Well Integrity Technical Section

The integrity management plan had been built around conventional oil and gas barrier philosophy - primarily focused on pressure containment, cement bond quality, and annular pressure monitoring. What it hadn't fully accounted for was the mechanical fatigue dimension: the casing experiencing hundreds of heat-up and cool-down cycles over the well life, each cycle ratcheting the deformation a little further.

We flagged these wells as integrity anomalies, but the harder question then became: what's the right remediation philosophy? Workover to run a patch? Accept and monitor with reduced operating envelope? Abandon and redrill? And how do you set defensible fitness-for-service thresholds when the standards (NORSOK D-010, ISO 16530) weren't written with thermal cycling mechanics specifically in mind?

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Kishore Maheshwari
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Kishore,

Thermal well integrity is an important subject area and has received significant attention and focus over many years, especially here in Alberta. I would suggest you plan to attend the annual SPE Thermal Well Integrity and Production Symposium in Banff at the end of November where many case histories are typically presented. The intermediate (production) casing and primary cement are main barriers and usually they retain sealing function even after many thermal cycles, even after appreciable casing deformation. If the casing ultimately fails, then a patch can be installed or a liner can be cemented in place for a more permanent repair. Degraded primary cement can lead to a surface casing vent flow, which triggers diagnostic investigation and repairs if needed. A wide variety of logging services are available for cement and casing evaluation.

Bill Plaxton

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Hello Kishore,

Thermal cycling of intermediate casing has been the topic of significant discussion in cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) wells in Alberta. I agree with Bill Plaxton's comment regarding the merit in attending the Thermal Well Integrity and Production Symposium: https://www.spe-events.org/symposium/thermal-well-integrity-and-production\

A few casing-related comments that I hope are helpful initial input to the questions you asked:

• The DACC IRP 3 (2012) document is a key reference: https://www.energysafetycanada.com/sites/default/files/2026-05/DACC%20IRP%203%20-%20In%20Situ%20Heavy%20Oil%20Operations%20-%20Sanctioned_0.pdf 
• There has been a considerable amount of work done on characterization of fundamental mechanical properties of materials that will contribute to the structural response of the cemented intermediate casing system under thermal cycling and other secondary loading. Specifically, elevated-temperature, slow-strain rate monotonic and cyclic properties contribute to both the axial load state in the casing system and the deformation-tolerance of the pipe body and sealability performance of premium connections. SPE papers that may contain useful information for you include SPE 97730-PA, SPE 97775-PA, SPE 105717-PA, and SPE 193363-MS.
• With respect to thermal cycles, response is highly path dependent given tubulars are generally operating beyond their yield point. For this reason, it is prudent to consider the magnitude of each thermal excursion for the integrity assessment. We proposed a classification system for thermal cycle severity in this 2019 paper: SPE 198682-MS, and would be interested in your feedback.
• On occasion, in our interpretations of multi-finger caliper data in thermal intermediate casing strings, we have seen extended regions with modest pipe ovality not related to geomechanical movements. A corresponding example analysis of pipe stability under external pressure in post-yield conditions is described in SPE 151810-PA. 
• With respect to connection integrity, the ISO/TS 12835:2022 analysis and full-scale testing protocol (originally labelled "TWCCEP" - thermal well casing connection evaluation protocol) emerged from an industry-sponsored Multi-Client Project and specifically focuses on structural and gas sealability evaluation through post-yield cycles to various Application Severity Levels as high as 350C. Test samples are subjected to ten thermomechanical cycles and then subjected to a limit-strain evaluation. This does not explicitly identify fatigue limits, but may provide a helpful starting point for complementary evaluations.
• H2S exposure is known to be synergistic with cyclic plasticity, and is not well-characterized by standard tests evaluating material suitability. Publicly-released findings of another industry project are available in NACE C2015-5988.   

Kind regards,

Dan

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Dan Dall'Acqua, P.Eng.
Principal Consultant
Noetic Engineering
ddallacqua@noetic.ca

Co-Chair, SPE WITS Casing Deformation Work Group
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