Design and Operation of Solution-mined Salt Caverns

Used for Liquid Hydrocarbon Storage

API RECOMMENDED PRACTICE 1115 SECOND EDITION, NOVEMBER 2018

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Foreword

This document supersedes both the 2nd Edition of API Recommended Practice 1114, and the 1st edition of API Recommended Practice 1115.

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iii

Contents

Page

1. Scope 1

   1. Overview 1

   2. Applicable Rules and Regulations 1

2. Normative References 2

3. Terms, Definitions, Acronyms, and Abbreviations 2

   1. Terms and Definitions 2

   2. Acronyms and Abbreviations 9

4. Overview of Underground Liquids Storage 10

   1. General 10

   2. Functional Integrity 10

   3. Overview of Major Steps in the Development of Liquid Storage Caverns 10

5. Geological and Geomechanical Evaluation 13

   1. General Considerations 13

   2. Site Selection Criteria 13

   3. Geologic Site Characterization 14

   4. Geomechanical Site Evaluation 22

   5. Assessment of Cavern Stability and Geomechanical Performance 27

6. Cavern and Well Design 28

   1. General 28

   2. Cavern Spacing Constraints 30

   3. Hole Section Design 31

   4. Casing Design 34

   5. Wellhead Design 37

   6. Storage Volume 41

   7. Displacement-fluid Characteristics 42

   8. Product Characteristics 42

7. Drilling 42

   1. Preliminary Considerations 42

   2. Rig and Equipment 43

   3. Drilling Fluids 45

   4. Drilling Guidelines 46

   5. Logging 47

   6. Casing Handling and Running 48

   7. Cementing 48

   8. Completion 52

8. Cavern Solution Mining 52

   1. General 52

   2. Cavern Solution-mining Design 52

   3. Cavern Development Phases and Control 56

   4. Instrumentation, Control, and Shut Down 64

   5. Cavern Monitoring 65

   6. Workovers During Solution Mining 67

   7. Workover to Configure for Liquid Hydrocarbon Storage Service 68

   8. Existing Cavern Conversions 69

   9. Cavern Enlargement 71

9. Liquid Hydrocarbon Storage Operations 71

   v

   Contents

   Page

   1. Facilities and Equipment 71

   2. Minimum and Maximum Operating Limits 74

   3. Backwash Operations 75

   4. Equipment 75

   5. Instrumentation, Control, and Shutdown 76

   6. Inspection and Testing 77

   7. Workovers 78

   8. Site Security and Safety 79

   9. Operating Administration 81

10. Cavern Integrity Monitoring 83

    1. General 83

    2. Holistic and Comprehensive Approach 86

    3. Integrity Monitoring Program 86

    4. Review of Integrity Monitoring Methods 86

    5. Inactive Caverns 86

11. Cavern Abandonment 87

    1. Objectives 87

    2. Abandonment Design 87

    3. Removal of Stored Product 87

    4. Wellbore Integrity Test 87

    5. Removal of Downhole Equipment 87

    6. Production Casing Inspection 88

    7. Sonar Survey 88

12. Risk Management for Liquid Hydrocarbon Storage Operations 88

    1. General 88

    2. Risk Management 88

    3. Data Collection and Integration 88

    4. Threat and Hazard Identification and Analysis 88

    5. Preventive and Mitigative (P&M) Measures 89

    6. Risk Assessment 94

    7. Periodic Review and Reassessment 94

    8. Recordkeeping 95

Annex A (informative) Open-hole Well Logs 96

Annex B (normative) Integrity Monitoring Methods 99

Annex C (informative) Brine Tables 102

Bibliography 103

Figures

1. Simplified Salt Dome Storage Cavern Schematic 12

2. Typical Cemented Casing Program for Domal Salt 33

3. Typical Solution-mining Wellhead 38

4. Typical Liquid Hydrocarbon Storage Wellhead with Hanging String 39

5. Solution-mining Methods 55

6. Cavern Development Phases 57

Tables

1. Integrity Monitoring Methods 84

2. Potential Threats and Consequences/Preventive and Mitigative Programs 89

vi

Design and Operation of Solution-mined Salt Caverns Used for Liquid Hydrocarbon Storage

1. Scope

   This recommended practice (RP) provides the functional recommendations for salt cavern facilities used for liquid hydrocarbon storage service and covers facility geomechanical assessments, cavern well design and drilling, and solution mining techniques and operations, including monitoring and maintenance practices. This RP is based on the accumulated knowledge and experience of geologists, engineers, and other personnel in the liquid hydrocarbon storage industry and promotes public safety by providing a set of industry accepted design and operation guidelines. This RP recognizes the nature of subsurface geological diversity and stresses the need for in-depth, site-specific geomechanical assessments, with a goal of long-term facility integrity and safety.

   
   

   This RP includes the cavern well system (wellhead, wellbore, and cavern) from the emergency shutdown (ESD) valve to the cavern and facilities that have a significant impact on the safety and integrity of the cavern system. It also includes a structure for risk assessment for salt cavern facilities used for liquid hydrocarbon storage service.

   
   

   This RP may be applied to existing facilities at the discretion of the user.

   
   

   This RP does not apply to caverns used for the storage of gaseous products, natural gas, brine production, or waste disposal, nor to caverns that are mechanically mined, or depleted hydrocarbon or aquifer underground gas storage systems. This RP does not cover facility piping.

   
   

   1. Overview

      
      

      Storage of liquid hydrocarbons in solution-mined salt caverns has been utilized in the United States since the late 1940s. Today, storage of liquid hydrocarbons in caverns developed in both domal and bedded salt formations is utilized throughout the world.

      
      

      Salt caverns can act as long-term, seasonal storage vessels; or they may serve as short-term, operational storage. Caverns can also be inserted into the production plant/pipeline systems to prevent supply interruptions when maintenance or emergency shutdowns occur, or to “float” on pipelines to optimize operations.

      
      

      Storage of liquid hydrocarbons in a salt cavern may require careful review to ensure that the product is compatible with the salt. Chemical and physical properties of the salt at the cavern depth and at the pressure anticipated should be reviewed to verify that unwanted chemical or physical reactions do not occur. Incompatibility of product and salt is rarely a problem for most hydrocarbons. Examples of exceptions are storage in salt caverns where sulfides are present and storage of jet fuels with de-icing agents that absorb water.

      
      

      In summary, storage of liquid hydrocarbons in salt caverns can provide an economical, safe, and environmentally sound method to store large quantities of compatible materials.

      
      

   2. Applicable Rules and Regulations

This document was written to provide a technical reference for the development and operations of solution-mined salt caverns used for the storage of liquid hydrocarbons, and is not intended to represent or reflect any regulatory requirement. Depending on location and nature of the project, the recommended practices herein may address items that are in conflict with some regulatory requirements. If this occurs, the regulatory requirement supersedes the recommended practice unless an appropriate waiver or variance is granted from the issuing agency. A thorough review of the applicable rules and regulations is to be performed prior to the design of solution-mined liquid storage caverns to ensure ongoing compliance.