Coiled Tubing in Sour Environment -Theory and Practice
- Alexander R. Crabtree (BJ Services Co.) | William Gavin (BJ Services Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2005
- Document Type
- Journal Paper
- 71 - 80
- 2005. Society of Petroleum Engineers
- 3.2.4 Acidising, 1.7.1 Underbalanced Drilling, 2 Well Completion, 4.2.3 Materials and Corrosion, 5.3.2 Multiphase Flow, 3.1.6 Gas Lift, 1.6 Drilling Operations, 3 Production and Well Operations, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing)
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Carbon steel CT (CT) strings have been used in sour wellbore environmentsfor many years. The use of CT in sour service has increased by job number, jobcomplexity, pipe size, and the stresses to which the pipe is subjected. Anumber of papers have been written on the steel chemistry and low-cycle fatiguebehavior. These papers have been based on both theoretical and laboratory work.Great progress has been made in understanding the chemical and physicalinteraction of CT and H2S, but little information is available from"real-world" situations in which the pipe has been worked in a variety of jobtypes (e.g., acidizing, gas lifting, and drilling) and in which a large numberof other factors may come into play (e.g., injector damage, well-stimulationchemicals, sour inhibitor application techniques, erosion of inhibitors, CO2,and high-chloride water production).
This paper discusses the application of a CT technical specification (basedon theoretical and laboratory work) in the operational world. Comparisons willbe made between theoretical expectation and practical observation for 70- and80-grade CTs with regard to low-cycle fatigue, pipe life, and damage in sourenvironments.
CT has been used successfully for more than 20 years in sour wellenvironments in Canada and elsewhere.The nature of the wells, however,has changed, which, in turn, has changed the demands placed uponCT.Accessing sour wells under live conditions, to perform the usual rangeof interventions offered by CT, is an increasing requirement. To meet theserequirement changes, the CT manufacturers—for their part—have responded byoffering a greater range of yield strengths, diameters, and wallthicknesses.
Coincident with these changes to CT have been changes in the requirementsplaced upon the industry in Canada by the regulatory authorities. Parts ofthese requirements are outlined by MacArthur et al.1
The Alberta Energy and Utilities Board (AEUB) began to extend the conceptsnoted in the above paper when considering approvals for the underbalanceddrilling of critical sour wells.Work was jointly undertaken by severalindustry experts to develop an industry recommended practice (IRP) under theauspices of the Drilling and Completions Committee (DACC).Part of thedifficulty with developing the IRP with respect to CT is that the material isused in such a way that continually subjects it to plastic-strainreversals. This type of mechanical-strain situation is not examined bythe Natl. Assn. of Corrosion Engineers (NACE) when preparing its list ofrecommended materials for sour serviceability.2These issues are discussedby H.B. Luft and G. Wilde.3
Additionally, sour-environment testing of CT by use of the bent-beammethodology, as specified by NACE Standard TMO177-96,4 was performed by a JointIndustry Project (JIP) on several grades of CT,5 as well as low-cycle fatigueof samples exposed to a sour environment.Part of the outcome of the JIP'stesting would suggest that there is no difference in susceptibility to a sourenvironment for the differing grades of CT, but all are equally affected whensubsequently subjected to low-cycle fatigue.
Further testing work continued to determine the suitability of CT for use incritical sour underbalanced drilling for the IRP, and under what operatingconditions.6
These previous bodies of work can not be directly translated for use ingeneral workover applications because the work contained in both the JIP studyand in paper SPE 81723 relates specifically to CT that is exposed for extendedperiods, solely to sour environments.
However, some information was extracted out of the testing that had beenperformed to help formulate a purchase specification for CT that would be usedin general workover well interventions.
This paper presents a review of how strings of CT used in interventions haveperformed after the introduction of the purchase specification and how acomplete string-management system has been developed. It should be noted thatnone of the strings specified have been used in drilling critical sour wellsbecause there is a moratorium on this activity. The data presented, and the CTstrings reviewed, are from a single service company.
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1. MacArthur, J. et al.: "Coiled Tubing NDT Inspection:Implementation, Experience, and Results," paper SPE 56940 presented at the1999 Offshore Europe Oil and Gas Exhibition and Conference, Aberdeen, 7-10September.
2. "Standard Material Requirements—Sulfide Stress Cracking ResistantMetallic Materials for Oilfield Equipment," NACE Standard MR0175-2002, NACEIntl., Houston (2002).
3. Luft, H.B. and Wilde, G.: "Industry Guidelines for UnderbalancedCoiled-Tubing Drilling of Critical Sour Wells," paper SPE 54483 presentedat the 1999 SPE/ICoTA Coiled Tubing Roundtable, Houston, 25-26 May.
4. "Standard Test Method—Laboratory Testing of Metals for Resistance toSulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments,"NACE Standard TM0177-96, NACE Intl., Houston, (December 1996) 13.
5. "Serviceability of Coiled Tubing—Phase II," final report, InterCorrIntl., Houston (September 2002).
6. Luft, H.B.: "The Low CycleFatigue and Plastic Strain Response of CT in a Sour Environment With andWithout Corrosion-Inhibition Protection," paper SPE 81723 presented at the2003 SPE/ICoTA Coiled Tubing Conference and Exhibition, Houston, 8-9 April.
7. "Alberta's Reserves 2002 and Supply/Demand Outlook 2003-2012," AlbertaEnergy and Utilities Board, Statistical Series 2003-98, Calgary (2003) 4-8.
8. "Oil and Gas in British Columbia - Statistics and Resource Potential,"British Columbia Ministry of Energy and Mines, Victoria, British Columbia,Canada (2004) 4.
9. "Exports by U.S.Region" Natl. Energy Board, Calgary (2002)
10. Tipton, S.M. et al.: "Quantifying the Influence of Surface Defects on CTFatigue Resistance," paper SPE 74827 presented at the 2002 SPE/ICoTAConference, Houston, 9-10 April.
11. "Critical SourUnderbalanced Drilling," IRP, 6, .
12. Campbell, A.J.: "Coiled-Tubing Management System: AReview After Two Years in Operation," paper SPE 36339 presented at the 1996SPE/ICoTA North American Coiled Tubing Roundtable, Conroe, Texas, 26-28February.