk of uncontrolled release of formation fluids or injected medium throughout

the life cycle of the well.

Well integrity in multilateral wells

Multilateral wells73 are described as a single well with one or morewellbore branches radiating from the main borehole. The multiple wellsare drilled from a single main wellbore, and the technology is thereforeeliminating rig days for drilling the upper hole sections for each welland saving well slots. The multilaterals can access several reservoirzones from branches of a single wellbore which gives the ability toreach widely spaced reservoirs. The multilateral wells are classified bythe technical advancement of multilaterals73 (TAML) from Level 1 to

Level 6 according to the complexity of the junctions. Level 1 is thesimplest open hole junction completion, while Level 6 is the mostcomplex completion with pressure integrity at the junction.

Some technical challenges have been identified in multilateral wells onthe NCS74,75 related to degradation of well barrier elements, well


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control and drilling fluid capacity, as well as design and challengesrelated to intervention. Casing wear73, 74 can occur in long-reach wellswith a relatively high exposure time to rotating drill pipes. Casing wearcauses a reduction of the casing wall thickness and changes in thecross-section shape from circular to oval. Oval casing can lead to

production packer setting problems, reduced packer seal ability due tothe limited tolerance, and micro leaks around the packer. The highcasing wear leads the operator to use carbon steel in the production

packer setting area and this situation can give rise to challenges relatedto CO2 corrosion (from the gas lift) and galvanic corrosion over time

73,

74

. Well control and drilling fluid capacity were identified as achallenge since operations like pulling temporary casing plugs andwhipstocks require sufficient contingency kill mud available due towell loss situations73, 74. The rig has a minimum of one well volume ofmud, which means that the operator is s dependent on mud supplied byship if critical well control situations occur. The well design73, 74includes the casing between annulus A and B to be drilled open due tothermal effects and pressure increase in the closed annulus B. Thechallenge is related to the fact that there is only an annulus A betweenthe tubing and the formation. The cement quality can be improved andthe identified challenges were related to filter cake, circulation,

centralization and losses to the formation. Challenges have also beenidentified related to the pressure integrity junction, since themultilateral (MLT) junction and the MLT deflector cannot be pressuretested. The completion design includes a multilateral intelligentcompletion interface that limits the access to the multilateral branchesof the well73, 74. The production from each of the legs and pluggingcannot be performed individually on each branch.

Well integrity in temporary abandoned wells

The PSA, Sintef and Wellbarrier have performed a survey related totemporary abandoned wells on the NCS in 2011 which presents some

industrial well integrity challenges116,117,118. Temporary abandonedwells are defined as: all wells/all wellbores except all active wells andwells that are permanently plugged and abandoned according to the

regulations. Active wells are defined as production-/injection wells that

are currently producing or injecting and the survey includes both

platform wells and subsea wells116. There are 193 wells from eight


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companies included in the survey. The results from the survey showedthat about a third of the temporary abandoned wells had well integrity

problems of one form or another. The survey showed that there are 1%(2/193 wells) in category red, 8% (15/193 wells) in category orange,29% (57/193 wells) in category yellow and 62% (119/193 wells) incategory green; see Appendix 1 for more information. The PSA willfurther focus on reducing the number of temporary abandoned wells.Hence, the operator wells in category red and orange should be takencare of ref. Activity Regulations 85 regarding well barriers: If abarrier fails, activities shall not be carried out in the well other than

those intended to restore the barrier. The survey showed that wellshave been temporarily abandoned since 1970. There are 27 wells onthe NCS that were in a state of temporary abandonment prior to 2000,and three of these wells have mechanical plugs as the primary

barrier117. The survey concluded that the operators need to define whatis meant by temporary abandonment. One solution to this problemcould be to use the well integrity categorization1 of the temporary wells(red, orange, yellow and green) and define the number of months oryears each category can be temporarily abandoned. Another solution isto define the exact number of months or years the wells can betemporarily abandoned.

NORSOK D-0106 standard presents different requirements forpermanent P&A and temporary abandoned wells related to thepermanent well barriers and the plugging design. An example showingsome differences is as follows: a mechanical barrier may beacceptable for temporary abandonment but a mechanical barrier withelastomer seals are not acceptable as a permanent well barrier.Mechanical barriers are not suited for long-term abandonment ref.Activities Regulations Section 88 securing wells15: All wells shall be

secured before they are abandoned so that well integrity is safeguarded

during the time they are abandoned. Facilities Regulations Section 48

regarding well barriers15 states that When a well is temporarily orpermanently abandoned, the barriers shall be designed such that they

take into account well integrity for the longest period of time the well is

expected to be abandoned. The well integrity situation in temporaryabandoned wells on the NCS shows that the industry needs to performsome further work related to defining the future plans, improving well


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integrity and possibly implementing P&A for a number of these wells.The survey also showed that the operators should follow the minimumrequirements for well barrier schematics in OLF Guideline Number 117about well integrity116,117,118 and perform monitoring of the subsea wellsrelated to well integrity, if the plan is to abandon the wells for morethan twelve months, according to Activity Regulations Section 88about well integrity.

Well integrity in P&A wells

There are about 500 offshore installations on the NCS and

approximately 2200 wells to be permanently plugged and abandoned

97

.This challenges both license owners and authorities to look forsolutions to perform the P&A of wells in a robust and safe manner. Theindustry is talking about a big wave of permanent plug andabandonment of wells in connection with field decommissioning whichmeans a huge number of wells need to be plugged and abandoned in thefuture. Statoil97 has about 1100 wells that at some point need to beabandoned.

The P&A Forum (PAF) was established in November 2009, followedby the Drilling Managers Forum (DMF) and facilitated by The

Norwegian Oil Industry Association (OLF). The P&A Forums purposeis to generate common industry understanding of P&A regulationsand challenges and to contribute to improving P&A and slot recovery

competence to ensure robust well integrity. The P&A Forum membersare ConocoPhillips, Statoil, BP, Det Norske, Norske Shell AS, CentricaEnergy, Total and Talisman; and the PSA are observers in the forum97.

Permanent plugging and abandonment includes the material, placementand monitoring. The requirements are current in the wells lifetime thatmeans time in use and time subsequent to permanent plugging andabandonment(P&A)15. The Facility Regulations Section 48 about well

barriers describes the well barriers to be: designed such that wellintegrity is ensured and the barrier functions are safeguarded during

the well's lifetime, When a well is temporarily or permanently

abandoned, the barriers shall be designed such that they take into

account well integrity for the longest period of time the well is expected

to be abandoned.


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The Activity Regulations Section 85 about well barriers15 describes the

well barriers during well activities to be tested with sufficient

independence. If a barrier fails, activities shall not be carried out in the

well other than those intended to restore the barrier.

There are no specific methodologies to evaluate well integrity afterpermanent well abandonment, and the existing guidelines related topermanent well abandonment are intended for oil and gas wells and notfor CO2 injection wells and adjacent wells. NORSOK D-010 standarddoes not present a primary and secondary barrier envelope in a P&Awell; the standard defines two barriers (cross-section barriers) againstnon-permeable formation and three barriers (cross-section barriers)against permeable formation. Some industrial challenges have beenidentified related to P&A, since the permanent barriers may be difficultto achieve and the industry is selecting different solutions for failure inthe annulus barriers. Casing milling is performed and casing

perforations are made to place cement in the annulus; both methodsdegrade the barriers since they will just include the cement and it isdifficult to achieve good cement jobs, tested and verified, in theseoperations. There are no requirements for re-logging of the cementintegrity when a well is to be permanently abandoned, which means

that it is dependent on cement evaluations from when the well wasconstructed. NORSOK does not prescribe the guidelines for monitoringabandoned wells, but it is important that the permanently abandonedwells (including CO2 wells) are monitored for potential leaks.


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3 Barriers

3.1 What is a barrier?

The Management Regulations Section 5 about barriers15State: Thebarrier (physical or non physical or a combination) shall be

established to a) reduce the probability of failures and hazards and

accident situations developing, b) limit possible harm and

disadvantages. When more than one barrier is necessary, there shall be

sufficient independence between barriers. Barriers are defined in ISO

1777698

as a measure which reduces the probability of triggering ahazard's potential to cause damage or reduces the damage potential .Eiane (2009)36 defines a barrier as a mechanism concrete or abstractthat shall prevent an unwanted situation from occurring. The industryuses different names related to barriers15, and barriers are oftendescribed as: safety barriers67, 85, safety functions15, 68, 86, safetysystems79, 86, safeguards15,protective systems, defenses81, protections,or layers. The barriers main function85 is to prevent, control, andreduce losses or mitigate undesired or accidental events. The barrierscan also be described as the safety margin, allowing the company to

perform petroleum or other activities.

A barrier consists of one or more barrier elements85, and the elementscan be of different types; there can be technical, operational,organizational or human components in a barrier system. The barrierscan be defined in series and in parallel, as primary and secondary6,temporary and permanent6, active and passive79, soft and hardapplications81 or physical6 and non physical67, 85. The independency15

between the different barriers and the quality79 of the barriers areimportant aspects in the long term. The qualification process of the

barrier is performed as with other functional equipment, and thequalified barriers need to be regularly inspected, monitored, tested,

verified and maintained in order to function properly. The barriersperformance15, 85, 86 is dependent on the qualities of the barrier: itscapacity, reliability, accessibility, functionality, efficiency andmobilization time, its ability to withstand loads, its integrity androbustness, its vulnerability and the competence of its personnel.Humans can be part of a well barrier60, since the selection and


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installation of effective well barriers requires competent personnel withexperience and knowledge who can understand the potential hazardsand how to test the selected solution by including the life cycle aspects.The organization needs to train, develop and manage competentindividuals who can work in organizational structures to improve thehuman barrier.

3.2 Well barr ier

The well barrier is defined in NORSOK D-0106 as an envelope of one

or several dependent well barrier elements preventing fluids or gasesflowing unintentionally from the formation, into another formation or

to surface and the well barriers shall be designed to ensure wellintegrity during the well's lifetime15. The well barriers shall bedesigned to prevent unintended influx and outflow to the externalenvironment and designed so that their performance can be tested andverified 6, 15, 60. The well barrier can be defined in series or in parallel,as primary or secondary6, temporary or permanent6, active or passive,or as physical or non-physical. The well barriers shall be designed,manufactured and installed to withstand all loads they may be exposedto and maintain their function throughout the life cycle of the well 1.

Materials and functions should be selected to withstand the loads andenvironment to which the well barrier may be exposed1, and thephysical location and the integrity status/conditions of the barriers shallbe known at all times6. The well barrier design should not beconstructed so that one single failure of a well barrier or well barrierelement leads to uncontrolled outflow to the external environment. TheHealth, safety and environment (HSE) regulations refer to a robust welldesign15 which may include the possibilities to re-establish or replace alost well barrier6. The well barrier includes one or several well barrierelements (WBE), and the technical and operational acceptance criteriafor each WBE are defined in NORSOK D-0106. Some examples of

well barrier elements are: drilling fluid, packers, cement, casings,mechanical plugs, blow out preventers, wellheads, casing hanger sealsand Xmas trees.


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Figure 1: NORSOK D-010 and well barriers

NORSOK D-0106 defines the primary and the secondary well barrier asbeing independent of each other which means without common wellbarrier elements (WBE). If there are common WBE then a risk analysis

and risk reducing/compensating measures have to be performed toreduce the risk as low as possible (ALARP)6. The well barriers areillustrated in the well barrier schematics (WBS)6. The primary well

barrier6 (blue) illustrates the normal working stage, which for somesituations is the fluid column or a mechanical well barrier that

provides closure of the well barrier envelope and the secondary wellbarrier6 (red) illustrates the ultimate stage, which in most casesdescribes a situation where the shear ram/shear valve is closed.

Degradation, leakage or lack of primary and secondary well barrier canalso be illustrated by the Swiss cheese model80.


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Figure 2a: Drilling6 Figure 2b: Production6 Figure 2c: Wireline6 Figure 2d: P&A6

NOTE: all WBS include a note field in NORSOK D-010.

Figure 2a is a well barrier schematic of a well during drillingoperations. The fluid column is the primary well barrier and the casingcement, casing (last casing set), wellhead, high pressure riser (ifinstalled) and the drilling BOP is the secondary well barrier duringdrilling operations6.

A well barrier schematic during production is illustrated in Figure 2b.The schematic presents a well that is capable of flowing which is shutin. The primary well barrier includes the production packer, the

completion string (the tubing between the DHSV and productionpacker) and the DHSV. The secondary well barrier includes the casingcement, casing, wellhead (casing hanger, tubing head with connectors),tubing hanger, annulus access line and valve and the production tree6.


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Well barrier schematics of wireline operations performed through thesurface production tree are shown in Figure 2c. This presents in bluecolors the primary well barrier which includes the casing cement,casing (below the production packer), the production packer,completion string, tubing hanger, surface production tree, wirelineBOP, wireline lubricator and the wireline stuffing box/grease head. Thesecondary well barrier includes the casing cement, casing, wellhead(including casing hangers and access lines with valves), tubing hanger,surface production tree and the wireline safety head. The figure

presents common well barrier elements and some risk-reducing

measures

6

.Well barrier schematics of a perforated well during permanentabandonment are presented in Figure 2d. Liner cement and the cement

plug (across and above the perforations) are defined as the primary wellbarriers. The secondary well barrier includes the casing cement, cementplug (across the liner top). The WBS includes the casing cement andthe cement plug (inside and outside the tubing) if the tubing is left inthe hole. The permanently abandoned wells also have open hole tosurface well barrier that includes the cement plug and the casingcement (surface casing)6.

NORSOK D-0106 Section 15 describes the well barrier elementsacceptance criteria, including how to perform the initial test andverification. These tests include leakage test, pressure test and averification of the well barrier element. The leakage test includes a low

pressure test of 15-20 BAR for five minutes and a high pressure test ofmaximum anticipated differential pressure that the WBE will beexposed to for a minimum of 10 minutes. The acceptable leak ratesshould be zero, unless other values are specified. When handing overwells, the barrier status shall be tested, verified and documented1, 6, 15.The handover applies when handing over the well from one

organization to the other (from drilling to operation), and from shift toshift at crew change. Handover from company to another is notincluded. The NORSOK D-0106 and OLF Guideline 1171 describewhat information is to be transferred in the handover documentation,and how this should be done. The handover documentation contains1,4,6well construction information, well barrier schematic, completion


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schematic, handover certificate which presents the status of the valves,pressure and fluids, and the operational limitations.

3.3 Robust well barr ier elements

The requirements related to robust well barriers are described in theHSE regulations on the NCS15 relating to the design and outfitting offacilities in petroleum activities. The Facilities Regulations Section 5about design of facilities state: The Facilities shall be based on themost robust and simple solutions as possible, and designed so that:

they can withstand the loads, major accident risk is as low as possible,a failure in one component, system or a single mistake does not result

in unacceptable consequences, the main safety functions are

maintained, materials handling and transport can be carried out in an

efficient and prudent manner, a safe working environment is facilitated,

operational assumptions and restrictions are safeguarded in a prudent

manner, health-related matters are safeguarded in a prudent manner,

the lowest possible risk of pollution is facilitated and prudent

maintenance is facilitated.

The petroleum industry88 and well integrity6 are built on always having

robustness113

and redundancy (barriers, well barriers and well barrierelements) as safeguard/defenses to avoid release of formation fluid.This requires systems and procedures related to well construction,operation, monitoring and abandonment to prevent the unintendedescape of hydrocarbons. This requires the design of primary andsecondary barriers to secure the integrity of the well, barrier overviewand competence, maintenance, testing and verification, respect andunderstanding. PSA surveys4, 7, TecWel24 and major risk incidents overrecent years28, 60, 69, 76, 90 have identified the need to further analyze thereasons for well integrity issues in well barrier elements such as tubing,casing, gas lift valves, annulus safety valves, well cement and BOP.

3.3.1 Why is the tubing and casing leaking?

The tubing and casing premium connection41,44 are potential leak pointsin the well, and the industry knows that one connection can disqualifythe well string. The primary and secondary well barrier envelope can


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include 1000-1200 casing, liner and tubing threaded connections36 in atypical well on the NCS. If 99.9% of the well string connections aresealed then we may have a 100% well string failure and a disqualifiedwell string. The reliability of a premium metal to metal sealconnection40,54 can be compromised unless proper running andinstallation are performed, and the thread lubricants (dope), runningequipment, and computer controlled makeup equipment should beselected with regard to the reliability of the connections. There areseveral factors that can contribute to well integrity challenges andleakage in tubing and casing connections. The key to tubular integrity

lies in the accurate makeup process of their connection, testing andqualification, protectors, thread compounds (lubricants/dope), running,handling and installing connections, packer fluids and well stimulationfluids.

The life cycle aspect (cradle to grave)36 needs to be included in thedesign phase of the tubing and casing string. The design input has toinclude what the string shall perform, under which environmentalconditions and the lifetime of the string. The string has to be designedfor all the operational aspects that can occur during the tubing andcasing string lifetime, such as: running in hole, setting of packers,

pressure testing, well control incidents, well killing operations, wellintervention and pulling out of hole. The material selection needs to beevaluated in relation to produced/injected medium104, reservoir fluids,completions fluids100, 101, 102, stimulation fluids103, or other fluids thewell is exposed to. Other factors that need to be evaluated are pressure,temperature, loads, and the flow rates the string should handle on bothsides. The formation and the materials mechanical properties6, 37, 38, 59shall also be evaluated in the design phase. The analyses need to be

performed to reduce the risk of casing and tubing degradation orleakage because of corrosion, erosion, fatigue, burst, collapse,tension/compression or wear.

Tubing and casing testing and qualification

The industry qualifies the premium connections by using theinternational standard (ISO) 1367939, specific customer procedures andthe finite element analysis (FEA)57. ISO 13679 is an industry standardfor connection testing which defines four test classes of casing and


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tubing connection application levels (CAL) I-IV, of which CAL IV andIII are defined as primary and secondary well barrier elements. Theinternal test pressure media are gas in CAL IV, III, and II, and liquid inCAL I. The bake and thermal cycle temperatures are 180 oC (Cal IV)and 135 oC (CAL III), and the thermal cycling test minimumtemperature for all application levels shall be less than or equal to 52oC. Challenges have been identified in relation to using the connectionsin cold environments and in high temperature wells above 180 oC. Theindustry does use a thermal well casing connection evaluation protocol(TWCCEP) related to thermal well applications with temperature

intervals between 200-230

o

C, but this protocol does not overlap thetemperature level between ISO 13679 and the TWCCEP43, The ISO13679 standard addresses five types of primary loads to which casingand tubing strings are subjected in wells: internal and/or external fluid

pressure, axial force as tension/compression, bending includingbuckling/wellbore deviation, and makeup torsion. The test programincludes physical testing as makeup/breakout tests, load envelope testsand limit load tests. The standard ISO 1367939 does not address theoperational considerations and the loads such as rotation torsion, non-axis symmetric loads such as area, line or point contact loads, loadcycles, and testing related to vibration or fatigue. The standard does not

include the requirements related to long-term integrity testing of theconnections.

HandlingPipes coming from the mill can have defects if they have been badlystored or transported. The storage inspection shall cover the externaland internal coating condition, the external and internal body, threadconnections and seal inspection, dope condition, damage to protectorsand pipe marking. But it can be difficult to detect visually whether the

pipe is damaged.

Compounds (lubricants/dope)Storage and running compounds

The industry uses storage compounds40 to prevent the connections fromcorroding after they leave the factory. The storage compounds areseldom suitable for makeup, so connections with storage compoundsmust be cleaned and replaced by applying running compounds which


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prevent galling53during stabbing and makeup. There are some rules ofthumb to reduce the risk of integrity problems in tubing, liner or

casing due to compounds40. These are: never use barite or wire brushto clean the connections and never use cleaning agents that may leave

a film on the connections. Do not use contaminated thread compound

(liquids, solids particles, etc.) and do not allow the mud or

drilling/completion fluids to overflow the box connection when filling

up or running in hole. Apply the correct quantity of compound to all the

thread, seal and shoulder areas and apply thread storage compound on

returned pipe in case there is a delay in the restocking. The amount of

running compound can affect the makeup process. Too little compoundcan cause a high torque prior to the shoulder40, too much compound cancause bleed off36, and both situations can result in a second attempt atmakeup. The importance of using the correct thread protectors40 cannever be underestimated since incorrect protectors can fall off the pipeand lead to accidents. Thread protectors can be reused as long as they

pass performance tests which also include cleaning of the protectors.Failure related to the cleaning process can contaminate the connectioncompounds, lead to corrosion and damage the connections sealintegrity.

Dope free connectionsThere are dope free connections available25, 26, 27, 28, and the industryreports benefits related to environmental factors41, 45, 47, 51, 52 , easythread inspection, prevented thread cleaning, minimized yard and righandling, prevented plugging of formation pores and increasedefficiency for well intervention operations due to elimination of theexcessive dope in the well. The dope free casing and tubingconnections led to safe operations offshore and onshore as lesshandling was involved. The conditions at the rig floor were enhanced

by having clean, non slippery rig floors. Snhvit was developed withdope free premium tubing and casing connections26 which were

laboratory tested related to temperature, corrosion and steel gradesresistance to galling; ref. ISO 13679 CAL IV39. The result showed agalling resistant connection with a higher friction factor which was whythe operator26 was wetting the connections with water prior to stabbingto lower the friction as a contingency in some of the strings. The threadcompounds friction properties affect the value of makeup torque26, 47,


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48,56,but the torque tables that present the recommended torque valuesare not changed by the new applications49.

Tubing and casing installationRunning, handling and installing tubing and casing connections40 arecritical operations related to connection performance. The handling-and makeup equipment should inflict as little mechanical marking as

possible, and the running includes stabbing, makeup, checking themakeup graph and if necessary backing out. There must be goodalignment between the two pipes to prevent cross threading or makeup

problems during stabbing. The makeup torque

41

is critical since itproduces the initial contact pressure53 between the sealing surfaces. Thecontact pressure must be balanced since more contact pressure providesmore sealing but also increases the sensitivity to galling. Theconnections vendors have defined minimum, optimum and maximummakeup torque specified for each type, size, material and connection.The oilfield practice is to perform the makeup torque between optimumand maximum. Over torque occurs when the makeup torque is abovethe maximum makeup torque, and it is performed to increase thecontact pressure and minimize the effects of dynamic loads, but it canalso result in reduced connection integrity. Some operators define over

torque as critical or non-critical over torque depending on shoulderdeformation. Operators on the NCS use different torque values for thesame connection; some operators use torque values from laboratorytests or torque values that other companies do not know exist and thereare examples where operators use double makeup torque level. Anexample illustrating this is casing installation at Snorre P-02 in 200418where the New Vam 9 5/8 47 lbs/ft grade N80 ksi casing stringconnections were exposed to double torque values. The connectionstorque values were 23.6 kNm during installation and exposed to 42kNm during operation due to tight hole (included down weight androtation to reach end target), even though the manufacturer had defined

maximum torque as 21.6 kNm. This example is not typical for theselected company, connections or vendors. The example indicates thatthere may be a non-consistent practice and a high degree of freedomrelated to torque values, and this needs to be further evaluated.


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The torque graph provides valuable information for detecting torquedistributions and potential problems related to the threads, seal andshoulder but they do not guarantee connection seal ability. Qualified

personnel with operational experience and competence related to sealintegrity and connections are therefore needed in addition to themakeup equipment. The industry requires40 a competent person on thedrill floor at all times checking the makeup graphs. If there is anyunacceptable makeup graph, then the string should be pulled back toinvestigate any anomalies. Some challenges have been identified inrelation to the computer controlled makeup equipment with poor

resolution

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where the makeup graph looks acceptable, but the graphmay not be acceptable with increased resolution. Other challenges arerelated to human factors and the person who qualifies the makeuptorque. The vendors should evaluate the use of automatic solutionsrelated to evaluating the torque with alarms or different types of colorswhen the torque is not in accordance with the vendors suggestedmakeup graph. The industry is using an Ultrasonic ReflectionAmplitude Pressure (URAP) 71 technology to qualitatively evaluate thecontact stress distribution on the radial seal surface of a premiumconnection after makeup. This technology can identify geometrical andmanufacturing variations and makeup variations in the manufacturing

facility. The basis in this technology can be useful offshore aftermakeup of tubing and casing connections to verify the integrity of thetubing and casing connections before they are lowered into the well.This technology should be included in the automatic makeup toolsoffshore and activated after each connection makeup to verify integrityand thereby become a contributing factor to improving well integrity intubing and casing connections.

Testing and verifications

Testing of the tubing and casing integrity is performed to verify that theequipment is properly installed and the equipment can withstand the

possible exposed pressure. NORSOK Standard D-0106 defines theinitial test and verifications of the casing and tubing to include leak

testing to maximum anticipated differential pressure and leak testing

during completion activities when the casing and liner has been drilled

through. Pressure testing is acceptable for verification of the tubingand casing string36,and the operational testing is performed from 0 to


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Barriers

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345 BAR to verify the tubing or casing integrity which considers thestring as static loaded. The tubing and casing string are exposed tocyclic conditions and changes over time including variable loads due tochanges in temperature or pressure during well operations109. Thisshould also be included in the test program which means testing thetubing and casing string from 345 to 0 to 345 BAR for some cycles toverify the string integrity; the number of test cycles should be definedaccording to operational experience.

Competence, knowledge and training and capacity

The tubing and casing integrity and performance are dependent on theoperators knowledge, competence, stress limitations, capacity andexperience but also on technical factors related to the equipment, thehuman machine interface and organizational factors influencing the

performance during design, storage, lifting and handling40, running,installation, testing, verification, monitoring, and well operations suchas well killing or well stimulation. These factors include all operatorsincluding rig supervisor, drilling an

Contribution to Well Integrity and Increased Focus on Well Barrieres From Life Cycle Aspect

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