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8th Annual Sucker Rod Pumping Workshop
Renaissance HotelOklahoma City, Oklahoma September 25 - 28, 2012
History of Slim Hole Coupling Derating Factors &
Application to Special High Strength Rods
by
Norman W. Hein, Jr., P.E.NPS – Norris/AOT
09/25-28/2012 2012 Sucker Rod Pumping Workshop 2
Content• Origin of Derating Factors by Mr. F. W. Gipson• Modifications by Mr. D. Hermanson• Extension of D Grade Rod Strength to Special
High Strength Rods• Conclusions and Recommendations
Gipson & Swaim – Green Book
• The first discussion that provides derating factors for slim hole couplings was published in the 1969 by Gipson & Swaim in the Conoco Green Book
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Green Book (first published 1969)• Although not discussed was why the derating was
required other than field failures were occurring.• Looking back into the production time of the
fields, it is assumed that waterflood response was occurring, wells were able to produce more fluids, and prior rod string installations were inadequate to handle the required, applied loads/stresses.
• Normally, if higher loads were being applied, rod body cross sectional area would still be the weak link and the body should fail first.
• This may be occurring again w/new, deeper wells09/25-28/2012 2012 Sucker Rod Pumping Workshop 5
Development of Derating Factors –T Class Couplings
• Gipson first compared full sized cross sectional area to associated rod body area.
• Established the following area relationship:
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Nominal Coupling Size (in)
(OD area)2
-ID area)2
(in)2
Rod Body Area(in)2
(Delta Coupling
Area)/ Rod Area
5/8 1.0508 0.307 3.42283/4 1.1579 0.442 2.61977/8 1.4398 0.601 2.39571 2.2342 0.785 2.8461
1- 1/8 2.4694 0.994 2.4843
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• Based on rod body to coupling areas, with the coupling area 2.4 to 3.4 times associated rod body area, the rod body is the weakest link.
• If couplings are properly made up to required connection preload, and then installation properly operated, you should “never” see a connection or coupling failure
Derating (cont)
Slim Hole Coupling Area Comparison
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• Similar coupling to rod area comparison made.• A derating of the slim hole (SH) coupling could
be made for all sizes but response from the field said 1” SH couplings were not failing.
• The derating was modified to normalize the factors to account for the non-failures of 1”SH couplings
Normalized SH Coupling Deratings
Nominal Coupling Size (in)
Delta Coupling Area (in)2
(Delta Area)/ Rod Body Area
Normalized Derating (prior column)/2.0606
½ 0.3234 1.6471 0.79935/8 0.5109 1.6642 0.807¾ 0.8510 1.9253 0.93437/8 0.9337 1.5536 0.75401 1.6176 2.0606 1.000
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Rod Strength vs. Coupling Strength
Rod Grade Tensile Range (ksi)
Coupling Tensile (ksi)
C &K 90 to 115 90 minAll 3 D 115 to 140 (56 to 62 HRa)
Special HS 140 to 150 (155; 160)
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Dean Hermanson’s Extension
API Rod Size (in) Normalized Derating Factor5/8 0.81¾ 0.937/8 0.751 1.0
API Rod Size (in)
API Grade K API Grade C API Grade D
5/8 na 0.97 0.77¾ na na 0.867/8 0.93 0.88 0.691 na na 0.89
Special High Strength Rod – T Class Derating Extension for SH & FS
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Conclusions
• Gipson’s mathematical comparison of areas originally resolved connections failing; but this compared nominal C versus coupling T grade.
• Hermanson said that if D grade rod used versus T grade couplings, then SH deratings may need to be further reduced.
• Extending strength comparison to special HS rods says deratings need further reduction not only for SH, but also FS.
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• Rod string designs need to consider the potential need to apply the SH derating factor or at least provide to the operator that a failure potential may exist
• If don’t want or can’t derate rod string, then operator needs to run the correct sized tubing in the length requiring SH couplings
• This can be run as full length or tapered tubing string
• Or could consider running special HS couplings09/25-28/2012 2012 Sucker Rod Pumping Workshop 14
Recommendations
Precaution
• Many rod strings have been installed w/o excessive failures even though SH couplings included
• Some believe there is not a need to derate; but there has been recent rash of coupling failures high in the string
• Operators may want to consider running a “pilot” string w SH couplings w/o derating to see if there are operational problems/failures then take the risk
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09/25-28/2012 2012 Sucker Rod Pumping Workshop
CopyrightRights to this presentation are owned by the company(ies) and/orauthor(s) listed on the title page. By submitting this presentation to the Gas Well Deliquification Workshop, they grant to the Workshop, the Artificial Lift Research and Development Council (ALRDC), and the Southwestern Petroleum Short Course (SWPSC), rights to:
– Display the presentation at the Workshop.– Place it on the www.alrdc.com web site, with access to the site to be
as directed by the Workshop Steering Committee.– Place it on a CD for distribution and/or sale as directed by the
Workshop Steering Committee.Other uses of this presentation are prohibited without the expressed written permission of the company(ies) and/or author(s) who own it and the Workshop Steering Committee.
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09/25-28/2012 2012 Sucker Rod Pumping Workshop
DisclaimerThe following disclaimer shall be included as the last page of a Technical Presentation or Continuing Education Course. A similar disclaimer is included on the front page of the Gas Well Deliquification Web Site.The Artificial Lift Research and Development Council and its officers and trustees, and the Gas Well Deliquification Workshop Steering Committee members, and their supporting organizations and companies (here-in-after referred to as the Sponsoring Organizations), and the author(s) of this Technical Presentation or Continuing Education Training Course and their company(ies), provide this presentation and/or training material at the Gas Well Deliquification Workshop "as is" without any warranty of any kind, express or implied, as to the accuracy of the information or the products or services referred to by any presenter (in so far as such warranties may be excluded under any relevant law) and these members and their companies will not be liable for unlawful actions and any losses or damage that may result from use of any presentation as a consequence of any inaccuracies in, or any omission from, the information which therein may be contained.The views, opinions, and conclusions expressed in these presentations and/or training materials are those of the author and not necessarily those of the Sponsoring Organizations. The author is solely responsible for the content of the materials.The Sponsoring Organizations cannot and do not warrant the accuracy of these documents beyond the source documents, although we do make every attempt to work from authoritative sources. The Sponsoring Organizations provide these presentations and/or training materials as a service. The Sponsoring Organizations make no representations or warranties, express or implied, with respect to the presentations and/or training materials, or any part thereof, including any warrantees of title, non-infringement of copyright or patent rights of others, merchantability, or fitness or suitability for any purpose.
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