Well integrity

There are different definitions of what is Well Integrity. The most widely accepted definition is given by NORSOK D-010: “Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well.”

Other accepted definition is given by ISO TS 16530-2 “Containment and the prevention of the escape of fluids (i.e. liquids or gases) to subterranean formations or surface.”

Well Integrity is a multidisciplinary approach. Therefore, well integrity engineers need to interact constantly with different disciplines to assess the status of well barriers and well barrier envelopes at all times.

Well Integrity operating philosophy

The well integrity operating philosophy is an important element that one should carefully consider with respect to how to manage the risk of loss of containment and overexpose oneself with additional risk by frequent well visits and interventions that brings exposure to the people and environment by doing these activities. The overall process should fit together. It is of little use to define a meantime to repair for failed barrier components and not have supporting critical spares or competent resources in place to able to respond to such an event. The philosophy should be aligned with risk exposure and be clearly under scribed by the process owner.

Roles and Responsibilities

Personnel competency and training

There are a number of competency assurance processes available. There are not many that are specific to well integrity, but the below example of a competence matrix (part 1&2) on how one may look, The assurance and training is similar to any other educational system in that there is a theoretical level and a practical level. Both are equally important. The verification process of the ability to perform a certain task is a must that one needs to consider and assure himself of.

The categories of people are subjective in example as each organization is different. This in itself is not an issue as one can adapt the matrix and make it suitable. The main issue is whatever task or activity is assigned in the well integrity process, one must assign the appropriate competencies for that task, assure that these competencies are in place, and that they are validated and maintained.

The above is applicable for operator staff or contractor staff. There may be some regulated standards available like Opito that is used in the North Sea.

Further, there are websites on well integrity that are a maintained by others such as http://www.wellintegrity.net/.

Standards and governances

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Well integrity management systems

A Well Integrity Management System (WIMS) is a meaningful solution to define the commitments, requirements and responsibilities of an organization to manage the risk of loss of well containment over the well lifecycle. The tasks necessary to deliver well integrity, and the roles accountable and responsible for delivery, are specified in a WIMS document. To operationalize the management system, software tools can be used. These have various forms from simple solutions managed with a spreadsheet to more complex systems managed using self-built or commercially available electronic management systems.

The objective of a WIMS is to specify requirements necessary for delivery of well integrity, including:

• Well integrity refers to maintaining full control of fluids within a well at all times, in order to prevent unintended fluid movement or loss of containment to the environment.
• Well integrity policy defines commitments and obligations to safeguard health, safety, environment, assets, and reputation.
• WIMS is the system that assures that well integrity is maintained throughout the well life cycle by the application of a combination of technical, operational, and organizational processes.

Commercially available well integrity management systems software includes:

• Expro SafeWells – A smarter adaptable Well Integrity Data Management web application
• Wood iWIT – comprehensive, web-based software toolkit to monitor well integrity, manage data, and ensure compliance
• Peloton WRMS (WellMaster Reliability Database)
• Oxand - Simeo risk based assessment
• RIFTS - mainly artificial lift, structural under development (JIP)
• OREDA - Offshore and Onshore reliability data
• Halliburton - Landmark - DecisionSpace Well Integrity Management (DSWIM)
• Yuit SWIS - Smart Well Integrity System
• Peloton Well Integrity (enhanced with Well Barrier and Integrity Program)
• Wellbarrier - A Schlumberger Technology
• Well-Scape WIMS - Cloud based WIMS and Mobile App for efficient wellsite data collection

• 

  Example of a well integrity management system lifecycle.

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Elements of the well integrity management system

• Wells ownership over the lifecycle for wells that are:
  • Developed
  • Acquired
  • Divested
  • Suspended
  • Closed in
  • Operated
  • Exploration
  • Abandoned by company.
• Organizational structure with roles:
  • Responsibilities
  • Competencies
• Risk assessment with risk register that:
  • Defines the risk
  • Mitigations for the hazards that are to be managed
• Well types with:
  • Well barriers
  • Well barrier envelopes that control hazards
• Performance standards that:
  • Defines the requirements to maintain the well barriers within its operating limits.
• Well barrier verification, or assurance processes that:
  • Assures the mechanical status of the well is maintained on a defined risk
• Underlying processes like:
  • Reporting
  • Documentation
  • Management of change
  • Continuous improvement
  • Auditing processes.

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Objective of the well integrity management system

The overall objective is to give transparency on how risk is managed. One way to achieve this transparency is to benchmark other operators to verifing how effective the well integrity management system performs. Another way is to compare the system to industry standards (e.g. The NACE's Petroleum and natural gas industries--Well integrity--Part 1, ISO 16530-1).

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An effective well integrity management system

An effective well integrity management system uses a risk based matrix that will demonstrate how to manage risk. This risk-based matrix is based on "as low as reasonably practical" ALARP . Well operating limits is a combination of the criteria established to ensure that the well remains within its design limits in order to maintain well integrity throughout the well life cycle. For each well type, it is normal when changes occur and the well operating limits should be checked.

To assure well operating limits, some parameters could be monitored over the well life cycle when the well is constructed, operated, shut-in or suspended;

• requirements for any threshold settings for the well limits;
• actions that should be taken in the event a well parameter is approaching its defined threshold;
• actions, notifications and investigations required if well limit thresholds are exceeded;
• safety systems that are necessary to ensure parameters stay

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Risk assessment

A Risk Assessment is a procedure to determine the quantitative or qualitative value of a risk or threat to a specific situation. Risk can be defined as a combination of both the severity of the consequences of an event and the likelihood or probability that the event will occur. Risk increases with increasing severity and/or likelihood. Risk tolerance and risk rank category definitions can vary by company and location. However, it is an industry-accepted practice to require prevention or mitigation for significant and/or high risk category wells.

One very general but accepted definition for a high risk well is: “A well in which that last barrier is under threat of being compromised.” Each company should create their own specific definitions for well risk based on operating area, well stock, and risk tolerance. There are numerous risk assessment methods available to facilitate the determination of well risk and a few of those methods are summarized below.

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Quantitative risk assessment (QRA)

Quantitative Risk Assessment (QRA) is a method of risk assessment based on numerical probability using historical data and reliability models. This method is commonly used for hydrocarbon processing facilities and oil pipeline systems. The challenge for using a QRA for well integrity is the availability and applicability of well failure and reliability data for use in a risk model. Even with a perfect model, initial conditions and boundary conditions must be correct or the prediction will be flawed.

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Qualitative risk assessment

A Qualitative Risk Assessment is a more conventional method for well integrity. It is primarily based on experience and the application of good engineering judgment. Qualitative Risk Assessments are easier to execute but are limited by the experience and knowledge of the people completing the assessment.

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QRA/Qualitative hybrid

Due to a lack of well integrity reliability data for QRAs, many well integrity risk assessments are QRA/Qualitative hybrids based on known failure data, rules, procedures, and risk matrices rather than using straight qualitative or QRA analyses. One such hybrid method documented in 142854-PA SPE Journal Paper – 2012 is a hybrid risk assessment method that uses a qualitative, team-based brainstorming format following the “what if” methodology to identify hazards associated with known or predetermined well-barrier failure modes and likelihoods from a known well stock. This method uses a risk matrix with customized likelihood and consequences as shown in the sample below.

Considerations for Risk Assessments

Components that contribute to the risk profile of a well or number off wells that determine how the risk needs to be managed could be:

• Outflow potential to surface or subsurface environments
• Fluid types and composition, H2s, Co2, gas, oil, dehydration water etcetra’s
• Location, subsea, offshore, swamp, land, urban, natural reserve etcetra’s
• Earth model, subsidence, earth quakes, permafrost
• Collision from vessels, fishing, trucks, landslides, intervention activities

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Well design, well construction, and barrier requirements

During well design and construction, the barrier requirements are driven by the input of the basis of design and the identified hazards. These hazards can change over the life cycle of the well or may actually be introduced during the construction of the well. The design and construction process is the main element that drives how the well needs to be operated, maintained, or abandoned. There is with each field or well development plan the element of economics, the time line to deliver, or earth model hazards that are encountered that may result in decisions that affect well integrity or well operating limits. From a well integrity management perspective, the relevancy is to understand the risk associated with exposure to certain hazards and that these are clearly defined in the well operating limits at well handover so that mitigating controls can be applied over the wells life.

Depending on the environment where the well is placed in and outflow potential of the well, with likelihood of failure and consequence of loss of containment, the well barrier requirements are defined. This is usually done in the field development stage by use of quantitative risk assessment. See below examples of various barrier designs whereby in a hydro static well, the liquid level is the primary barrier.

• 

  Barrier designs

Some examples of elements that may have to be managed during the design construct of well barriers to assure them over the well lifecycle are:

• Internal oxygen-related corrosion
  • CO2 corrosion
  • H2S corrosion
  • chloride stress cracking
  • stress cracking caused by bromide mud and thread compound
  • microbial-induced corrosion (MIC)
  • other chemical corrosion
  • acid corrosion (e.g. from stimulation fluids)
• External corrosion as result of
  • aquifers
  • surface water
  • swamp or sea environments.
• Sand/solids production
  • scale deposition
  • erosional velocities
  • formation of emulsion
  • scale
  • wax and hydrate deposits.
• Compatibility between components, electrolytic corrosion.
• Load cases as result of
  • thermal
  • fatigue
  • subsidence
  • stimulation
  • well kill
  • injection
  • production
  • evacuation
  • trapped pressures
  • casing wear.
• Earth model fractures
  • pore pressures
  • permafrost movement
  • squeezing chalks
  • salts
  • earthquake
  • subsidence.
• Zonal isolation placement and verification of isolation methods.

Typically well head valves and Xmas trees are single barrier elements as they use floating gates and seats that hold in one direction that results in valve bonnet , grease nipple, and stem packing to be under pressure at all times. See example of a typical gate valve below. When designing the well and its barriers, this needs to be taken into consideration.

The well barrier design and construction process objective should address the issues such that the barriers over the well life cycle assure containment that can effectively be managed and verified. This statement is a challenge in itself as many wells have issues over the life cycle as things were not clear from beginning or changes occurred or well was not designed and constructed as intended. The process of well integrity management is to understand the risks and address these by managing the well barriers within its operating limits to prevent loss of containment.

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Managing abnormal casing pressure and sustained casing pressure

Wells are designed and constructed to allow for operation with some pressure on the annuli. This pressure only becomes a problem when there is an indication of a well integrity issue or if the maximum allowable wellhead operating pressure (MAWOP) has been exceeded. Depending on the source of the pressure and applicable area regulations the appropriate operator response may differ. Therefor it is important to monitor annular pressure on a recurring basis and understand the source of the pressure.

There are three main sources for annulus pressure:

1. Intentionally applied pressure – define as annulus pressure that is intentionally used by the operator for a specific purpose.
2. Thermally induced pressure – define as pressure that results from thermal expansion of trapped fluid in the annulus.
3. Sustained casing pressure - define as unintended pressure in an annulus that is not thermally induce nor intentionally applied. It pressure caused from communication to formation or another annulus through a defective or failed barrier.

The cause of annulus pressure can be evaluated by reviewing well records and temperature and pressure trends, relieving or bleeding the pressure, and then monitoring the build-up rate.

Barrier Verification/ Barrier Diagnostics

At various phases of a well’s life cycle, the integrity of the well barriers and/or well barrier elements should be verified. The verification may involve pressure measurement, tagging, pressure testing, leak testing, leak off testing, well logging or flow rate measurement. If anomalous behavior is observed then a diagnostic process is initiated, usually to determine the location and magnitude of the leak.

Typical key barrier verification steps and techniques during various well life cycle phases are as follows:

Life Cycle Phase	Well Barrier Element(s)	Barrier Verification Examples
Well Construction or Workover
	Fluid column	Fluid density, fluid loss rate, fluid level
	BOP	Pressure test, function test
	FOSV or IBOP	Pressure test, function test
	Casing and liner	Pressure test Well logging - ultrasonic
	Wellhead / casing hanger	Pressure test
	Geological formation	Leak off test or formation integrity test Well logging – ultrasonic or electromagnetic wall thickness, mechanical caliper
	Liner hanger / liner	Pressure test Negative (inflow) test
	Annular Cement	Pressure measurements – calculated cement column height Well logging – acoustic and ultrasonic tools
	Tubing	Pressure test - internal or external
	Production packer	Pressure test – from above or below packer element
	Subsurface safety valve	Leak test, function test
	Xmas tree	Pressure test, leak test, function test
Well Operations
	Casing and liner	Annulus pressure monitoring Annulus bleed down test Annulus pressure test
	Completion string	Annulus pressure monitoring Pressure test – tubing or annulus Leak off test (annulus bleed down) Acoustic fluid level survey
	Subsurface safety valve	Leak test, function test Control line pressure test
	Gas lift valve	Leak off test (annulus bleed down) Acoustic fluid level survey
	Wellhead / casing hanger	Pressure test, leak test, function test, visual inspection Infrared thermal imaging, casing vent monitoring
	Xmas tree	Pressure test, leak test, function test, visual inspection, ultrasonic wall thickness measurement Infrared thermal imaging
Well Intervention (Rigless)
	BOP	Pressure test, function test
	Pressure control equipment	Pressure test
	Completion string (including casing and liner below tubing tailpipe)	Well logging – mechanical caliper, ultrasonic and electromagnetic wall thickness, ultrasonic leak detection, pulsed neutron log, magnetic flux leakage, temperature, production log, video or acoustic tools, fiber optic distributed acoustic and temperature log Pressure test - against downhole plug or straddle tool
Well Abandonment
	Casing and liner	Pressure test Well logging – mechanical caliper, ultrasonic and electromagnetic wall thickness
	Annular Cement	Pressure measurements – calculated cement column height Well logging – acoustic and ultrasonic tools
	Cement plug	Tag top of cement
		Pressure test
		Negative (inflow) test

To determine whether the well barrier has an acceptable level of integrity, the barrier verification results are compared with the performance standards (or acceptance criteria) that apply to that well. Some oil and gas companies have their own in-house standards and some jurisdictions have regulatory regimes that prescribe the minimum verification requirements for certain well barrier elements, for example the length or height of cement plugs. Companies commonly adopt performance standards based on the following publically available reference documents.

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• Well integrity – Part 1: Life cycle governance, International Standard ISO 16530-1 First edition 2017-03

• Well integrity in drilling and well operations, NORSOK Standard D-010 Rev. 4. June 2013 , (Web)
• Guidelines for the Abandonment of Wells, Issue 5, July 2015, Oil & Gas UK
• Well Life Cycle Guidelines, Issue 4, March 2019, Oil & Gas UK

Since these documents are not consistent in all aspects, it is important for a company’s well engineering management system and/or well integrity management system to explicitly define the well barrier elements (and/or safety critical elements) and the performance standards that shall apply.

The performance standards need not be uniform across all wells operated by a company or within a region, and can vary after considerably based on the risk profiles for different well types and the specific regulatory regimes that apply. An example performance standard for well safety critical elements provided in ISO / TS 16530-1 for the operational phase is reproduced below.

Description	Performance monitoring requirement	Units of Measure	Acceptance criteria example
Well Head/Tree Visual Inspection: There shall be no leaks/weeps of the well head/tree, valve and instrument connections. (Visual Inspection)	Acceptable visual inspection	No leaks	Zero
Wellhead/Tree valve operability: All wellhead/tree valves shall be operable in accordance with manufacturer defined specifications (number of turns).	Acceptable test / operate on demand as per manufacturer specification	Number of turns	18 3/4 turns
Wellhead/Tree valve Actuation : Actuated wellhead/tree valves shall close within the required time as defined by operator in the well hook up cause and effect requirements for shutdown based on API 14 B.	Acceptable response test	Time	30 seconds
Wellhead/Tree valve Leakage Rate: The valve leakage rate is not greater than the corresponding allowable leakage rate as specified by operator based on API 14 B	Acceptable test / leak rate	Ambient volume/ time	0,425M3/min
Annular Safety Valve integrity: The ASV performs within the parameters specified by the operator based on API 14 B	Acceptable test Operates on demand records available	Pressure limit	xx MPa
Annulus Integrity Management (1): The annulus pressures are to be within specified values for Maximum Allowable Annulus Surface Pressure (MAASP)/Trigger and Minimum Values	Operates within MAASP records available	Pressure limit	xx MPa
Annulus Integrity Management (2): The annulus pressure monitoring equipment is calibrated correctly and alarms (where fitted) operate at the required set points or pressures are recorded manually on regular intervals.	Acceptable test Operates on demand records available	Accuracy	Percentage
Annulus Integrity Management (3): The annulus pressures test is to be within the wells operating envelop as defined by Operator.	Acceptable test Operates on demand records available	Pressure test	xx MPa
Sub Surface Safety Valves (SSSVs) Integrity: The SSSV performs within the parameters specified by Operator.	Acceptable test Operates on demand	Leak test	0,425M3/min
Well Plug(s) Integrity Test : The well plugs perform within the parameters specified by Operator.	Acceptable test Operates on demand	Leak test	0,425M3/min
Gas Lift Valve (GLV) / Tubing Integrity Test : The GLVs and tubing perform within the parameters specified by Operator.	GLV Tubing to annulus test acceptable	Inflow test	0,425M3/min
Hanger neck seal, control line feed through, electrical feed through and DASF / adaptor spool seal area’s : The component pressures test is to be within the wells operating envelop as specified by Operator.	Acceptable test Operates on demand	Pressure test	xx MPa
Shutdowns of artificial lift Pumps Electrical submersible pumps (ESP’s) / Beam pumps / Electrical Submersible Positive Cavity Pumps (ESPCP’s) / Positive Cavity Pumps (PCPS) /Jet pumps gas lift systems. Artificial lift systems that have capability to overpressure flow line / wellheads or other well components, shutdown test is to be within defined cause and effect diagram parameters.	Acceptable test Operates on demand	shutdown test	30 seconds
Location safety valve or production wing valve: Operates as defined in cause and effect s diagram as defined by well operator.	Acceptable test Operates on demand	shutdown test	30 seconds
Operating envelop of Injection wells: Maximum allowable injecting pressure as defined by Operator.	Operating limit of pressure of injection pressure based on MAASP of well bore	Pressure limit	xx MPa
Steam wells Maximum allowable pressure / temperature as defined by Operator.	Operating limit of pressure of injection pressure / temperature based on Maasp & temperature limitations of well bore	Pressure + Temperature limit	xx MPa / deg Celsius

Other useful reference documents include:

• API RP 90-2: Annular Casing Pressure Management for Onshore Wells (to be issued)
• API RP 96, First Edition, 2013 Deepwater Well Design and Construction (Web)
• API Std 53, Fourth Edition, 2012 Blowout Prevention Equipment Systems for Drilling Wells
• API Std 65 Part 2, 2nd Edition, 2010 Isolating Potential Flow Zones During Well Construction, 2nd Edition (Web)
• Norwegian Oil and Gas Association Recommended Guidelines for Well Integrity No.: 117 Established Revision no 4 2011 (PDF)
• SPE 102815 Applied Ultrasonic Technology in Wellbore Leak Detection and Case Histories in Alaska North Slope Wells. Johns et al 2006 (Web)
• SPE 130395 Case Study: Shallow Surface Casing Corrosion Mitigation Evaluation, Blakney et al 2010 (Web)
• SPE 163938 Strategic Rigless Approach in Identifying and Curing Complex and Multiple Completion Leaks in Malaysia, Nussbaum et al, 2006 (Web)
• Oil and Gas UK Guidelines for Suspension and Abandonment of Wells, Issue 4, July 2012
• OSCR UK Offshore Installations (Safety Case) Regulations 2005 (OSCR)
• ISO 31000 Risk Management
• ISO15156-1:2015 Materials for use in H2S-containing environments in oil and gas production
• ISO 10419 Installation, maintenance and repair of surface safety valves and underwater safety valves offshore
• API 6A: "Specification for Wellhead and Christmas Tree Equipment"
• API RP 14B: "Design, Installation, Repair and Operation of Subsurface Safety Valve Systems"
• API RP 14C: "Recommended Practice for Analysis, Design, Installation, and Testing of Basic Surface Safety Systems for Offshore Production Platforms"
• API RP 14H: "Recommended Practice for Installation, Maintenance, and Repair of Surface Safety Valves and Underwater Safety Valves Offshore"
• API RP 57: "Offshore Well Completion, Servicing, Workover, and Plug and Abandonment Operations"

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Noteworthy papers in OnePetro

Dethlefs, J. and Chastain, B. 2012. Assessing Well-Integrity Risk: A Qualitative Model. SPE Drill & Compl 27 (02): 294-302. SPE-142854-PA. http://dx.doi.org/10.2118/142854-PA.

King, G.E. and Valencia, R.L. 2014. Environmental Risk and Well Integrity of Plugged and Abandoned Wells. Presented at the SPE Annual Technical Conference and Exhibition, Amsterdam, 27-29 October. SPE-170949-MS. http://dx.doi.org/10.2118/170949-MS.

Singh, S.K., Subekti, H., Al-Asmakh, M., et al. 2012. An Integrated Approach To Well Integrity Evaluation Via Reliability Assessment Of Well Integrity Tools And Methods: Results From Dukhan Field, Qatar. Presented at the SPE International Production and Operations Conference & Exhibition, Doha, Qatar, 14-16 May. SPE-156052-MS. http://dx.doi.org/10.2118/156052-MS.

Vignes, B., and Aadnøy, B.S. 2010. Well-Integrity Issues Offshore Norway. SPE Prod & Oper 25 (2): 145-150. SPE-112535-PA. http://dx.doi.org/10.2118/112535-PA.

Watson, V. 2010. A Quantitative Risk Assessment Approach. SPE International Conference on Health, Safety and Environment in Oil and Gas Exploration and Production, Rio de Janeiro, 12-14 April. SPE-127213-MS. http://dx.doi.org/10.2118/127213-MS.

Wilson, V. A. 2014. HSE and Well Integrity: Friends or Foes? SPE International Conference on Health, Safety, and Environment, Long Beach, California, USA, 17-19 March. SPE-168407-MS. http://dx.doi.org/10.2118/168407-MS.

SPE papers grouped by conferences: https://www.onepetro.org/conferences/spe

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Online multimedia

Hopmans, Paul. 2013. Journey of Well Integrity. https://webevents.spe.org/products/journey-of-well-integrity

Dethlefs, Jerry. Near Surface External Casing Corrosion; Cause, Remediation and Mitigation. http://www.spe.org/dl/docs/2011/Dethlefs.pdf

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External links

SPE. Well Integrity Technical Section. http://connect.spe.org/WellIntegrity/home.

Page champions

MJ Loveland - Well Integrity Supervisor ConocoPhillips (retired)