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Well integrity lifecycle
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 lifecycle or sustaining integrity in aging wells
Well lifecycles have three primary areas of focus or stages; design and construction, well operation and intervention, and abandonment. ISO 16530 delineates the lifecycles stages into six lifecycle phases, Basis of design, design, construction, operational, intervention, and abandonment.
The ability to sustain well integrity is fundamentally dependent on both the design and the operational stages. Before construction, an appropriate well design including a well barrier envelope evaluation will facilitate long term well integrity sustainability. Additionally, a suitable well integrity management system (WIMS) should assure well integrity is maintained throughout the entire well lifecycle.
Maintaining well integrity during the well operational phase also requires the practice of proactive pressure monitoring programs, barrier verification and maintenance programs. Program performance standards and test acceptance criteria are defined during the well design phase and in conjunction with any applicable regulations.
In many cases the end of well life may extend a well past the original design life so it is important to recognize that performance standards, acceptance criteria and required barrier testing and maintenance can change during the well life cycle. When pressures, performance, or barrier compliance acceptance criteria do not meet the pre-defined standards additional diagnostic tests, well intervention, repairs, and other mitigations may be required.
With aging wells and changing failure mechanisms, the challenge is to understand failure and consequences to a level that the process of managing well integrity is well understood and managed in a sustainable way.
Corrosion, erosion, or fatigue of the well barrier elements is one of the main well life cycle risks that causes loss of containment and needs to be effectively managed. Some of the following issues can contribute to the corrosion process.
- Seawater inside conductor (offshore) that corrodes the load bearing casing externally inside the conductor.
- Aquifers or surface water on shore that are not isolated and corrode the exposed casing externally.
- Mismatch of materials electrolytic corrosion
- Corrosive produced or injected fluids that cause internal corrosion
- Erosional velocities combined with sand or other solids that create material loss
- Eddy current as result of running short phased electric submersible pumps
- Sulphide reduced bacteria (SRB)
A corrosion management strategy is an important process element. It should be defined so the issue of corrosion is recognized and addressed in a structured manner to prevent structural failure and loss of containment over the lifecycle of the well.
External load bearing conduits that are crucial for containment should also be included in the corrosion management strategy and managed over the lifecycle to avoid failure or loss of containment. The management strategy should take in to account any well designs that mitigates risk, and an inspection and surveillance plan that assure the barriers in place over the well life cycle. It should also describe the contingency plans if failure occurs and the respective mitigations and who is responsible i.e. the owner of the process.
For the internal flow wetted components the strategy should contain the same elements with exception that if there is sufficient contingency in barriers like full pressure classed casing designs and additional valves you can apply a produce to fail philosophy.
Corrosion management strategy options
- Produce to fail and restore barriers with pre-determined period to minimize risk
- Design for treatment by corrosion inhibitor and maintain by surveillance
- Design with appropriate material selection that is adequate to last well life cycle
- Take gas samples from annuli for analysis. Confirm presence of H2, CO2 or O2.
Corrosion monitoring and surveillance options
Well logging and surveillance techniques may be applied. The follow list is of several different types of logs used for corrosion identification and monitoring. It may not be a complete list but does provide a good starting point for where to look for information.
- Caliper log
- Measures actual wall loss inside the pipe being evaluated. The caliper only measures wall loss on the area the caliper fingers cover and it has the risk that the trailing caliper fingers disrupt the protective coating on tubing or casing wall and cause more corrosion.
- Acoustic logs
- Historically the most routine uses for acoustic logs is reservoir and formation evaluation, however logs can give an indication cement quality and barrier failure.
- Pulsed eddy current logs
- Measure the average material wall loss picture for each tubing, casing string in the hole, effectiveness is dependent on tool, and signal interpretation capability.
Visual inspection using video surveillance, inspection of recovered material during workover, or use of corrosion coupons inside the well stream that are inspected on routine. Well elevation monitoring that will indicate subsidence of the well as result of corrosion causing casing collapse and subsidence. Unexpected changes in well elevations can be an indication of the degradation of structural support of the well and can escalate to a level that impacts the well integrity. When monitoring for subsidence or elevation of the well and its surroundings, the datum reference should be periodically verified and recorded.
These logging and surveillance techniques may be part of a pre-planned surveillance programme, or may be initiated in response to an event or an observed anomaly. Surveillance results from sample wells may be used as an input across wells of the same type in a field to predict failure rates and mitigation plans to avoid loss of containment. The surveillance experience of offset wells or fields is a very useful resource for other field developments. There are many publications on this subject that can easily explored on the internet.
Example of well head elevation monitoring for subsidence
In the case of subsea wells, operators commonly use ROV (Remotely Operated Vehicles) to perform surveillance and visual inspections of corrosion related issues. Operators should also establish routines based on local regulations or risk assessments to monitor the corrosion, subsidence and scouring around the subsea wells and structures. ROVs should measure the wellhead elevation using the datum reference taken during the installation of the conductor and wellhead. Generally, the ROV checks for:
- Scouring and/or soil deformations around wellhead.
- Any leak around subsea structure
- Degree of corrosion on subsea equipment incl. the status of the cathodic protection on the subsea equipment.
- Wellhead shape and elevation
Corrosion mitigation and remediation options
- Cathodic protection
- Is a technique used to control the corrosion of a metal surface by making it the cathode (less active) of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. Cathodic protection will only work on exposed casing, it will not be effective inside the casing if the anodes are placed externally from the well.
- Protective coatings
- There are many types, brands, and application methods for external and internal casing coatings both internally and externally. External protective coatings will reduce or stop external corrosion, but will have no effect on internal corrosion and internal coating will reduce or stop internal corrosion and have no effect on any external corrosion. Additionally, in areas where flaws, damage, or holidays may appear in the coatings surface those areas will not be protected. When relying on coatings, holidays, flaws, and damaged coating should be taken into consideration for effectiveness so that additional contingent protection methods can be applied if need.
- Oxygen removal
- Removing oxygen in an annulus or system by adding an nitrogen cap or by adding oxygen scavengers will reduce the propensity of oxygen induced corrosion.
- Sealing conductors
- Keeping oxygen out of the conductor by placing corrosion inhibiting sealant in the conductor annulus has been documented as a successful method in reducing external surface casing corrosion. Grouting or cementing the conductor annulus can also reduce corrosion as long as it is designed with low salt formulas and properly installed.
Photo of reactive corrosion inhibiting sealant placed in the conductor casing to designed to keep water an oxygen away from the surface casing.
Hydraulic fracturing impacts on integrity
Well integrity can be seriously affected by hydraulic fracturing, it starts with the way the hydraulic fracturing is designed i.e.
- By use of a so called frac string with frac packer isolating the main well bore casing from the hydraulic fracturing pressures to prevent damage to main bore casing zonal isolation capabilities,
- Or through a mono bore cemented completion where by the main well bore casing is used as the conduit for placing the hydraulic fracturing fluids exposing the main bore casing zonal isolation capabilities to the potential ballooning of the casing and damage the cement sealing or isolation capabilities.
Other risk to be managed is the channeling of hydraulic fracturing fluids behind pipe or casing in to next annuli or overlying reservoirs or aquifers causing pollution to the environment or trapping high fracturing pressures behind casing that may cause casing collapse when producing the well.
Hydraulic fracturing and zonal isolation requirements need to be carefully planned and risk associated with each solution to be fully assessed with a confirmation of zonal isolation at completion of the hydraulic fracturing activity.
Well suspension is synonymous to temporary abandonment in many operating areas and is used to temporarily secure a well with cement plugs or other mechanical barriers in such a manner that ensures all fluids, hydrocarbons and water, are confined to their original indigenous strata for a temporary amount of time. The purpose of suspending a well is to reserve a wellbore and production equipment for future use. A suspended well must have appropriately placed and tested cement or mechanical plug barriers per local regulations that require periodic barrier inspections. Depending on local regulations there is a finite amount of time a well can be suspended before it must be plugged and abandoned.
Plug and abandonment
When there is no future economic use of a well (e.g. anon repairable well integrity issue, as necessary by regulations, or other reasons) the well'slast stage within the lifecycle is plug and abandonment (P&A).
P&A is process of permanently securing the well with cement plugs or other mechanical barriers in such a manner that ensures all fluids, hydrocarbons and water, are confined to their original indigenous strata.
Abandonment plugs should extend across all strings of tubing and casing annuli to seal horizontally as well as vertically through the full cross section of the wellbore. The purpose of the plugs is prevent any cross flow of fluids between fluid baring strata; as well as, prevent any fluid breaches at surface. The plugs in a well must also effectively segregate uncased and cased portions of the wellbore to prevent vertical movement of fluid within the wellbore. Some operating areas require removal of the tubing and portions of the casing prior to setting mechanical plugs or pumping cement plugs. The number, location, and length of the cement or mechanical plugs and the subsequent barrier verification tests required to P&A a well will vary by operating area regulations. After downhole and surface plugs are set the well head equipment and casing will be removed to a specified depth below ground level or mud line. After which an abandonment marker plate will be installed as specified by area requirements.
- D-010:2013. Well integrity in drilling and well operations. 2013. Lysaker, Norway: NORSOK. https://www.standard.no/en/sectors/energi-og-klima/petroleum/norsok-standard-categories/d-drilling/d-0104/
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
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
SPE. Well Integrity Technical Section. http://connect.spe.org/WellIntegrity/home.
Federico Juarez - Well Integrity Engineer
MJ Loveland - Well Integrity Supervisor ConocoPhillips