Deepwater Well Design and Construction

API RECOMMENDED PRACTICE 96 FIRST EDITION, MARCH 2013

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Foreword

Life cycle well integrity is an important objective in the design and execution of a deepwater (DW) well program. Technical, operational, and organizational solutions are to be employed such that the risk of an unintended release of formation fluids is minimized during drilling, completion, operational, and abandonment phases of the well. This document describes established well design practices and operational procedures that engineers, well planners, and operators consider when planning and executing a DW well project. It is not intended to prohibit the development and application of new technology.

The verbal forms used to express the provisions in this recommended practice are as follows:

• the term “shall” denotes a minimum requirement in order to conform to the recommended practice;

  
  

• the term “should” denotes a recommendation or that which is advised but not required in order to conform to the recommended practice;

  
  

• the term “may” is used to express permission or a provision that is optional;

  
  

• the term “can” is used to express possibility or capability.

  
  

  Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

  
  

  This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, NW, Washington, DC 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

  
  

  Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 1220 L Street, NW, Washington, DC 20005.

  
  

  Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, DC 20005, standards@api.org.

  
  

  iii

  
  

  1. Scope 1

  2. Normative References 2

  3. Terms, Definitions, and Abbreviations 2

     1. Terms and Definitions 2

     2. Abbreviations 10

  4. Deepwater Rig Systems and Subsea Configurations 11

     1. General 11

     2. Rig Options 12

     3. Stationkeeping System 12

     4. Marine Drilling Riser System 14

     5. BOP System 14

     6. BOP Control System 16

     7. Emergency Functions 18

     8. Subsea Wellhead and Production Tree Configurations 20

     9. Remotely Operated Vehicle Systems 20

  5. Well Design Considerations 21

     1. General 21

     2. Deepwater Well Architecture 21

     3. Barrier Philosophy 29

     4. Load Cases Drilling and Completion Conditions 37

     5. Tubing Design 41

  6. Special Considerations for Drilling 43

     1. Wellheads 43

     2. Casing Hanger/Seal Assembly Lockdown to Subsea Wellhead Systems 46

     3. Structural Casing 49

     4. Riserless Mudline Hangers and Submudline Hangers 50

     5. Cemented Shoe Track System 51

     6. Subsidence/Compaction 52

     7. Salt Loading 52

     8. Pore Pressure Prediction 54

     9. Shallow Hazards Considerations 56

     10. Gas Hydrate Formation 58

     11. Liner Hangers 58

     12. Expandable Tubular Goods 60

     13. Alloys in a Cracking or Corrosive Environment 61

     14. Downhole Threaded Connections 61

     15. Casing Landing Strings 62

     16. Tension Leg Platforms/Spar Considerations 63

     17. Annular Pressure Build-up Considerations 64

     18. Annular Abandonment Considerations 67

         
         

         v

         
         

  7. Special Considerations for Completions 67

     1. Completion Fluids 67

     2. Materials 68

     3. Tubing/Work String Connections 69

     4. Flow Assurance 70

     5. Wellbore Considerations 71

     6. Deepwater Sandface Completion Techniques 73

     7. Intelligent Wells 74

     8. Fishability of Tubing and Work String Components 74

     9. Injector Well Considerations 75

  8. Drilling Operations Considerations 75

     1. Riserless Operations 75

     2. Operations with Subsea BOP and Riser Installed 76

  9. Completion Operations Considerations 86

     1. Completion Operation Phases 86

     2. Well Testing and Unloading Considerations 90

     3. Preproduction Start-up Review 96

  10. Management of Change 97

      1. Unexpected Events 97

      2. Well Contingency Plans 98

      3. Stakeholder Interface 98

      4. Stop Work Authority 98

  Annex A (informative) Examples of Barriers Employed During Operations 100

  Annex B (informative) Example Barrier Definitions 124

  Annex C (informative) Examples of Inflow Testing 149

  Bibliography 156

  Figures

  1. Marine Drilling Riser System Example 15

  2. BOP Controls 18

  3. Well Architecture Examples 23

  4. Normal-clearance Deepwater Casing Schematic with 30-in. Structural Casing 24

  5. Tight-clearance/Long-string Intermediate Casing Schematic with 36-in. Structural Casing 25

  6. Representation of Barrier Verification Categories 33

  7. Example of Hydrate Stability Envelope 57

  8. Subsea Tree with Tubing Head and “A,” “B,” and “C” Annuli 66

  9. Subsea Test Tree 93

  10. Surface Flow Head 94

  11. Coil Tubing and Lift Frame 95

  1. Drilling Ahead 101

  2. Emergency Evacuation/Disconnect/LMRP Repair 106

  3. Abandonment After Drilling out the Shoe Track (Full BOP Removal) 110

     
     

  4. Abandonment without Drilling the Shoe track (Full BOP Removal) 111

  5. Tripping After Tubing-conveyed Perforating 115

  6. Flowback Through Production Tubing to Rig 120

  
  

  Tables

  1. Typical Rig and System Options 12

  2. Typical Casing Types and Description 27

  3. Example Basis of MASP Internal Load Cases 39

  4. Tubing/Workstring Design Requirements 43

  5. Completion Tubing String Loads 44

  6. Completion Work String Loads 45

  7. Salt Properties 53

  8. Unloading the Well to the Rig during Completions 91

  1. Drilling Ahead 102

  2. Emergency Evacuation/Disconnect/LMRP Repair 107

  3. Abandonment (Full BOP Removal) 112

  4. Tripping After Tubing-conveyed Perforating 116

  5. Flowback Through Production Tubing to Rig 121

  1. Hydrostatic Fluid 125

  2. Casing 127

  3. Cement Behind Casing or Liner 129

  4. Cemented Shoe Track 132

  5. Cement Plugs 135

  6. Subsea Wellhead 137

  7. Subsea Blowout Prevention Equipment 138

  8. Subsea Production Tree 140

  9. Production Tubing String 141

  10. Production Packer 143

  11. Surface-Controlled Subsurface Safety Valve (SCSSV) 144

  12. Vertical Tree Tubing Hanger Plug 146

  13. Horizontal Tree Crown Plugs 147

  
  

  Introduction

  
  

  The safe construction and operation of a deepwater (DW) well requires proper well design and operational procedures. The complexity of DW operations demands an in-depth understanding of the DW environment (e.g., metocean, marine, and subsurface) as well as DW procedures and equipment. This combined understanding is used to provide the basis of design for DW subsea wells.

  
  

  This recommended practice provides well design and operational considerations to assist an experienced well (drilling or completion) engineer to safely design and construct any DW well drilled with subsea blowout preventers (BOPs). This document also addresses riserless drilling considerations prior to the installation of the subsea BOPs.

  
  

  vi

  Deepwater Well Design and Construction

  
  

  1 Scope

  
  

  The complexity of deepwater (DW) operations requires a thorough understanding of well design criteria and associated equipment. This recommended practice (RP) provides engineers a reference for DW well design as well as drilling and completion operations. This RP will also be useful to support internal reviews, internal approvals, contractor engagements, and regulatory approvals.

  
  

  The scope of this RP is to discuss DW drilling and completion activities performed on wells that are constructed using subsea blowout preventers (BOPs) with a subsea wellhead. This document addresses the following.

  
  

• Identifies the appropriate barrier and load case considerations to maintain well control during DW well operations (drilling, suspension, completion, production, and abandonment).

  
  

• Supplements barrier documentation in API 65-2 with a more detailed description of barriers and discussion of the philosophy, number, type, testing, and management required to maintain well control. This document also supplements the barrier documentation in API 90 in regard to annular pressure buildup (APB). Abandonment barrier requirements are described for use when designing the well.

  
  

• Discusses load assumptions, resistance assumptions, and methodologies commonly used to achieve well designs with high reliability. The load case discussion includes less obvious events that can arise when unexpected circumstances are combined.

  
  

• Describes the risk assessment and mitigation practices commonly implemented during DW casing and equipment installation operations.

  
  

  The purpose of this document is to enhance safety and minimize the likelihood of loss of well control or damage to the environment. These practices are generally intended to apply to subsea wells drilled with subsea BOPs in any water depth. Some of the descriptions of rig hardware and operations, such as remotely operated vehicles (ROVs), are less relevant in shallower water depths [e.g. less than 500 ft (152 m)]. In these shallower water depths the operator may substitute alternative hardware or operations that maintain safety and system reliability.

  
  

  The following aspects of DW well design and construction are outside the scope of this document.

  
  

• Detailed casing design load case definitions (does not include specific casing designs or design factors). Individual companies combine differing severities of loads and resistances or differing calculation methods to achieve designs with similar high levels of reliability.

  
  

• Wells drilled and/or completed with a surface BOP and high pressure riser from a floating production system; however, considerations for wells predrilled with floating rigs to be completed to a floating production system are included.

  
  

• Well control procedures (refer to API 59 for well control information).

  
  

• Managed pressure drilling operations (including dual gradient drilling).

  
  

• Production operations and fluids handling downstream of the tree (subsea facilities/subsea architecture, and surface facilities/offloading hydrocarbons).

  
  

• Intervention operations.

  
  

• Quality assurance (QA) programs.

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