Operation, Maintenance, Surveillance, and Troubleshooting of Gas-lift Installations

API RECOMMENDED PRACTICE 19G5 FIRST EDITION, JULY 2019

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Foreword

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iii

Contents

Page

1. Scope 1

2. Terms, Definitions, and Abbreviations 1

   1. Terms and Definitions 1

   2. Abbreviations 2

3. Gas-lift Operating System Components and Potential Problems 2

   1. Purpose 2

   2. Gas-lift System Components 3

   3. Gas-lift System Operating Problems 3

   4. Surface Facility Problems 4

   5. Metering and Control Problems 5

   6. Gas-lift Valve Problems 6

   7. Well Equipment Problems 6

   8. Gathering System Problems 7

   9. Well Testing Problems 8

   10. Production Handling Problems 8

   11. Information Handling Problems 9

   12. Surveillance and Control Problems 10

4. Gas-lift Operating Problems 10

   1. Purpose 10

   2. Under-lifted and Over-lifted Wells 11

   3. Ineffective Gas Distribution 18

   4. Unstable Gas-lift Operation 18

   5. Types and Causes of Unstable Operation 20

   6. Other Problems 23

5. Surface Gas-lift Compression, Dehydration, and Distribution 24

   1. Purpose24

   2. Compression Facility 25

   3. Gas Dehydration Facility 27

   4. Gas-lift Distribution System 29

6. Gas Injection Metering and Control 31

   1. Purpose 31

   2. Gas Metering 31

   3. Injection Control 33

7. Gas-lift Valves 36

   1. Purpose 36

   2. Unloading Valves 36

   3. Operating Valve(s) 38

8. Well Equipment Tubulars, Completion, and Wellhead 39

   1. Purpose 39

   2. Casing/Tubing Annulus 39

   3. Tubing 41

   4. Completion 42

   5. Wellhead 44

   6. Wellhead Monitoring and Control 45

9. Gathering System-flowline and Manifold 47

   v

   Contents

   Page

   1. Purpose 47

   2. Flowline 48

   3. Manifold 50

10. Well Production Rate Testing 51

    1. Purpose 51

    2. Well Testing 51

    3. Well Test Equipment 57

    4. Well Test Measurements 59

11. Production Handling System 61

    1. Purpose 61

    2. Oil Handling System 62

    3. Water Handling System 62

    4. Gas Handling System 62

12. Guidelines for Collecting and Using Operating Information 63

    1. Purpose 63

    2. Well Test Information 63

    3. Downtime Information 66

    4. Pressure and Temperature Surveys 67

    5. Injection Pressure and Rate Measurements 73

    6. Wellhead Production Pressure, Temperature, and Rate 74

13. Manual and Automated Well Operation and Control 76

    1. Purpose 76

    2. Manual Operations 76

    3. Automated Operations 77

14. Procedures for Initial Unloading and Kickoff 79

    1. Purpose 79

    2. General Unloading Recommendations 79

    3. Unloading Continuous Gas-lift Wells 80

    4. Restarting (Kick-off) Continuous Gas-lift Wells 82

    5. Unloading Intermittent Gas-lift Wells 82

    6. Restarting (Kick-off) Intermittent Gas-lift Wells 84

15. Procedures for Adjusting (Fine-tuning) Gas-lift Injection Rates 84

    1. Purpose 84

    2. Continuous Gas-lift Wells with Steady Pressure 84

    3. Continuous Gas-lift Wells with Variable Injection Pressures 85

    4. Intermittent Wells with Time Cycle Control 85

    5. Intermittent Wells with Choke Control 86

    6. Intermittent Wells with Automatic Control 87

    7. Flowline Chokes 87

Bibliography 88

Figures

1. Gas-lift System Components 5

2. Problem of Injecting Gas through an Upper Gas-lift Valve 13

3. Problem of Under-injection—Injecting Too Little Gas 14

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   Contents

   
   

   Page

4. Over-injection of Gas 15

5. Determining the Optimum Gas Injection Rate 16

6. High Injection Pressure Causing an Upper Valve to Open 17

7. Under-injection—Causing Operating Valve to Flood 22

8. Hydrate Conditions 27

9. Water Content vs Temperature and Pressure 28

10. Finger Distribution System 29

11. Looped Distribution System 30

12. Adjustable Choke for Continuous Gas-lift Control 84

Tables

1. Well Test Data Expressed in Oil Field Units 65

2. Well Test Data Expressed in Metric Units 65

vii

Introduction

These recommended practices and requirements are offered to assist gas-lift system operators, analysts, technicians, engineers, and others in understanding how to effectively plan, operate, maintain, troubleshoot, and provide surveillance of gas-lift systems and gas-lift wells.

These recommended practices discuss continuous gas-lift with injection down the casing/tubing annulus and production up the tubing. Annular flow gas-lift (injection down the tubing and production up the annulus), dual gas-lift (two tubing strings in the same casing), and intermittent gas-lift are mentioned; however, most of the discussion focuses on conventional continuous gas-lift. Many of the recommended practices in this document can be pertinent to the other forms of gas-lift, but they should be considered and used with caution. Other API recommended practices address dual gas-lift (API 19G9) and intermittent gas-lift (API 19G10).

This document includes the following.

• Gas-lift operating system components and potential problems.

  
  

  Sections 3 through 13 describe the several components of an operating gas-lift system and discuss a number of problems that can be encountered and addressed to operate a gas-lift system effectively and efficiently. These sections may be used for:

  
  

  • part of a training course dealing with gas-lift system operation;

    
    

  • a review before beginning a major gas-lift system study;

    
    

  • a review before designing or modeling a gas-lift system, or both;

    
    

  • a review before trying to troubleshoot difficult gas-lift system problems.

    
    

• Recommended practices for gas-lift operation, maintenance, surveillance, and troubleshooting.

  
  

  Sections 14 and 15 are revisions/upgrades of information that has been in existence since the first edition of this document. These sections contain recommended practices for common gas-lift operations:

  
  

  • initial unloading of the completion or workover fluid from the annulus of the gas-lift well;

    
    

  • restarting or kickoff after a period of downtime;

    
    

  • adjusting or fine-tuning the gas injection rate for optimum operation.

    
    

    These sections discuss commonly used gas-lift troubleshooting tools. They conclude with sections that review the potential locations of gas-lift problems, a table of possible causes and cures of some common gas-lift system problems, and a troubleshooting checklist.

    
    

    These sections are recommended for use as:

    
    

• part of a training course dealing with gas-lift system operation;

  
  

• part of a training course dealing with gas-lift system maintenance;

  
  

• a review before trying to troubleshoot a difficult gas-lift operating problem.

viii

Operation, Maintenance, Surveillance, and Troubleshooting of Gas-lift Installations

1. Scope

   This recommended practice (RP) provides guidance, background, and requirements for the application and use of gas-lift wells and their related systems. Discussion is included for operation, maintenance, surveillance, and troubleshooting of gas-lift wells and installations.

   
   

   This RP is intended for use by managers, production technologists, reservoir engineers, facilities engineers, production engineers, well testing engineers, well analysts, operators, and researchers who want to gain a general understanding of gas-lift wells and gas-lift operations. It can be used to prepare and present courses on gas-lift wells and operations.

   
   

   This RP focuses primarily on continuous gas-lift. However, use of intermittent gas-lift, dual gas-lift, and gas-lift for gas wells is mentioned.

   
   

2. Terms, Definitions, and Abbreviations

2.1 Terms and Definitions

For the purposes of this document, the following definitions apply.

2.1.1

bottomhole pressure BHP

The pressure measured at the midpoint of the perforated interval.

2.1.2

flowing bottomhole pressure FBHP

The pressure measured at the bottom of the well, at the midpoint of the perforations, when the well is on production.

2.1.3

inflow performance relationship IPR

The ratio of production rate (expressed in bbl/day or m3/day) divided by the pressure drawdown (static bottomhole

pressure minus flowing bottomhole pressure).

2.1.4

injection pressure operated gas-lift valve IPO gas-lift valve

A gas-lift valve where the primary opening pressure is provided by the injection pressure.

NOTE The injection pressure is provided by the casing pressure.

2.1.5

production pressure operated gas-lift valve PPO gas-lift valve

A gas-lift valve where the primary opening pressure is provided by the production pressure.

NOTE The production pressure is provided by the tubing pressure.

1