8th Annual Sucker Rod Pumping Workshop
Renaissance HotelOklahoma City, OklahomaSeptember 25 - 28, 2012
Recording Dynagraph on Bent / Misaligned Polished rod.
Avinav Kumar, Atul D PatilOil and Natural Gas Corporation ( ONGC ) , India
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Introduction Dynamometer card used for years to establish and
optimize rod pump system efficiency.
Proper analysis of dynamometer important to ascertain
surface and sub-surface pumping problems.
Predominantly used dynamometer Polished rod
transducer ( PRT ) and Horse shoe load cell.
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Introduction Both PRT and Horse shoe load cell records load at the
polished rod ( plotted along Y axis ) as a function of
polished rod displacement ( plotted along X axis ).
An ideal surface & sub-surface cards usually rectangular
in shape.
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Dynamometers Load Cell General three types of dynamometers used to acquire
dynamometer data :
Electronic dynamometers being used predominantly
Dynamometer
Mechanical Hydrualic Electronic
Polished Rod transducer
Horseshoe Load cell
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Polished Rod Transducer (PRT) PRT is attached 6” – 8” below the carrier bar .
Unit not stopped during installation . Position of plunger
in the pump barrel not changed during installation.
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PRT measures change in diameter / elongation in polished
rod due to stress in axial direction and converts
corresponding strain to change in load on polished rod .
Polished Rod Transducer (PRT)
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Load measurement
Radial Strain (Ɛ) = ( δ d )/D
Axial Strain ()= Radial Strain () / Poisson’s Ratio ()
Axial Stress = Polished rod load (PRL) / cross sectional
area (A) = Axial Strain (Ɛ ) * Young's modulus ( E )
PRL = [(δ d ) /( D)*E *A]/ ()
Position measurement : using accelerometer
Load at various position plotted against position to
generate surface and sub-surface dyna cards.
Polished Rod Transducer (PRT)
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Bent Polished rod will not have
uniform change in diameter at all
the points along the rod diameter
at particular distance from carrier
bar.
At point A and B diameter
change not uniform.
Dyna cards shapes different at
point A and B.
Polished Rod Transducer (PRT)
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Dyna cards shapes different at point A and B. Sloped
/aberrantly shaped.
Polished Rod Transducer (PRT)
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Polished Rod Transducer (PRT)
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Inherent bent in polished rod not visible to naked eye.
Bent induced in the polished rod :
Misaligned carrier bar.
Unit not centered properly.
Unit too far forward / back .
Polished Rod Transducer (PRT)
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Misaligned carrier bar
Polished Rod Transducer (PRT)
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Unit not centered properly
Polished Rod Transducer (PRT)
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Unit too ahead or back
Polished Rod Transducer (PRT)
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Horse Shoe Load Cell Horse shoe load cell is
attached between
pumping unit carrier bar
and polished rod clamp.
Unit stopped during
installation. Position of
plunger in the pump
barrel changed during
installation.
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Measures the load directly, unknown or inaccurate
physical properties of polished rod have no influence
Horse Shoe Load Cell
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PRT vs. Horse shoe load cell
Polished Rod
TransducerHorse shoe Load cell
Load
measurement
Converts strain to load on the
polished rod during the stroke.
Horse shoe load cell measures the
load directly
Installation
Installed 6‐8” below carrier bar .
Unit not stopped during
installation
Between clamp and carrier bar. Unit
stopped for installation
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PRT vs. Horse shoe load cell
Polished Rod
TransducerHorse shoe Load cell
Plunger
position
Position of plunger in pump is
not changed
Position of plunger in pump
changed during horse shoe
installation
Bent /
misaligned
polished rod
Inherent bent in polished rod or
misaligned polished rod affects
recording of load by PRT
Hose shoe load cell measures load
directly
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Case Studies – Well ACompletion details: Production Details
Tubing 2 7/8” Liquid (bbls/day) 80
Pump depth /
diameter1000 mts / 2.25” Water cut 90%
SRP unit API – 160D-173-86” Oil rate (bbls/day) 8
Pump operating Parameters Echo meter results
Stroke length 71.4” Static liquid level NA
SPM 2.2Dynamic liquid
levelNA
Envisaged production at 100% pump efficiency = 90 bbl./day.
Actual production = 80 bbl./day
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Case Studies – Well AWith Polished Rod Transducer
Fig 1 Fig 2
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Case Studies – Well AWith Polished Rod Transducer
Fig 3 Fig 4
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Case Studies – Well AWith Horse shoe load cell
Fig 5
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Case Studies – Well AProduction Parameters :
Stroke length : 74” ; Production : 85 bbl./day
Figure Load Cell used
Surface Stroke Length
Subsurface Stroke Length PPRL (lbs.) MPRL
(lbs.)
Pump displacement
(bbls/day) from Dynacard
Fig 1 PRT 71.4” 102” 7701 846 131.3
Fig 2 PRT 71.4 78.0” 7586 5433 48.8
Fig 3 PRT 71.4” 89.9” 6349 2769 116.1
Fig 4 PRT 71.4” 65.9” 11194 4792 32.6
Fig 5Horse
Shoe71.4” 72.1” 6256 5242 92.9
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Case Studies – Well APumping unit not centred properly :
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Case Studies – Well APolished Rod not straight :
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Case Studies – Well BCompletion details: Production Details
Tubing 2 7/8” Liquid (bbls/day) 120
Pump depth /
diameter1000 mts / 2.25” Water cut 80%
SRP unit C-228-213-100 Oil rate (bbls/day) 24
Pump operating Parameters Echo meter results
Stroke length 71.3” Static liquid level NA
SPM 3.7Dynamic liquid
level75 mts
Envisaged production at 100% pump efficiency = 135 bbl./day.
Actual production = 120 bbl./day
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Case Studies – Well BWith Polished Rod Transducer
Fig 6 Fig 7
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Case Studies – Well BWith Polished Rod Transducer
Fig 8
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Case Studies – Well BProduction Parameters : Stroke length : 74” ; Production : 120 bbl./day
FigureLoad Cell
used
Surface
Stroke
Length
Subsurface
Stroke
Length
PPRL
(lbs.)MPRL (lbs.)
Pump displacement
(bbls/day) from
Dynacard
Fig 6 PRT 71.3” 69.4” 9906 5990147.9
Fig 7 PRT 71.3” 64.7” 9650 648287.0
Fig 8 PRT 71.3” 70.6” 8850 5648 151.9
Horse shoe load cell could not be used due to unavoidable reason
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Case Studies – Well BUnit too back :
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Conclusion
Though Polished rod transducer is quick and easy to install, it
may not represent actual pump action every time.
Any inherent bent or bent induced in polished rod will affect
load recording by PRT.
Horseshoe measures load directly, any inherent bent or any
induced bent will have no effect on recording of load.
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Sept. 25 - 28, 2012 2012 Sucker Rod Pumping Workshop 33
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