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Well integrity thermal
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.
Wells that are used for steam injection or steam soak production or Geothermal heat are subject to high differences in thermal cycling and also referred to as Thermal wells. Thermal wells have specific well integrity issues or risk from the stresses and strains in a cemented casing that are incurred during steaming or thermal operations.
Most steaming or thermal operation will result in casing stresses exceeding yield so a conventional elastic load based well design is not possible. Steam injection or Geothermal production induces high temperatures, while shutting in a well can result in temperatures returning to close to the overburden temperature. These temperature extremes will cause most casing strings to yield in compression when hot and then when cooled it may yield in tension.
To manage well integrity effectively one would have to assess the effect of the number of temperature cycles that are likely to occur in a thermal well from planned cyclic operations , production , injection and periods of shutdowns to be able to model the fatigue life of the tubing and casing subject to the number of cycles, high temperature changes often operates just above the yield strength of the material and cycles forth and back in the elastic deformation window of the steel in use area that can be modeled, several operating companies have developed their own models for this that determine the safe number of cycles before work over or abandonment should take place.
It should be noted that stresses from 80 degrees Celsius versus 130 degree Celsius are a magnitude larger adding a corrosive environment may lead to corrosive stress cracking of materials, corrosive stress cracking has been seen on components like tubing hangers and wellhead connectors or flanges as a result of high temperatures and chloride of residual brines trapped in cavities of wellhead or annuli, it is key to flush these when completing the well with potable water to eliminate this risk.
The corrosive element of thermal wells metallurgic oilfield materials handbook and pipe manufacturers refer to heat under certain conditions forming a protective layer of oxidation on the pipe wall that provides a natural corrosive protection film when not disturbed and works in linear flow paths lesser in turbulent or erosive flow areas.
It should be noted that when injecting steam in to a reservoir and being produced back often changes are experienced in the composition of effluents, sweet fields may turn sour and produce H2S and CO2 as result of steam injection when designing for life cycle integrity this should be considered in the design stage of the well.
Due to cyclic behavior and pipe working exceeding hoop stress cement bonds often reduce over life cycle that need to be considered for zonal isolation risk and at end of well life with respect to restoring isolation for well abandonment.
The use of heat saver tubing and gas blanketing on annuli will reduce the thermal affects over the life cycle of the well and also will reduce heat loss that will extend the well life or number of thermal cycles the well can handle.
- 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