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We are happy provide a free copy of any of the papers listed below to qualified individuals. First select the paper(s) which you are interested in receiving. Then tell us about yourself, where we can reach you and what mailing address we can send the papers to. Alternatively you can purchase the papers directly from the Society of Petroleum Engineers at spe.org. |
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SPE
35214 - Euler Loads and Buckling
SPE 35214
Euler Loads and Measured Sucker Rod / Sinkerbar
Buckling
Scott W. Long, P.E., SPE and Donald W. Bennett,
SPE, Flexbar, Inc.
Copyright 1996, Society of Petroleum Engineers.
This paper was prepared for presentation at
the Permian Basin Oil & Gas Recovery Conference held in Midland, TX
27-29 March 1996.
Abstract
The Petroleum Industry is experiencing an increased awareness and understanding
of sucker rod compression. This awareness has evolved during the past
twelve years, from initial recognition of rod buckling, to a current desire
to quantify (measure) the amount of compression required to initiate rod
buckling.
Recent attention has focused on true or effective compressive loads in
sucker rod strings. Measurements of these loads is being documented (1)
and data collection is ongoing with improved technology.
This paper will provide a more accurate understanding of the amount of
compression required to buckle sucker rods and sinkerbars of various diameters.
This will be accomplished by presenting the following;
1. Predictive compressive loads that buckle various diameters and lengths
of sucker rods and sinkerbars utilizing Euler loads.
2. Measured compressive loads that are required to buckle various diameter
sucker rods and sinkerbars.
3. A comparison of predictive compressive loads to measured compressive
loads.
Knowledge regarding the amount of rod string compression required to
buckle various diameters sucker rods will provide the industry better
rod string design guidelines.
Use of these guidelines will help identify dangerous compressive rod
string loads which initiate rod-tubing contact, provide associated wear,
and result in rod and/or tubing failure.
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SPE
37502 - Wear and Side Loading
SPE 37502
Measured Rodstring/Tubing Wear and Associated
Side Loading
Scott W. Long, P.E., SPE and Donald W. Bennett,
SPE, Flexbar, Inc.
Copyright 1996, Society of Petroleum Engineers.
This paper was prepared for presentation at
the 1997 SPE Production Operations Symposium, held in Oklahoma City, Oklahoma,
9-11 March 1997.
Abstract
Ever since the first installation of steel sucker rods in production tubing,
the Petroleum Industry has been aware of rod sting and tubing wear. The
associated rod string and tubing wear with this artificial lift system
continues to have an impact on the ability to economically produce oil
and gas.
The downstroke phenomenon of sucker rod string compression, buckling,
sucker rod/tubing contact and associated sucker rod/tubing wear is becoming
more clearly defined (see References 1, 2, and 3) throughout the petroleum
industry.
This paper will provide the Petroleum Industry with a more accurate understanding
of sucker rod and tubing wear resulting from sucker rod side loading initiated
by downstroke sucker rod buckling. This paper will present a description
of test equipment and test parameters resulting in the following:
- Calculated cycles to 100% tubing wall loss vs. side loading.
- Calculated cycles to 100% sucker rod diameter loss vs. side loading.
- Calculated cycles to 100% sinkerbar diameter loss vs. side loading.
A better understanding of sucker rod and tubing wear will provide the
Industry with better sucker rod string design guidelines. Use of these
guidelines can reduce costly sucker rod and tubing wear and failures that
impact the ability of the Petroleum Industry to economically produce oil
and gas.
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SPE
67270 - PSU Best Practices
SPE 67270
Best Practices in the Preston Spraberry Unit
Scott W. Long, P.E., Flexbar, Inc., and
Elton J. Smith, Charlie R. Hoff, SPE and Albert Garza, Pioneer Natural
Resources USA, Inc.
Copyright 2001, Society of Petroleum Engineers
Inc.
This paper was prepared for presentation at
the SPE Production and Operations Symposium held in Oklahoma City, Oklahoma,
24-27 March 2001.
Abstract
During the last several years the Petroleum Industry had adopted the term
"Best Practices" to describe an efficient method of producing
oil and gas. The definition of this "method" is very subjective
and is continually changing with acceptance of new improved and proven
rod pumping knowledge. The best way to describe the term Best Practices
is by using the phrase "Work in Progress" or "Continuous
Improvement."
This paper describes and presents the implementation of a Best Practices
program in the Preston Spraberry Unit located in West Texas. This accepted
Best Practices program is presented as follows:
- Complete initial pumping well analysis.
- Matching lift operations to current producing rates by optimizing
the following: plunger diameter, stokes per minute, stoke length, tubing
anchor catcher, and downhole gas separation.
- Managing downhole rodstring buckling by re-evaluation of rodstring
designs and installation of sinkerbars.
- Installing pump-off controllers to manage production rates, optimize
run times and monitor equipment performance.
- Follow-up well-site diagnostic analyses after several months of operation
to evaluate initial well analysis and original well work, and implement
further modifications.
Due to the successful implementation of this Best Practices program,
tubing leaks were reduced by 61%, rod part replacements were reduced by
35%, and pump repairs were reduced by 6% during the two-year test period.
Recognition and continued development of these successful Best Practices
will provide the oil and gas industry with improved artificial lift guidelines
for more effective use of all valuable resources to more efficiently produce
oil and gas.
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SPE
67274 - Downstroke Friction
SPE 67274
Total Downstroke Friction From Downhole Dynamometer
Analysis
Scott W. Long, P.E., Flexbar, Inc., Elton
J. Smith, Kirk Mehaffey, and Albert S. Garza, Pioneer Natural Resources
USA, Inc.
Copyright 2001, Society of Petroleum Engineers
Inc.
This paper was prepared for presentation at
the SPE Production and Operations Symposium held in Oklahoma City, Oklahoma,
24-27 March 2001.
Abstract
The oil and gas industry is benefiting from development and use of improved
predictive computer programs that now utilize several friction defaults.
These predictive programs are more capable of predicting surface and
downhole rod pumping conditions. The need for improved predictive accuracy
is requiring program users to adopt improved estimates of downstroke friction
to model downhole pumping conditions. Lack of improved estimates of downstroke
friction has resulting in program users accepting and designing with current
friction defaults. Use of these defaults may culminate with results not
representative of actual downhole pumping conditions.
This paper develops a method of estimating total downstroke friction
from existing dynamometer analysis. Use of this method in producing fields
with similar operating conditions will provide improved estimates of total
downstroke friction.
A better understanding of the magnitude of total downstroke friction
will result in more effective designs of rodstrings and artificial lift
systems.
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2.8
Years of Polybar Performance
2.8 Years of Field Performance of High Density
Polyethylene Sleeved Sinkerbars (Polybars)
Scott W. Long, Flexbar, Inc.
Don Dillingham and James M. Northcutt, Occidental Permian, Ltd.
James Franklin, BP
Albert Garza, Pioneer Natural Resources, Inc.
Ed Gibson and David Snapp, Chevron, USA
Abstract
During the past 18 years, rodstrings installed with a properly designed
Sinkerbar Section have proven to reduce downstroke buckling and maintain
tension in all rods. Results from use of these rodstring designs have
been reduced rod-on-tubing wear and extended tubing and rod life.
During the past 5 years, use of high-density polyethylene liners in oilfield
tubing has shown to increase wear resistance and reduce the coefficient
of friction. Results from use of these liners in tubing have been reduced
rod-on-tubing wear and extended tubing life.
These successful oil field products and their benefits have been combined
to develop a high-density polyethylene sleeved Sinkerbar called a Polybar.
During this test, these Polybars exhibited the resistance to buckling
of a Sinkerbar with the wear resistance and coefficient of friction of
polyethylene.
This paper presents results of a 2.8 year field test involving five (5)-producing
wells installed with Polybars. The documented results show that no tubing
leaks occurred in tubing protected by Polybars.
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Sinkerbar
Comparative Analysis
Comparative Analysis
Scott W. Long, P.E., SPE and Donald W. Bennett,
SPE, Flexbar, Inc.
This analysis is based on an actual application installed by a major
oil company in February 1988. Actual data gathered substantiates these
predictives.
| |
ALL STEEL |
GLASS/
STEEL |
GLASS/
SINKERBAR |
| Design |
| Sucker Rod String
Design |
API 87 |
1.25" glass
1" steel rod |
1.25" glass
1.625" sinker |
| Percent Taper |
36%/64% |
60%/40% |
79%/21% |
| Constant Factors
- identical numbers were used for Depth, Pumping Unit, Prime Mover,
Stroke Length, Pumping Speed, Pump Size, and Pump Intake Pressure. |
| Production |
| Production (BBL/day) |
916 |
963 |
1110 |
| Increase |
--- |
5.1% |
21.2% |
| Efficiency |
| Power Required (HP) |
70.3 |
72.3 |
78.0 |
| Efficiency (BBL/HP) |
13.03 |
13.32 |
14.231 |
| Increase |
--- |
2.2% |
9.2%
|
| Rod Loading |
| Unit Torque (in balance-x1000 in./lbs.) |
630.5 |
594.9 |
602.0 |
| Percent of Rating |
98.5% |
93.0% |
94.1% |
| Peak Polish Rod Load |
25,938 |
22,387 |
22,979 |
| Min. Polish Rod Load |
4,322 |
2,837 |
3,324 |
| Rod Loading (%) |
* 104% |
91% |
89% |
| Buoyant Rod Weight |
10,404 |
7,262 |
9,179 |
* Class D Rods @ 1.0 Service Factor
Conclusions
Fiberglass/Sinkerbar Design VS API Steel
Design
| Efficiency |
9.2% Increase |
| Production |
21.2% Increase |
| Rod Loading |
14.4% Decrease |
Fiberglass/Sinkerbar Design VS Fiberglass/Steel Rod Design
| Efficiency |
9.1% Increase |
| Production |
13.2% Increase |
| Rod Loading |
2.2% Decrease |
Flexbar Sinkerbars and fiberglass sucker rods can produce
more fluid more efficiently in many cases. Let us help you design a better
rod string today!
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Other Technical Papers
SPE 22787
Design and Diagnosis of Deviated Rod-Pumped
Wells
S.G. Gibbs, SPE, Nabla Corp.
Copyright 1992, Society of Petroleum Engineers.
This paper was first presented at the 1991 SPE
Annual Technical Conference and Exhibition held in Dallas, Oct. 6-9.
Summary
A wave equation method is presented for the design of deviated rod-pumped
wells. Applications made to wells involve bare rods, molded-on guides,
and wheel-rod guides. The design method is also used to explain the types
of errors that result when vertical-hole techniques are used to compute
downhole pump cards in crooked wells.
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Sandia Report
SAND97-1652
Finite Element Analysis of Sucker Rod Couplings
with Guidelines for Improving Fatigue Life
Edward L. Hoffman
Prepared by
Sandia National Laboratories
Albuquerque, New Mexico 87185 and Livermore, California 94550
Sandia is a multiprogram laboratory operated by Sandia
Corporation, a Lockheed Martin Company, for the United States Department
of Energy under Contract DE-AC04-94AL85000.
Approved for public release; distribution is unlimited.
Abstract
The response of a variety of sucker rod coupling to an applied axial load
was simulated using axisymmetric finite element models. The calculations
investigated three sucker rod sizes and various combinations of the slimhole,
Spiralock, and Flexbar modifications to the coupling. In addition, the
effect of various make-ups (assembly tightness) on the performance of
coupling was investigated.
The make-up process, based on measured circumferential displacement of
the coupling from a hand-tight position, was simulated by including a
section of an axially expanding material in the box section which, when
heated, produced the desired mechanical interference which would result
from making-up the coupling. An axial load was applied to the sucker rod
ranging from -5 ksi to 40 ksi, encompassing three load cycles identified
on a modified Goodman diagram as acceptable for indefinite service life
of the sucker rods.
The simulations of the various coupling geometries and make-ups were
evaluated with respect to how well they accomplished the two primary objectives
of preloading threaded couplings: (1) to lock the threaded coupling together
so that it will not loosen and eventually uncouple, and (2) to improve
the fatigue resistance of the threaded connection by reducing the stress
amplitude in the coupling when subjected to cyclic loading. A coupling
will remain locked as long as the mating surfaces of the pin and box sections
remain in compression, resisting rotational motion of loosening.
The fatigue evaluation was accomplished in two parts: nominally and locally.
In the nominal evaluation, a set of equations based on the gross dimensions
of the coupling were derived which describe how a load applied to a sicker
rod is distributed throughout a preloaded coupling. The local fatigue
evaluation characterized the fatigue element simulations and a stress
equivalencing criterion for multiaxial stress states. The criterion is
based on Sines' equivalent stress theory which states that the permissible
effective alternating stress is a linear function of the mean hydrostatic
stress.
Perhaps the most significant finding in this study was the characterization
of the coupling parameters which affect these two stress measures. The
mean hydrostatic stress, which determines the permissible effective alternating
stress, is a function of the coupling make-up. Whereas, the alternating
effective stress is a function of the relative stiffnesses of the pin
and box sections of the coupling and, as long as the coupling does not
separate, is unaffected by the amount of circumferential displacement
applied during make-up.
The results of this study suggest approaches for improving the fatigue
resistance of sucker rod couplings.
Conclusions and Recommendations (excerpt)
Decrease the severity of the stress concentrations which provide preferred
sites for fatigue damage. This approach was taken in designing the Flexbar modification to the standard API coupling. The results of the Flexbar simulations indicate that this modification was successful in
reducing both the mean hydrostatic and effective alternating stresses
in the pin neck, extending the service life of the coupling with respect
to failure at this location.
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