THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

Tekspenuh

(1)al. ay. a. AGEING OIL WELL INTEGRITY ASSESSMENT AND REHABILITATION. U. ni. ve r. si. ty. of. M. RAMESH RAMASAMY. FACULTY OF ENGINEERING UNIVERSITY OF MALAYA KUALA LUMPUR 2018.

(2) ay. a. AGEING OIL WELL INTEGRITY ASSESSMENT AND REHABILITATION. of. M. al. RAMESH RAMASAMY. si. ty. THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY. U. ni. ve r. FACULTY OF ENGINEERING UNIVERSITY OF MALAYA KUALA LUMPUR. 2018.

(3) . UNIVERSITY OF MALAYA ORIGINAL LITERARY WORK DECLARATION. Name of Candidate: Ramesh Ramasamy Matric No: KHA150032 Name of Degree: Doctor of Philosophy (Ph.D) Title of Project Paper/Research Report/Dissertation/Thesis (“this Work”):. a. Ageing Oil Well Integrity Assessment and Rehabilitation. ay. Field of Study: Structural Engineering and Materials (Civil Engineering) I do solemnly and sincerely declare that:. ve r. si. ty. of. M. al. (1) I am the sole author/writer of this Work; (2) This Work is original; (3) Any use of any work in which copyright exists was done by way of fair dealing and for permitted purposes and any excerpt or extract from, or reference to or reproduction of any copyright work has been disclosed expressly and sufficiently and the title of the Work and its authorship have been acknowledged in this Work; (4) I do not have any actual knowledge nor do I ought reasonably to know that the making of this work constitutes an infringement of any copyright work; (5) I hereby assign all and every rights in the copyright to this Work to the University of Malaya (“UM”), who henceforth shall be owner of the copyright in this Work and that any reproduction or use in any form or by any means whatsoever is prohibited without the written consent of UM having been first had and obtained; (6) I am fully aware that if in the course of making this Work I have infringed any copyright whether intentionally or otherwise, I may be subject to legal action or any other action as may be determined by UM. Date:. U. ni. Candidate’s Signature. Subscribed and solemnly declared before, Witness’s Signature. Date:. Name: Designation:. ii.

(4) AGEING OIL WELL INTEGRITY ASSESSMENT AND REHABILITATION ABSTRACT Keywords: well integrity, platform conductor, corrosion Majority of the prominent oilfields around the world are becoming mature, with their wells exceeding 30-40 years, and in some cases, even up to 50 years. The common dilemma faced by the operators worldwide dealing with these ageing fields spanning. a. across the North Sea, Middle East and Southeast Asia are ways to deal with the associated. ay. ageing assets, particularly the well structural barriers. The deteriorations on these. al. structures, consisting of corrosion, cement shortfall, loss of centralization and other structural defects, in addition to the increased operating demands are pushing the. M. structures beyond their allowable limits to handle the excessive loads, hence creating. of. larger risk profile for the operators to deal with. This thesis is primarily aimed to provide substantial contribution to identifying and highlighting some of the key well integrity. ty. challenges, uncertainties and present validated methods to address these issues. This. si. thesis is also a synthesis of work from a broad range of studies pertaining to well integrity,. ve r. encompassing various individual aspects of ageing related degradations, specialized inspections, structural assessments and rehabilitation works. The deterministic global. ni. structural assessments are proposed for the as-built conditions, and relevant corrosion. U. measurements will enable the in-place evaluations to be carried out. This is followed by development of a prioritization criteria for categorizing the more critical wells urgently requiring repairs. This group is further streamlined by more advanced inspections to quantify some of the uncertainties involving the downhole conditions and remaining annular cement bond with the development of a conductor/casing preload inspection tool based on the ultrasonic longitudinal critically refracted wave. The use of probabilistic methods on structural reliability is also proposed using the first-order method and computer-based Monte-Carlo and Bootstrap algorithms to address the uncertainties. iii.

(5) associated with the ageing wells. A coherent decision-making methodology is developed and presented in this thesis to further consolidate the repairs/rehabilitations planning of the selected wells. Finally, the structural repair designs are proposed based on existing concepts involving welding, and more economical techniques involving clamping and grouting to provide load mitigations on the existing well structures for continued extended life. Application of the analyses and monitoring methods proposed in this thesis is applied. a. onto a group of 40-50 years old water injection and production wells from a shallow-. ay. water high-salinity brownfield. Conclusions can be drawn from the structural assessments and monitoring techniques proposed in this thesis, that the successful life extensions of. al. ageing wells are completely feasible and can be systematically carried out very. U. ni. ve r. si. ty. of. M. effectively, and at an optimal cost within the limitations stipulated in this work.. iv.

(6) PENILAIAN DAN PEMULIHAN TAHAP KEUTUHAN TELAGA MINYAK YANG BERUSIA ABSTRAK Kata Kunci: keutuhan telaga, konduktor platform, kakisan Kebanyakan medan minyak di dunia sedang menghampiri tempoh akhir hayat mereka, dan kini berusia di dalam linkungan 30-40 tahun, dan ada yang beroperasi melampaui 50. a. tahun. Salah satu masalah umum yang dihadapi oleh syarikat minyak di sekitar Laut Utara. ay. (UK), Timur Tengah dan Asia Tenggara adalah pengusiaan telaga-telaga minyak. Kerosakan umum akibat pengusiaan merangkumi kekaratan, kehilangan simen di dalam. al. jurang annulus serta kehilangan struktur pemusatan pada paip konduktor telaga minyak. M. tersebut. Ini mengakibatkan tekanan tinggi pada struktur telaga minyak yang melebihi tahap tekanan yang dibenarkan, yang akan seterusnya meninggikan profil risiko kepada. of. syarikat pengoperasi minyak yang mengendalikan medan itu. Tesis ini memberi tumpuan. ty. yang khusus untuk menyumbangkan pengetahuan tambahan kepada ilmu yang sedia ada. si. untuk mengemukakan cabaran yang dihadapai di dalam keutuhan struktur telaga minyak, memberikan gambaran lengkap terhadap ketidakpastian yang wujud dan mencadangkan. ve r. proses penganalisaan yang terperinci untuk menyelesaikan masalah tersebut. Tesis ini juga mengandungi gabungan kerja-kerja penyelidikan dari pelbagai bidang yang releven. ni. kepada telaga minyak yang berusia yang merangkumi degradasi akibat usia, kaedah. U. pemeriksaan khusus, kaedah penilain struktur serta kaedah pemulihan yang efektif. Kaedah penilaian berketentuan terhadap struktur pada peringkat global dicadangkan untuk dilakukan pada struktur seperti yang terbina semasa penggerudian minyak asal, diikuti oleh gabungan dengan hasil pemeriksaan semasa untuk penilaian terkini terhadap struktur terusia yang tersebut. Satu kaedah pengutamaan yang akan membezakan telaga yang kritikal daripada yang masih mampu beroperasi secara selamat dicadangkan mengikut tahap ketebalan dinding paip konduktor dan paip seterusnya, untuk permulaan. v.

(7) kerja-kerja penyelengaraan dan pemulihan. Kumpulan kategori kritikal ini diselaraskan lagi untuk pengoptimuman bilangan telaga menerusi kaedah pemeriksaan khusus yang dihasilkan daripada kajian ini. Pengunaan kaedah penilaian berasaskan statsitik dan kebolehpercayaan struktur juga digabungkan untuk memperolehi gambaran yang lebih tepat, dengan menggunakan kaedah berasaskan algoritma Monte-Carlo dan Bootstrap. Satu kaedah membuat keputusan yang koheren disediakan untuk menggabungkan semua. a. proses analisa, penilaian dan pemeriksaan untuk menyumbang pengetahuan terhadap. ay. rawatan untuk pemanjangan usia untuk telaga-telaga ini. Kaedah penilaian dan pemeriksaan yang diselidiki telah dijalankan terhadap sekumpulan telaga minyak. al. disekitar usia 40-50 tahun yang didapati di kawasan laut cetek dengan kandungan garam. M. tertinggi. Kesimpulan penyelidikan ini mendapati gabungan teknik penilaian berketentuan dan kebolehpastian/statistik serta kaedah pemeriksaan khusus yang. of. dihasilkan dapat menyumbang secara efektif untuk melanjutkan pengoperasian telaga-. U. ni. ve r. si. ty. telaga berusia secara sistematik pada kos yang rendah.. vi.

(8) ACKNOWLEDGEMENTS My highest gratitude and unconditional submission to the Almighty God for being the Source of all that exists, the Cause for all that is, was and ever will be. I would like to sincerely thank Associate Professor Dr. Zainah Ibrahim and Dr. Chai Hwa Kian for their undivided support and constant guidance in enabling me to complete this research.. a. My greatest appreciation to my dearest family; Indira, Rishiges, Simha and Durgaasri. ay. for tolerating and understanding those late nights which I spent working, and for being my inspiration and strength which drives me to be better.. al. I am indebted to my company, Azakti Energy Sdn. Bhd. for providing me with the. M. relevant funding, equipment and field data to carry out this research. I am also thankful to my friends, colleagues and associates with whom I have had. of. countless discussions, brainstorming and debates throughout the course of this study, and. U. ni. ve r. si. ty. whom have provided invaluable ideas and thoughts into this research.. vii.

(9) TABLE OF CONTENTS. Abstract ............................................................................................................................iii Abtrak................................................................................................................................ v Acknowledgements ......................................................................................................... vii Table of Contents ...........................................................................................................viii List of Figures ................................................................................................................xiii. a. List of Tables................................................................................................................... xx. ay. List of Symbols and Abbreviations ............................................................................... xxii. al. List of Appendices ........................................................................................................ xxv. M. CHAPTER 1: INTRODUCTION ................................................................................ 26 Background ............................................................................................................ 26. 1.2. Problem Statement and Research Objectives ........................................................ 32. 1.3. Scope of Work ....................................................................................................... 33. 1.4. Research Significance ............................................................................................ 35. 1.5. Thesis Overview .................................................................................................... 36. ve r. si. ty. of. 1.1. ni. CHAPTER 2: LITERATURE REVIEW .................................................................... 39 Introduction............................................................................................................ 39. U. 2.1 2.2. Concepts and Terminologies in Well Integrity...................................................... 39. 2.3. What Can Go Wrong in Wells? ............................................................................. 43. 2.4. Well Drilling and Construction ............................................................................. 51. 2.5. Oil Well Corrosion and Inspection Methods ......................................................... 56. 2.6. Well Cementing ..................................................................................................... 67. 2.7. Probability, Risk and Reliability Analysis............................................................. 73. 2.8. Repairs and Rehabilitation ..................................................................................... 76. viii.

(10) 2.9. Codes and Standards .............................................................................................. 81. 2.10 Structural Analyses of Well Integrity .................................................................... 83 2.11 Knowledge Gap in Well Integrity Assessment ...................................................... 84. CHAPTER 3: DETERMINISTIC ANALYSIS .......................................................... 87 3.1. Introduction............................................................................................................ 87. 3.2. As-Built Well Configuration ................................................................................. 87 Well Construction Stages ......................................................................... 89. 3.2.2. Well Cementing ........................................................................................ 95. 3.2.3. Operational Condition .............................................................................. 96. 3.2.4. Well Loads ............................................................................................... 97. M. al. ay. a. 3.2.1. Environmental Data ............................................................................................... 99. 3.4. Geotechnical Data ................................................................................................ 100. 3.5. Global Structural Analysis................................................................................... 102. ty. Model Description .................................................................................. 102. 3.5.2. Dynamic Analysis .................................................................................. 104. si. 3.5.1. In-Place Integrity Assessment ............................................................................. 107. ve r. 3.6. of. 3.3. Corrosion Measurements ........................................................................ 107. 3.6.2. Global In-Place Analysis ........................................................................ 111. ni. 3.6.1. Annuli Cement Assessment ................................................................................. 113. U. 3.7. 3.7.1. Overview and Considerations ................................................................ 113. 3.7.2. Casing Buckling ..................................................................................... 113. 3.7.3. Post-Buckling Assessments .................................................................... 118. 3.7.4. Annuli Cement Axial Capacity .............................................................. 122. 3.8. Guideline and Criteria.......................................................................................... 127. 3.9. Chapter Summary ................................................................................................ 128. ix.

(11) CHAPTER 4: PROBABILISITC FRAMEWORK ................................................. 131 4.1. Introduction.......................................................................................................... 131. 4.2. Structural Reliability Analysis (SRA) ................................................................. 131. 4.3. Theoretical Overview .......................................................................................... 133. Monte-Carlo Simulation (MCS) ............................................................. 137. 4.3.3. Limit State Function (LSF) .................................................................... 140. 4.3.4. Qualitative Risk Assessments ................................................................ 143. ay. a. 4.3.2. Probabilistic Framework for Well Integrity Assessment .................................... 144 FORM ..................................................................................................... 145. 4.4.2. MCS........................................................................................................ 151. 4.4.3. Way Forward with Risk Assessment ...................................................... 155. M. al. 4.4.1. Chapter Summary ................................................................................................ 155. of. 4.5. First Order Reliability Method (FORM) ................................................ 133. ty. 4.4. 4.3.1. CHAPTER 5: INSPECTION AND SCREENING .................................................. 157 Introduction.......................................................................................................... 157. 5.2. UT Stress Measurement Concept ........................................................................ 158. ve r. si. 5.1. UT Wave Overview ................................................................................ 158. 5.2.2. Overview of Acoustoelasticity Theory ................................................... 162. ni. 5.2.1. Experimental Procedure....................................................................................... 165. U. 5.3. 5.4. 5.3.1. Test Specimens ....................................................................................... 165. 5.3.2. UT Probe and System ............................................................................. 166. 5.3.3. Test Setup ............................................................................................... 168. 5.3.4. Test Results ............................................................................................ 172. Numerical Validations ......................................................................................... 181 5.4.1. Model Description .................................................................................. 181. 5.4.2. Analysis Results ..................................................................................... 183 x.

(12) 5.5. Results Comparison ............................................................................................. 191. 5.6. Implementation for Offshore Site Measurement ................................................. 193. 5.7. Well Integrity Screening ...................................................................................... 197. 5.7.2. Loads ...................................................................................................... 199. 5.7.3. User Interface ......................................................................................... 201. 5.7.4. Boundary Conditions .............................................................................. 202. 5.7.5. Solution Sequence .................................................................................. 203. ay. a. Discretisations ........................................................................................ 197. Chapter Summary ................................................................................................ 205. al. 5.8. 5.7.1. M. CHAPTER 6: REPAIRS AND REHABILITATIONS............................................ 208 Introduction.......................................................................................................... 208. 6.2. Composite Wrapping ........................................................................................... 208. 6.3. Remedial Grouting............................................................................................... 211. ty. of. 6.1. Post Cement Top-Up Failures ................................................................ 213. 6.3.2. Cement Integrity Check .......................................................................... 217. 6.3.3. Cement Top-Up Effectiveness Review and Recommendations ............. 221. ve r. si. 6.3.1. Sleeves and Clamps ............................................................................................. 222 6.4.1. Bolted Clamp Design ............................................................................. 225. 6.4.2. Welded Sleeve Design ............................................................................ 228. 6.4.3. Grouted Sleeve Body Design ................................................................. 229. U. ni. 6.4. 6.5. Complete Span Replacement ............................................................................... 230. 6.6. Repairs Case Study .............................................................................................. 233. 6.7. Chapter Summary ................................................................................................ 242. CHAPTER 7: CONCLUSION ................................................................................... 244 7.1. Conclusion ........................................................................................................... 244 xi.

(13) 7.2. Recommendations for Future Studies .................................................................. 246. References ..................................................................................................................... 248 List of Publications and Papers Presented .................................................................... 261. U. ni. ve r. si. ty. of. M. al. ay. a. Appendix ....................................................................................................................... 268. xii.

(14) LIST OF FIGURES. Figure 1-1: WHPT on Shallow Water Field ................................................................... 27 Figure 1-2: Wellhead/Tree Arrangement at the Topside ................................................ 27 Figure 1-3: Platform Conductor Pipes ............................................................................ 28 Figure 1-4: Piping and Valves arrangement.................................................................... 28. a. Figure 1-5: Schematic of Well Layout ............................................................................ 29. ay. Figure 1-6: Conductor and Casing Failure ...................................................................... 30 Figure 1-7: Topside Equipment Vertical-Drop onto Deck ............................................. 30. al. Figure 1-8: Piper Alpha (top) and Macondo (bottom) (DHSG, 2011; Duff, 2008) ........ 31. M. Figure 1-9: Thesis Outline and Chapters’ Connectivity ................................................. 38. of. Figure 2-1: Life Cycle of a Well ..................................................................................... 40 Figure 2-2: Illustration of the Bathtub Curve Hazard Function ...................................... 41. ty. Figure 2-3: Subsea Wells with Pipelines for Hydrocarbon Export (Dessus, 2002) ........ 44. si. Figure 2-4: Failure Statistics with Age of Wells (PSA, 2006)........................................ 45. ve r. Figure 2-5: Active Wells in the NCS (PSA, 2006) ......................................................... 45. ni. Figure 2-6: Well Integrity Survey Carried out on 406 Wells (Vignes & Aadnoy, 2010) ......................................................................................................................................... 46. U. Figure 2-7: Post-Failure Deformation of Casing Hanger ................................................ 47 Figure 2-8: Hole in Production Tubing ........................................................................... 48 Figure 2-9: Collapse of Production Casing ..................................................................... 49 Figure 2-10: Loss of Annular Cement ............................................................................ 49 Figure 2-11: Topside Equipment Drop onto Deck .......................................................... 50 Figure 2-12: Flange and Piping Damage ........................................................................ 50 Figure 2-13: The Maersk Intrepid Jack-Up Rig (Maersk Drilling, 2014) ...................... 51 Figure 2-14: Schematics of the Jack-Up Drilling Operation .......................................... 52 xiii.

(15) Figure 2-15: Drilling Smaller Hole Inside the Surface Casing (Left), and Installing of the Subsequent Inner Casing (Right) .................................................................................... 54 Figure 2-16: Example of Sweet Gas Corrosion (Himipex, 2015) ................................... 57 Figure 2-17: Example of Sour Gas Corrosion in Oil Pipe (Larsen, 2015) ...................... 58 Figure 2-18: Example of Hydrogen Embrittlement (Larsen, 2015) ................................ 59 Figure 2-19: Illustration of Erosion Corrosion Evolution (Corrosion Testing Laboratories, 1995) ......................................................................................................... 60. ay. a. Figure 2-20: Formation of Teardrop Pits Due to Erosion Downstream to Flow-Direction (Corrosion Testing Laboratories, 1995) .......................................................................... 60. al. Figure 2-21: Corrosion Inspection on Platform Conductor (Ramasamy, AlJaberi, & AlJunaibi, 2014) .............................................................................................................. 62. M. Figure 2-22: Ultrasonic Pipe Thickness Measurement System (Danatronics, 2011) ..... 63 Figure 2-23: Pulse Echo Technique ................................................................................ 63. of. Figure 2-24: PEC Tool Used in Well Corrosion Inspection (Munns & Crouzen, 2007) 65. ty. Figure 2-25: PEC Technique (Robers & Scottini, 2002) ................................................ 65. si. Figure 2-26: Automated Ring-Probe PEC System (left) (Rudlin, 2006) and Annulus Calliper Design (right) (Munns & Crouzen, 2007) ......................................................... 65. ve r. Figure 2-27: Multi-Arm Caliper Tool (Probe, 2017) ...................................................... 66 Figure 2-28: Typical Cementing Procedure (King, 2006) .............................................. 69. ni. Figure 2-29: Good Cement Displacement ...................................................................... 69. U. Figure 2-30: Poor Cement Displacement ........................................................................ 69 Figure 2-31: Comparison of Cement Logging Method (Hayman, Gai, & Toma, 1991) 71 Figure 2-32: Schematics Showing Contribution of Annular Cement to Post-Failure Behaviour, with (a) & (b) Downhole Casing Damage in Shortfall Zone, and (c) & (d) Alternative Load Path Provided by Cement.................................................................... 72 Figure 2-33: The Energy Model (Kjellen, 2000) ............................................................ 73 Figure 2-34: The Swiss Cheese Model (Reason, 1997) .................................................. 74 Figure 2-35: Stress-Strain Curves for Various Fibres (Daniel & Ishai, 2005)................ 77 xiv.

(16) Figure 2-36: FRP Repairs in Onshore and Offshore Pipes (Karbhari, 2015) ................. 78 Figure 2-37: Bird-caging Failure on FRP Repair on Pipe Under Compression (Yang, Saevik, & Sun, 2015) ...................................................................................................... 79 Figure 2-38: Illustration of a Welded Sleeve Design ...................................................... 79 Figure 2-39: Illustration of a Bolted Clamp Design........................................................ 80 Figure 2-40: Bolted Clamp Numerical Verifications (Kumar, Abdalla, Rosli, & Howells, 2013) ............................................................................................................................... 81. a. Figure 3-1: Well Configuration ....................................................................................... 88. ay. Figure 3-2: Conductor Lateral Guide (Centralised) ........................................................ 89. al. Figure 3-3: Aged Lateral Guide (Un-centralised) ........................................................... 89. M. Figure 3-4: Typical Offshore Well Construction Stages................................................. 91 Figure 3-5: Well Tubular Axial Spring Analogy ............................................................ 92. of. Figure 3-6: Well Load Distribution................................................................................. 99. ty. Figure 3-7: API Wave Theory Guideline ...................................................................... 100. si. Figure 3-8: Soil P-y Stiffness Curve ............................................................................. 101. ve r. Figure 3-9: Illustration of the FE Model for Well Conductor System .......................... 103 Figure 3-10: Conductor Bending Moment Distribution ............................................... 104. ni. Figure 3-11: Conductor Deflection ............................................................................... 105. U. Figure 3-12: Effective Axial Force along Conductor ................................................... 106 Figure 3-13: Total Absolute Stress along Conductor .................................................... 106 Figure 3-14: Conductor Corrosion Measurement ......................................................... 108 Figure 3-15: Remaining WT Distribution on a Selected Conductor............................. 110 Figure 3-16: Minimum and Average WT at SZR ......................................................... 110 Figure 3-17: Corroded Conductor Bending Moment Distribution ............................... 111 Figure 3-18: Corroded Conductor Stress Distribution .................................................. 112. xv.

(17) Figure 3-19: Maximum Bending Moment and Stresses at SZ Region ......................... 112 Figure 3-20: Effects of External and Internal Loads on Conductor .............................. 114 Figure 3-21: Eccentricity on Aged Well Conductor System ........................................ 115 Figure 3-22: Interaction Ratio for Casing Stability....................................................... 117 Figure 3-23: Interaction Ratio for Casing Strength....................................................... 118 Figure 3-24: The Sinusoidal and Helical Buckling Phenomena inside Wellbore ......... 119. a. Figure 3-25: Well Annuli Cement Arrangement .......................................................... 123. ay. Figure 3-26: Axial Resistance Free-Body-Diagram ..................................................... 123. M. al. Figure 3-27: Missing C-annulus Cement and Severely Corroded Conductor/Casing from Field Visual Inspections (Ramasamy, AlJaberi, & AlJunaibi, 2014) and Borescopic Inspections (Husby, 2014) ............................................................................................ 125 Figure 3-28: Guideline Chart for Conductor WT ......................................................... 128. of. Figure 4-1: Joint Probability and Limit State Functions ............................................... 132. ty. Figure 4-2: LSF Showing Safe and Failure Regions .................................................... 134. si. Figure 4-3: Graphical Illustration of Reliability in Standard Normal Space ................ 135. ve r. Figure 4-4: Random Number Generation ..................................................................... 140 Figure 4-5: Illustration of Response Surface ................................................................ 141. ni. Figure 4-6: The Bootstrap Method................................................................................ 143. U. Figure 4-7: Risk Matrix ................................................................................................. 144 Figure 4-8: Residual Plot .............................................................................................. 148 Figure 4-9: FORM Iterations Convergence .................................................................. 150 Figure 4-10: Bootstrapped Minimum WT at SZ ........................................................... 153 Figure 4-11: Bootstrapped MCS Distribution ............................................................... 154 Figure 5-1: Illustration of UT Wave Components ........................................................ 158 Figure 5-2: PMMA Wedge Design for LCR on Steel Specimen .................................. 162. xvi.

(18) Figure 5-3: Wave Propagation and Plane Stress ........................................................... 162 Figure 5-4: Test Specimens and Tools in the Laboratory ............................................. 166 Figure 5-5: Schematics of the UT Probe ....................................................................... 167 Figure 5-6: UT Interface Box and Software ................................................................. 168 Figure 5-7: Axial Compression Test Setup ................................................................... 169 Figure 5-8: UT Probe Mounting at 50mm Spacing on Specimen ................................. 169. a. Figure 5-9: TOF Measurement...................................................................................... 170. ay. Figure 5-10: PE Test ..................................................................................................... 171. al. Figure 5-11: LCR Subsurface Depth Test ..................................................................... 172. M. Figure 5-12: LCR Wave TOF Measurement (SHS150x6) ........................................... 173 Figure 5-13: Recorded Signals During Loading (SHS150x6) ...................................... 174. of. Figure 5-14: Recorded Signals During Loading (SHS200x10) .................................... 175. ty. Figure 5-15: Recorded Signals During Loading (CHS100x1.5)................................... 175. si. Figure 5-16: Recorded Signals During Loading (CHS145x3)...................................... 176. ve r. Figure 5-17: Pulse Echo Test on 12mm Thick Steel Sample........................................ 177 Figure 5-18: Stress-LCR Speed Relationship from Test............................................... 178. ni. Figure 5-19: LCR Wave Penetration Depth Test Setup ................................................ 179. U. Figure 5-20: LCR Penetration Depth Test for 5MHz transducer .................................. 180 Figure 5-21: LCR Penetration Depth Test for 10MHz transducer ................................ 180 Figure 5-22: Outline of the FE Model for the PE Modelling ........................................ 182 Figure 5-23: Numerical Representation of the UT Transducer Signal ......................... 182 Figure 5-24: Outline of FE Model for LCR Analysis ................................................... 183 Figure 5-25: Longitudinal Wave Propagation in PE Model ......................................... 184 Figure 5-26: PE Signal Measurements on Carbon Steel ............................................... 185. xvii.

(19) Figure 5-27: PE Signal Measurements on PMMA ....................................................... 185 Figure 5-28: Mesh Convergence Check ........................................................................ 186 Figure 5-29: Wave Components Analysis .................................................................... 187 Figure 5-30: Stress Wave Contour of LCR Wave Propagation .................................... 188 Figure 5-31: LCR Signal at Receiver Wedge Under Various Stresses ......................... 189 Figure 5-32: Stress-LCR Speed Relationship from Numerical Analysis...................... 190. a. Figure 5-33: LCR Signals from Test Measurement and Numerical Output ................. 192. ay. Figure 5-34: Acoustoelastic Response from Test and Numerical Model ..................... 193. al. Figure 5-35: Portable and Integrated Measurement System ......................................... 195. M. Figure 5-36: Process Flowchart for In-Situ Measurements .......................................... 196 Figure 5-37: Conductor Discretisation .......................................................................... 198. of. Figure 5-38: Metocean Loads Distribution ................................................................... 201. ty. Figure 5-39: Input Interface for the Simplistic Well Screening Tool ........................... 202. si. Figure 5-40: Output from the Simplistic Well Screening Tool..................................... 204. ve r. Figure 5-41: Well Prioritisation Guideline ................................................................... 205 Figure 5-42: Well Integrity Assessment and Life-Extension Process Guideline .......... 207. ni. Figure 6-1: Composite Wrapping on Pipe (Shamsuddoha, Islam, Aravinthan, Manalo, & Lau, 2013) ..................................................................................................................... 209. U. Figure 6-2: Directional Axes Notations ........................................................................ 210 Figure 6-3: Illustration of Remedial Annular Grouting ................................................ 212 Figure 6-4: Post Top-Up Surface Casing Failure Scenario ........................................... 214 Figure 6-5: Post Top-Up Conductor Failure Scenario .................................................. 214 Figure 6-6: FoS at Surface Casing Interface (Surface Casing Supported Well) ........... 216 Figure 6-7: FoS at Conductor Interface (Surface Casing Supported Well) .................. 216 Figure 6-8: FoS at Conductor Interface (Conductor Supported Well) .......................... 217. xviii.

(20) Figure 6-9: Steel-Cement Composite Section in Bending ............................................ 218 Figure 6-10: Illustration of a Welded Sleeve Design .................................................... 222 Figure 6-11: Illustration of a Bolted Clamp Design...................................................... 223 Figure 6-12: Illustration of Hybrid Repair Design ........................................................ 225 Figure 6-13: Conductor Temporary Supports – Lift (left) and Prop (right) ................. 231 Figure 6-14: Diamond Wire Conductor Cutting Tool .................................................. 231. a. Figure 6-15: Conductor Span Replacement Steps ........................................................ 232. ay. Figure 6-16: WI Platform Views................................................................................... 233. al. Figure 6-17: C-Annulus Corrosion and Absence of Cement ........................................ 233. M. Figure 6-18: WI Well Corrosion Data .......................................................................... 234 Figure 6-19: GVI Record .............................................................................................. 235. of. Figure 6-20: Sleeve Repair Design ............................................................................... 236. ty. Figure 6-21: Sleeve Sizing Parameters ......................................................................... 236. si. Figure 6-22: Coffer Dam Construction and Crown-Finger Sleeve Weldment ............. 238. ve r. Figure 6-23: Sleeve Seam Welding............................................................................... 238 Figure 6-24: Retrofitted Conductor Guide and Deck Centralisations ........................... 239. ni. Figure 6-25: Maximum Allowable Uncemented Span in C-Annulus........................... 240. U. Figure 6-26: Helical Coiling Resulting in Topside Settlement ..................................... 240 Figure 6-27: Post-Buckling Bending Stress from Coiling ............................................ 241 Figure 6-28: Resultant Yield Strength Utilisation ........................................................ 241. xix.

(21) LIST OF TABLES. Table 1-1: Summary of Major Well Integrity Incidents (Etetim, 2013) ......................... 31 Table 2-1: Summary of Oil Well Cements Grades ......................................................... 68 Table 2-2: Risk Acceptance Criteria (IEC, 1997) ........................................................... 75 Table 2-3: Summary of Relevant Codes and Standards for Well Integrity .................... 83. a. Table 2-4: Summary of Critical Literature Review Relevant to Well Integrity ............. 86. ay. Table 3-1: Well Tubular Sizes ........................................................................................ 91 Table 3-2: Tubular Materials .......................................................................................... 91. al. Table 3-3: Major Well Construction Stages and Timeframe .......................................... 92. M. Table 3-4: Axial Well Load Calculation ......................................................................... 94. of. Table 3-5: Annuli TOC Range ........................................................................................ 96 Table 3-6: Well Axial Loads ........................................................................................... 98. ty. Table 3-7: Persian Gulf Metocean Conditions .............................................................. 100. si. Table 3-8: Soil P-y Stiffness Data ................................................................................. 101. ve r. Table 3-9: Sample Remaining WT Measurement ......................................................... 109 Table 3-10: Casing Buckling Parameters ...................................................................... 121. ni. Table 3-11: Casing Helical Buckling Responses .......................................................... 121. U. Table 3-12: Post-Buckling Stresses .............................................................................. 122 Table 3-13: Well Annuli Cement Properties ................................................................. 124 Table 3-14: Minimum Required Cemented Length ...................................................... 127 Table 4-1: Sample Mean and Standard Deviation Comparison (MCS) ........................ 140 Table 4-2: Sample Mean and Standard Deviation Comparison (Bootstraped) ............. 143 Table 4-3: Deterministic Results Obtained from FE Analyses for Conductor Samples ....................................................................................................................................... 146 Table 4-4: Limit State Variables ................................................................................... 147 xx.

(22) Table 4-5: Statistical Properties of Variables................................................................ 147 Table 4-6: Regression Coefficients ............................................................................... 148 Table 4-7: Results for Bootstrapped MCS .................................................................... 154 Table 5-1: Elastic and Acoustic Parameters for Carbon Steel ...................................... 160 Table 5-2: Elastic and Acoustic Parameters for PMMA ............................................... 161 Table 5-3: Test Specimens ............................................................................................ 165. a. Table 5-4: LCR Test Results ......................................................................................... 177. ay. Table 5-5: Acoustoelastic Constant (K) for Carbon Steel ............................................ 178. al. Table 5-6: Acoustoelastic Constant (K) for Carbon Steel ............................................ 180. M. Table 5-7: LCR Analysis Results .................................................................................. 190 Table 5-8: Longitudinal Wave Speeds Comparison ..................................................... 191. of. Table 5-9: LCR Penetration Depth (5MHz Transducer)............................................... 191. ty. Table 5-10: Acoustoelastic Constant ............................................................................ 191. si. Table 6-1: Composite Materials Parameters ................................................................. 210. ve r. Table 6-2: Cement Integrity Check for C-Annuli Top-Up ........................................... 220 Table 6-3: Cement Integrity Check for B and C-Annuli Top-Up ................................. 221. ni. Table 6-4: Clamp Design Parameters ........................................................................... 226. U. Table 6-5: Clamp Stress Calculations ........................................................................... 227 Table 6-6: Post-Clamping Conductor Integrity Check ................................................. 228 Table 6-7: Welded Sleeve Design Parameter................................................................ 228 Table 6-8: Welded Sleeve Stress Calculations.............................................................. 229 Table 6-9: Grouted Sleeve Body Design Parameters .................................................... 230. xxi.

(23) LIST OF SYMBOLS AND ABBREVIATIONS. Analysis of variance. API. :. American Petroleum Institute. ASTM. :. American Society of Testing and Materials. BOP. :. Blowout preventer. CAPEX. :. Capital expenditure. CBL. :. Cement bond log. CHS. :. Circular hollow section. COV. :. Coefficient of variation. DAF. :. Dynamic amplification factor. EOFL. :. End of field life. FE. :. Finite element. FORM. :. First order reliability method. GDP. :. Gross domestic product. HP. :. High pressure. HPHT. :. si. ty. of. M. al. ay. a. ANOVA :. ve r. High pressure high temperature. :. Internal diameter. IR. :. Interaction ratio. LCR. :. Longitudinal critically refracted. U. ni. ID. LP. :. Low pressure. LSF. :. Limit state function. LSV. :. Limit state variables. MCS. :. Monte Carlo simulations. MSL. :. Mean sea level. NACE. :. Nationals Association of Corrosion Engineers. xxii.

(24) :. Norwegian continental shelf. NDT. :. Non-destructive technique. NDT&E. :. Non-destructive technique and evaluations. OD. :. Outer diameter. OPC. :. Offshore Portland cement. OPEX. :. Operating expenditure. PBR. :. Polished bore receptacle. PE. :. Pulse echo. PEC. :. Pulse eddy current. PIP. :. Pipe-in-pipe. PMMA. :. Poly methyl methacrylate. RP. :. Return period. SHS. :. Square hollow section. SIL. :. Safety integrity level. SMUTS. :. Specified minimum ultimate tensile strength. SMYS. :. SOEC. :. SRA. :. Structural reliability analysis. SRB. :. Sulphate reducing bacteria. SSCC. :. Sulphide stress corrosion cracking. SZR. :. Splash zone region. TOC. :. Top of cement. TOEC. :. Third order elastic constant. TOF. :. Time of flight. TT. :. Through-and-through. TVD. :. True vertical depth. si. ty. of. M. al. ay. a. NCS. Specified minimum yield strength. U. ni. ve r. Second order elastic constant. xxiii.

(25) :. Unity check, or stress utilisation. UKCS. :. United Kingdom continental shelf. UT. :. Ultrasonic. VB. :. Visual basic. VDL. :. Variable density log. WD. :. Water depth. WHPT. :. Wellhead platform tower. WIT. :. Well integrity testing. WRF. :. Well risk factors. WSD. :. Working stress design. WT. :. Wall thickness. U. ni. ve r. si. ty. of. M. al. ay. a. UC. xxiv.

(26) LIST OF APPENDICES Appendix A: ABAQUS Input File for Dynamic Analysis of Well Conductors…. 269. Appendix B: Baur and Stahl Casing Stability Procedures……………………….. 280. Appendix C: First Order Reliability Method Iterations………………………….. 286. Appendix D: Well Inspection Record……………………………………………. 290. Appendix E: ABAQUS Input File for Ultrasonic Analyses……………………... 292 298. U. ni. ve r. si. ty. of. M. al. ay. a. Appendix F: VB Scripting for well Screening Tool……………………………. xxv.

(27) CHAPTER 1: INTRODUCTION 1.1. Background. Most of the prominent oil wells in the world are exceeding their calculated design life of 25 years. There are over 100 major oil fields in the world today, and majority of them are over 40 years old, and contribute to over 20% of the world’s daily oil supply (Simmons, 2011). Most of these older fields are located around the world in the North. a. Sea, Middle East, Gulf of Mexico and more recent ones in South East Asia. With the. ay. current slump in oil price, operators worldwide are resorting to focusing on maintaining the continued productions from their older assets, as compared to exploring for new fields.. al. The operational expenditure (OPEX) of running an existing well will be effortlessly. M. justified as compared to the higher capital expenditure (CAPEX) involved in exploration and drilling of new wells. Although most older wells are drilled onshore, the focus of the. of. well integrity is somewhat more emphasised on the unmanned offshore wells due to the. ty. criticality and also infrequent accessibility, as compared to the onshore wells. The higher. si. hydrocarbon content capacity of these offshore reservoir also presents greater demand from the operators to keep these wells operational beyond their design life. Most of these. ve r. ageing oil fields are located within shallow-to-intermediate water depths, and the wellhead platform towers (WHPT) are the predominant construction methods for the. ni. hydrocarbon extraction, as shown in Figure 1-1. These WHPT’s will support the wellhead. U. and surface tree at the topside (shown in Figure 1-2) on the lower deck and the conductors (shown in Figure 1-3), and will also house the piping arrangements which will be used to transport the hydrocarbon to a nearby facility (shown in Figure 1-4). The conductor acts as a pile for the well, and protects the surface casing, inner casing and production tubing, all arranged concentrically and held in place by the annular cement, schematically presented in Figure 1-5.. 26.

(28) a. Wellhead & Tree. of. M. al. ay. Platform Conductors. U. ni. ve r. si. ty. Figure 1-1: WHPT on Shallow Water Field. Figure 1-2: Wellhead/Tree Arrangement at the Topside. 27.

(29) a ay al. U. ni. ve r. si. ty. of. M. Figure 1-3: Platform Conductor Pipes. Figure 1-4: Piping and Valves arrangement. 28.

(30) a ay al M of ty si ve r. Figure 1-5: Schematic of Well Layout. The typical stages involved in the drilling of an offshore well with surface. ni. wellhead/tree are presented in Section 2.4. Usually, wells operating for more than 10-15. U. years will start showing signs of ageing and degradation. This can be observed at several levels. Firstly, the corrosion on the conductor outer walls and formation of pits at the splash zone region (SZR) defined at about ±2m from the mean sea level (MSL). As the corrosion progresses, and lack (or complete absence) of maintenance programme put into place by the operator can result in catastrophic failure of the conductor and casing (Figure 1-6), which will lead to the wellhead and tree dropping down onto the platform deck, damaging the adjoining flanges and piping (Figure 1-7).. 29.

(31) ve r. si. ty. of. M. al. ay. a. Figure 1-6: Conductor and Casing Failure. ni. Figure 1-7: Topside Equipment Vertical-Drop onto Deck. U. The eventual catastrophic incidents which follow these events are much more severe.. A compilation of some of the well integrity incidents are presented in Table 1-1 (Etetim, 2013), and the aftermath of some of the incidents shown in Figure 1-8.. 30.

(32) Table 1-1: Summary of Major Well Integrity Incidents (Etetim, 2013). 2004 2010. Chevron oil fire. None. North Sea (NCS). None. North Sea (NCS) Gulf of Mexico (US). None. Niger Delta (Nigeria). Gas leak through damaged casing Cement not properly set when pressure test was carried out Failed blowout preventer. 11. 2. U. ni. ve r. si. ty. of. M. 2012. Sega Petroleum underground blowout Statoil’s incident on Snorre-A BP’s Macondo blowout. North Sea (NCS). Cause A series of organisational errors and lack of equipment safety requirements. Downhole safety valve (DHSV) not locked-in during workover operation. Casing burst inside the well. a. 1989. Region Fatalities North Sea (UK) 167. ay. 1977. Incident Occidental Petroleum’s Pipe Alpha Incident Ekofisk Bravo blowout. al. Year 1976. Figure 1-8: Piper Alpha (top) and Macondo (bottom) (DHSG, 2011; Duff, 2008) 31.

(33) The common integrity monitoring strategy put in place by operators worldwide are corrosion monitoring and measurements by means of ultrasonic thickness gauge. This will provide the remaining wall thickness on the measured pipe face, such as the conductor and where accessible, the surface casing too. These collected data are oftentimes not critically reviewed and therefore no further action is taken, hence resulting in the failures of the well as presented earlier. Although these are unmanned platforms, risk. a. to humans are minimum, but there are instances when human presence will be there. ay. during inspections and routine workovers, but the major risk effect will be the. M. detrimental and must be avoided at all cost.. al. hydrocarbon exposure to the environment, i.e. oil spills or leakage into the sea which is. 1.2. Problem Statement and Research Objectives. of. The overall lack of knowledge and combination of vigorous inspection-evaluation techniques are prohibiting successful execution of well integrity management policies in. ty. many cases, which have led to the research objectives embodied into this thesis. In view. si. of the background information presented in the preceding section, and the probable. ve r. occurrence of failure which can affect human and the environment, this research is undertaken to investigate further on ageing wells, the main contributing factors, and. ni. rationalising these factors in terms of their significance and provide a validated. U. engineering assessment and inspection plans and methodologies to contribute to the overall knowledge in addressing brownfield life extension issue.. The primary objectives of this research are highlighted as follows, in the order of precedence:. i.. To develop and carry out rapid screening procedure for ageing wells by means of deterministic and probabilistic structural assessments to evaluate available structural resistance and strength factors for continued operations; 32.

(34) ii.. To propose, rationalise and streamline the selection criteria for the critical wells for repairs, and to develop an effective prioritisation methodology based on generic inspections and development of specialised ultrasonic-based nondestructive tool;. iii.. To investigate and rationalise various designs for repairs and rehabilitations for the critical wells which require immediate attention to enable continued. a. operation, highlighting their feasibility at various levels, and subsequently to. ay. propose a consolidated well integrity evaluation procedure to confirm adequate. Scope of Work. M. 1.3. al. margins for continued operations;. To achieve the objectives listed in the preceding section, this research is divided into. ty. illustrated in Figure 1-9 .. of. three phases, and will eventually be implemented into the organisation of this thesis,. si. The first phase is to carry out an extensive literature review in various works on well. ve r. integrity, from all aspects such as well integrity philosophy and strategies currently in place within operator organisations, metal corrosions, cement integrity, ageing-related deteriorations of the wellbore, inspection technologies and their limitations, and. ni. identifying all the uncertainties which inherently contributes towards costly over-. U. conservatisms. Most available work in this field focuses on either individual contributing factors to the deterioration of wells such as excessive corrosions, loss of annuli cement or pressure-temperature effects which lead to leakages in the well barriers. The outcome of this first phase will provide a synthesis of all of these information, in an effort to provide a holistic understanding and awareness into the problem of well integrity management. A simplistic trend will also be drawn from the reviewed data to provide a qualitative. 33.

(35) predictive life-cycle of the well integrity problem, and the future well integrity problems can be identified much earlier.. The first-half of the second phase is to undertake a series of rigorous deterministic structural assessments, carried out by means of analytical and numerical means to evaluate as-built versus the in-place conditions of the wells. Starting from the well loadout during drilling stage form when it was first constructed, up to the current deteriorated. a. state of the well will be assessed by global modelling of the structural components. The. ay. effects of the operational loads and environmental conditions will be considered in this. al. model to evaluate the remaining structural reserve factors or available structural. M. resistance within some degree of conservatism. This is followed by the probabilistic based structural reliability assessments (SRA) to identify the failure probabilities by accounting. of. for the uncertainties in the well information. The first order reliability method (FORM) and the computer-intensive Monte-Carlo Simulations (MCS) and Bootstraping (or. ty. resampling) techniques will be used to quantify the uncertainties within some level of. si. confidence, and to eventually facilitate the evaluations of risks associated with carrying. ve r. out rehabilitations on these wells instead of plugging and abandoning. The development of a set of selection criteria will be proposed to provide an allowable limit for these. ni. assessments. These criteria will be based on straightforward parameter which can be. U. measured directly on the well and will be presented in the form of a prioritisation curve. The ageing wells being assessed will be populated in the curve and the levels of their criticality will be acknowledged and ranked for repair works.. The second-half of this phase involves the development of an ultrasonic-based nondestructive inspection tool utilising the longitudinal critically refracted (LCR) wave propagation to detect the collective in-place condition of the annuli cement, soil bearing factors and overall load carrying percentages of the conductor-casing-tubing. 34.

(36) arrangement. The measured preloads on the well structures will increase the structural resistance of the wells being assessed, since this will significantly reduce the uncertainties of the annuli cement conditions and conductor-casing interconnectivity. This streamlining of the wells’ criticality will be a potential cost-saving effort for the operators, especially those currently operating hundreds of aged wells within their matured brownfields. This novel tool, although utilising an established theory, is new to the offshore industry.. a. Finally, the third phase will consolidate these findings and investigate the effectiveness. ay. of various repair techniques, and advantages/disadvantages will be elaborated supported. al. by the design evaluations. The feasibility of these repairs will be critically evaluated and presented from an extended service life perspective. The repairs will also address all. M. deteriorations currently existing on the well’s structural barriers and to inhibit further. of. deteriorations such as corrosion in the extended operating lifespan. The post-repair assessments are presented to provide a critical consideration towards failure mitigation. ty. after the rehabilitation phase of the aged wells, and the possibly reduced severity level of. ve r. si. such failure.. 1.4. Research Significance. Currently, there are large numbers of matured brownfields in operation which are. ni. producing a significant percentage of world’s crude oil supply. These fields are mainly. U. located on shallow water depths, and were drilled some 30 to 40 years ago with the limited technologies which existed at that time. Today, these assets consisting primarily of WHPT’s are in a degraded state and in some case, have failed catastrophically. In the current market of volatile and uncertain oil price, it is apparent that the continued operation of existing asset is very cost-effective as compared to drilling for new fields, which are driving the exploration teams farther into the deeper waters with enormous costs and risks. Due to the lack of awareness and knowledge in handling of ageing well. 35.

(37) integrity issues, operators are commonly resorting to superficial repairs on critical wells without any understanding of the contributing factors, and effective inspections and inplace structural assessments. In most cases, wells are repairs either prematurely, or worse, fitted with an ineffective rehabilitation scheme which will not deter the imminent failure. The thorough and in-depth understanding of each contributing factors and their severity, combined with the specialised inspections and evaluations will help tackle this problem. a. efficiently and safely. This will greatly contribute towards the sustainability of the. ay. offshore oil industry in the coming decades and to optimise overall costs of oil productions after certain number of years. It is therefore the prime objective of this thesis. al. to address the aged well integrity subject, pertaining to structural barriers, with the. Providing a comprehensive and holistic approach towards addressing the. of. i.. M. following novelties:. assessment of aged well integrity, considering the conductor, casings and. ty. annuli cement by development of a systematic and validated evaluation. Developing and implementing an ultrasonic field device to help streamline the. ve r. ii.. si. procedure;. over-conservatisms involved in the design codes to cater for late life integrity. iii.. Providing a thorough and in-depth awareness to operators by consolidating the. U. ni. evaluations to optimise cost of rehabilitations;. findings throughout this thesis, which will help reduce incidents associated with aged well operations.. 1.5. Thesis Overview. The graphical outline of the arrangement of this thesis and the chapters’ inter-relation is presented in Figure 1-9. Chapter 2 provides a survey and review of the various literatures in the areas of offshore oil well and structural integrity including the synthesis. 36.

(38) of these ideas into a consolidated and systematic process for solving the associated challenges and the various uncertainties therein. Chapters 3 and 4 provide the detailed global and local analyses carried out on the deterministic and probabilistic solutions to obtain the remaining structural resistance and failure probabilities based on available inspection data and original drilling records. The categorisation of the wells based on these assessments for repairs and their prioritisations on criticality will be presented in. a. the form of measurable allowable criteria, whilst the key parameters in the oil well. ay. construction will be identified as being governing in the integrity management of ageing wells. Chapter 5 presents the implementation of the established ultrasonic inspection. al. methods to develop an in-situ monitoring tool to further assist in the streamlining of the. M. wells which are categorised for repairs. This is deemed to further reduce any conservatisms and beneficial for vast cost reductions associated with offshore repair. of. works. Chapter 6 will investigate the various repair methods for ageing wells to continue. ty. operations and to ensure a successful life extension strategy within feasible execution. si. capacity for operators. Chapter 7 will conclude the findings in this thesis and attempt to provide an effective guideline for operators in identifying critical ageing oil wells and to. ve r. implement life extension strategies for continued production, and mainly to avoid any. U. ni. undesired catastrophic incidents.. 37.

(39) Chapter 1: Introduction. Chapter 2: Literature Review Review of available knowledge, and existing methods and technology in this area. Chapter 4: Probabilistic Framework. Structural assessments based on nonlinear finite element method of wells exposed to construction, operational and environmental conditions, and incorporation of inspection data for integrity screening decisions.. Structural reliability analysis and quantification of risks, and decision methods based on probabilistic evaluations of uncertainties based on available data, forming a framework for risk evaluations.. al. ay. a. Chapter 3: Deterministic Assessments. of. M. Chapter 5: Inspection and Screening Development of specialised inspection tool for streamlining the decision making for well-structures rehabilitation based on ultrasonic longitudinal critically refracted wave propagation.. Chapter 7: Conclusions. ve r. si. ty. Chapter 6: Repairs and Rehabilitations Methods of repairs of well structural barriers and critical considerations.. U. ni. Figure 1-9: Thesis Outline and Chapters’ Connectivity. 38.

(40) CHAPTER 2: LITERATURE REVIEW 2.1. Introduction. This chapter will focus on the review of various published literatures in the field of well integrity, based on the various contributing factors which affect the overall agedependant degradation on the oil well. The existing knowledge will provide a solid foundation to further progress in understanding, evaluating and life extension of ageing. a. wells. Starting with the relevant definitions, this chapter will introduce the individual. ay. contributing factors of deterioration from corrosion, cement loss, structural damage, operational demand, environmental condition and the overall lack of awareness and. al. understanding in addressing the well integrity issue to propose for rehabilitation to. M. continue operations, or to plug, abandon and decommission the well depending on the. 2.2. of. feasibility.. Concepts and Terminologies in Well Integrity. ty. The life cycle of a well can be illustrated as shown in Figure 2-1. The design of the. si. well consist of the geological assessment, identifying the well objectives and the. ve r. engineering aspects of the wells. The construction of the well involves drilling, installation of conductor-casings-tubing and cementing of their annuli. The testing and. ni. evaluation of the well as part of the appraisal stage is also carried out and the well. U. stimulations (if needed) will be planned and executed accordingly. The operations stage of the well will see the flow of hydrocarbon and monitoring of the flow pressure to ensure adequate sealing and overall integrity of the well is maintained. The checks for leaks and production volumes will be metered and monitored. Other regular inspections also will be carried out at various levels, as determined by the operating company in place policy. The life extension stage will commence once the well approaches the design life, as illustrated by the bathtub curves hazard function in Figure 2-2, which has been developed to assist the product development industry (Lienig & Bruemmer, 2017). The initial stage. 39.

(41) reducing failure rate is due to design flaws or inadequacies of the system, followed by the steady state in-service random failures, with the final wear-out failure or end of field life (EOFL). Prior to this stage, servicing and repairs of the well can be carried out to provide corrective measures to ensure overall integrity in an extended operating life. In the scope of the oil wells, the repairs and/or replacements of components including wellhead, downhole components, conductor and casing, and topping-up of annuli cement will be. a. carried out as required. The life extension objective is usually a short to mid-term goal,. ay. until either the cessation of production of the well or alternative new platforms/tieback installation are anticipated. In the event of cessation of production, the well will be. al. plugged and the decommissioning activities will take place to remove the well from the. M. field.. of. Construct. Operate/Maintain. ty. Design. U. ni. ve r. si. Life Extension. Cessation/Suspension. Decommissioning Figure 2-1: Life Cycle of a Well. 40.

(42) Failure Rate. Design Life. Extended Life Acceptable Limit. Time. a. Figure 2-2: Illustration of the Bathtub Curve Hazard Function. ay. Well integrity can be generally defined as the application of technical, operational and organisational solutions to reduce risk of uncontrolled release of formation fluids. al. throughout the life cycle of a well (NORSOK, 2013). The NORSOK-D-010 is purely a. M. functional code which leaves the specific solutions to the operating companies when. of. carrying out any well integrity engineering activities. However, the minimum requirements on the equipment and types of solutions are set within the code to allow the. ty. operators to meet these requirements by any of the proposed solutions/equipment. This. si. definition indirectly puts the emphasis on the relevant drilling and completions personnel. ve r. to identify the solutions which will result in a safe well life cycle whilst adhering to the minimum requirements of the code. The definition of wells in the oil and gas industry are. ni. accepted as being the physical assets which connects the reservoir to the surface, and. U. produces oil, water, gas, reservoir fluids and contaminants (Cameron, 2010). The definition for life extension is accepted as the process of extending the operational life of a structure beyond the life considered during the structure’s design (API, 2014). This includes overall rehabilitation and structural rejuvenation by means of permanent or temporary repairs, props and other means necessary to mitigate the loads within the structural barriers through alternative paths, bypassing weaker section of the barriers, and keeping the overall well barriers intact. Other related terminologies which accompany the study of well integrity are defined as follows (Oil & Gas UK, 2012):. 41.

(43) i.. Asset: any offshore structures, plants and equipment which connects wells, pipelines and other safety-critical equipment;. ii.. Ageing: any aspects of deteriorations which adversely affects the ability of the asset to perform the designed function, and includes organisation, manpower, standards and obsolescence;. iii.. Design Life: the calculated duration of the asset’s life during which it can. Service Life: anticipated life of the asset where it actually performs the. ay. iv.. a. perform the designed functions effectively;. designed operations;. Deterioration: detrimental changes to the asset from its original designed. al. v.. M. conditions, which adversely affects its ability to perform the designed functions, and consists of fatigue, wear, effects of changes to operational and. of. environmental requirements, or naturally occurring effects due to operations.. ty. Based on these definitions, as the link between the source of energy in the sub-surface. si. reservoir and the surface, wells must be designed and constructed to provide sufficient. ve r. barriers to contain and control the flow of hydrocarbon from the reservoir. The wells are designed with the calculated operational life of usually 25 to 30 years, which commences. ni. from the first drilling phase. Beyond the design life, the well may be subjected to. U. operational requirements such as completions, injections and stimulations, interventions and workover, maintenance and eventually plug and abandonment. A comprehensive well integrity management strategy need to consider all these phases in a well life cycle, in addition to the conventional production operations which it is intended for, and provide a reliable in-place state of the well at any point of its life cycle.. The overall well integrity philosophy covers a broader sense which dictates the reliable production assurance at any point of the well’s operational life. This assurance also. 42.

(44) prescribes that the environment and human factors linked within the vicinity of the well be free from any form of harm and losses . This assurance is also required to be delivered within the requirements stipulated by the statutory regulations, recommended practices and engineering standards (Devold, 2015). The importance of identifying the continuous improvements in the delivery of the well integrity assurance also demands a thorough understanding of the operating environment and the enabling technologies to guarantee a. a. successful well engineering. In this thesis, a subset of this broader scope of well integrity,. ay. focusing mainly on the structural barriers, will be explored. Nevertheless, by having the adequate barriers in place and functional within the required limits, will result in the. al. reliable production assurance, as stated in the broader sense of well integrity. This must. M. be accompanied with the awareness among personnel, a thorough reporting culture and technical team with relevant competency to handle the task, forming the recipe for. of. efficiently undertaking the well integrity activities (Nolan, 2012).. What Can Go Wrong in Wells?. ty. 2.3. si. Over the past 30 years, significant technological advances have been made in the area. ve r. of well drilling industry. The earlier offshore wells were usually drilled for 3km reservoir reach form the platform, and several platforms were required if farther reach is required.. ni. These recent years, the reach has been extended to a remarkable 12km deep reservoirs.. U. This is made possible through developments in subsea technologies and installations. Figure 2-3 shows a typical setup for subsea wells in deeper waters, where pipelines (and risers) are used to export out the hydrocarbon from the reservoir to the nearby platform or processing facility (Dessus, 2002).. 43.

(45) a. ay. Figure 2-3: Subsea Wells with Pipelines for Hydrocarbon Export (Dessus, 2002). al. A single platform can now replace several older platforms. The advancement in. M. drilling methods such as multiple reservoir contact (MRC) can also be credited for replacing the need for several platforms to cover a wider field area with a single platform. of. with an extended horizontal reach. Although this can be seen to reduce the operational risk to a single well instead of risks associated with several wells, but the greater risk. ty. exists due to the extended reach ability of these wells, with the requirement of the. si. structural barriers to be intact along the depth, providing zonal isolations for the wells. ve r. (Torbergsen, 2012).. ni. In the Norwegian Continental Shelf (NCS), a survey carried out by the Petroleum. Safety Authority (PSA) in 2006 concluded that majority of the failures are in ageing wells. U. in the offshore fields are damages in the barrier elements, i.e. the tubing, followed by the casing and annuli cement (PSA, 2006), as shown in Figure 2-4. The surveyed wells also comprise primarily of the platform wells, as shown in Figure 2-5, whereas the more recent developments in the deeper waters see more subsea installation and subsea wells (i.e. wellheads located in near the seabed, with conductor stickup of about 1 to 2m above seabed). A similar survey carried out in the NCS on 406 operational wells across 12 fields also exhibits signs of barrier failures, which amounts to about 18%, where the tubing,. 44.

(46) casing/conductor and cement contributes to over 50% of integrity issues, as shown in. of. M. al. ay. a. Figure 2-6 (Vignes & Aadnoy, 2010).. U. ni. ve r. si. ty. Figure 2-4: Failure Statistics with Age of Wells (PSA, 2006). Figure 2-5: Active Wells in the NCS (PSA, 2006). 45.

(47) a ay al. M. Figure 2-6: Well Integrity Survey Carried out on 406 Wells (Vignes & Aadnoy, 2010). of. A compilation of worldwide well integrity statistical data, from a comprehensive. ty. search (AlAwad & Mohammad, 2016) categorised wells according to their age and the. si. occurrence frequency of each integrity issue which are reported. This study shows that. ve r. offshore wells over 30 years old suffer from deteriorations of the tubing, casing and cement, apart from other barriers such as valves and wellhead more frequently as compared to any other issue. In fact, the casing and cement issues start to creep on to. ni. wells with just over 15 years of service. Studies carried out in the Middle East region also. U. follows a similar trend to those in the North Sea, with structural barriers and cement playing significant roles in well integrity issues (Ramasamy, AlJaberi, & AlJunaibi, 2014; Vignes, 2011).. It is now evident that barrier failures significantly dominate the well integrity issue surrounding ageing wells over 15 years old. A failure of any of the well barrier will automatically reduce the overall integrity of the well thus failing to comply with any of the requirements defined earlier. In an event of failed well barrier, the next course of 46.