An image of a Surface Dynamometer Card as the well pumps off | Downhole Diagnostic

Dyno Survey

A Downhole Pump Card with incomplete pump fillage and pounding fluid | Downhole Diagnostic

If you want a concise summary of what a Dynamometer is and how it works, click HERE to go back to the Services Page.

Fluid Level Shots & Dynamometer Cards
 
Perfect 100% Fillage

Perfect 100% Fillage

Dynamometer Cards: perfect 100% pump fillage with anchored tubing (rectangular pump card).

Unanchored Tubing

Unanchored Tubing

Dynamometer Cards: 100% liquid fillage with unanchored tubing. Pump card slants up-right at the Rod Spring Constant.

Fluid Pound Cards

Fluid Pound Cards

Dynamometer Cards: well is fully pumped off to the SN and pounding fluid 45% fillage.

Gas Interference

Gas Interference

Dynamometer Cards: this well has a long-stroke pumping unit with bad gas interference with the stereotypical gas compression down-stroke.

Gas Interference w/ Gas Expansion

Gas Interference w/ Gas Expansion

Dynamometer Cards: gas interference/compression seen on the down-stroke and lots of gas expansion seen at the start of the up-stroke (which usually indicates a poor compression ratio in the pump; check the pump spacing).

Pump Tag - Overtravel

Pump Tag - Overtravel

Dynamometer Cards: pump has a solid down-stroke tag and the Pump Card shows lots of over-travel (downhole stroke length is much longer than the surface stroke length at the pumping unit).

Tagging - Tag vs No Tag

Tagging - Tag vs No Tag

Dynamometer Cards: the blue cards show the well tagging hard (lots of noise generated in the cards from the tag). I raised the rods to remove the tag and then cards smoothed out (black cards).

Pump Tag - 10K

Pump Tag - 10K

Dynamometer Cards: Pump had a very solid tag: 10,000-lbs of compression! This is how you smash the top clutch of the pump (shown in image).

Pump Tag - Slow Stack Out

Pump Tag - Slow Stack Out

Dynamometer Cards: pump has a solid tag but this unit is running at a slow SPM with a short stroke length and so the tag did not seem to hard at surface, but it is damaging and unnecessary. The rods stack out on the pump 8" before the bottom of the down-stroke. Considering how short the SL is, this 8" tag is consuming about a 1/3rd of the downhole stroke length!! Raising the rods will increase production by increasing the stroke at the pump.

Upstroke Pump Tag

Upstroke Pump Tag

Dynamometer Cards: the plunger is pulling into the top of the pump (trying to unseat it) at the top of the up-stroke. You know the pump is spaced far off bottom when you see this: need to drop the rods.

Pump Tag - Based on Fillage

Pump Tag - Based on Fillage

Dynamometer Cards: the pump is spaced very close to bottom and it does not tag when it has 100% fillage but it does tag when the fillage drops (due to the changing dynamics of the stress waves in the rod string); well has Fiberglass rods.

Worn Pump

Worn Pump

Dynamometer Cards: pump is worn but still has some life left.

Worn Pump - Worn Out

Worn Pump - Worn Out

Dynamometer Cards: the downhole rod pump is completely worn out and is close to picking up the full fluid load in the middle of the stroke but it never does. The well was not producing anything in this condition: need to change the pump.

Hole in Pump Barrel

Hole in Pump Barrel

Dynamometer Cards: the pump has a hole in the bottom third of the pump barrel and once the bottom of the plunger moves past the hole the pressure across the plunger is equalized and the fluid load on the plunger drops to zero. The image shows the pump barrel in the tubing and shows how this pressure equalization works.

Delayed Traveling Valve Closure

Delayed Traveling Valve Closure

Dynamometer Cards: the cards show normal 100% fillage cards versus two strokes with the pick-up in the fluid load is delayed. The Delayed Traveling Valve Closure is due to either trash getting between the ball and seat of the Traveling Valve or some damage damage on the surface of the Traveling Valve. (it can also be due to Bottom Discharge Valves not immediately seating if your pump has those installed).

Plunger Stuck in Pump Barrel

Plunger Stuck in Pump Barrel

Dynamometer Cards: pump plunger is stuck in the barrel and the whole up-stroke is nothing but rod tension.

Rods Sticking in Paraffin

Rods Sticking in Paraffin

Dynamometer Cards: the rods are sticking/balled up in paraffin and the plunger is still moving some but most of the stroke is lost due to rod stretch from the paraffin binding to the rods. The downhole pump is not computed correctly as the Wave Equation things the tension from the paraffin is actually some force acting downhole at the pump (...it does not know it is acting higher up the hole due to the paraffin friction).

Solids Grinding Between Plunger & Barrel

Solids Grinding Between Plunger & Barrel

Dynamometer Cards: Solids getting caught between the plunger and barrel and partially sticking the plunger for a second (tension is pulled which frees the plunger).

Friction Card

Friction Card

Dynamometer Cards: This is an example of some higher dog-leg (severe deviation in the wellbore) which is causing a lot of rod-on-tubing friction at that point. The pump is set at 10,000' on this well and the dog-leg is around 3500'. The Wave Equation does not know there is a localized point of excessive friction higher up the hole and thinks everything is happening at the pump, so the pump card is not properly computed (which causes the characteristic down-right slant of the Pump Card).

Leaking Standing Valve

Leaking Standing Valve

Dynamometer Cards: The Standing Valve is partially leaking and the full fluid load is only released off the plunger in the middle of the down-stroke when the plunger is moving the fastest.

Hydraulic Horsepower Card

Hydraulic Horsepower Card

Dynamometer Cards: This is an example of a shallow well with an over-sized tubing pump (2.75" in a 2-7/8" tubing). The pump is bottled-up and you see a hump at the start of the up-stroke due to the increased acceleration/friction forces from pushing so much fluid through the restricted ID of the tubing.

Stuffing Box Friction

Stuffing Box Friction

Dynamometer Cards: This is an example of excessive stuffing box friction distorting the card. The stuffing box friction is seen as the pumping unit changes directions and is highlighted by the brackets.

Slippage vs Gas Locked

Slippage vs Gas Locked

Dynamometer Cards: Example cards from the same well when it had 100% liquid fillage (with some slippage) versus when the pump gas locked. Look at the difference in area between the cards (which represent the amount of work being performed).

Combo - Rod Stretch + Tag

Combo - Rod Stretch + Tag

Dynamometer Cards: The well shows lots of rod stretch (due to a high fluid load from the 2" pump and a lot of stretchy fibgerglass rods) and it has a solid pump tag. Think you could feel the tag at surface??? The tag is arriving to surface 35" into the up-stroke, so it is not the easiest tag for the pumper to identify if they don't have some dynamometer cards to look at.

Changing SPM

Changing SPM

Dynamometer Cards: This well had a VSD (Variable Speed Drive) and the unit is increasing SPM from 4.5 to 8.2 during the cards shown. Notice how the downhole stroke length increases as the pump gets some over-travel due to the elasticity of the fiberglass rods being jerked around.

Can Opener Card

Can Opener Card

Dynamometer Cards: This is what is termed as a "Can-Opener" card and it is a combination of incomplete pump fillage (either due to gas interference or fluid pound) and wear/slippage.

Gas Pound - Fillage Slowly Dropping

Gas Pound - Fillage Slowly Dropping

Dynamometer Cards: The pump fillage is slowly working down each stroke in this data set. The cards tend to indicate fluid pound based on there shape but the Fluid Level Shot indicates there is 300' of Gas Free Liquid Above the Pump (GFLAP), so this is what I term "Gas Pound".

Traveling Valve Ball Damaged

Traveling Valve Ball Damaged

Dynamometer Cards: The cards on this well change from good 100% fillage cards to cards that show heavy wear. How can a pump change back and forth from being worn to not being worn? Answer: pitting or misshaped Traveling Valve ball. Depending how the ball lands from stroke-to-stroke affects how effectively the plunger/valve create a pressure seal on the up-stroke.

Tension at Polished Rod Box

Tension at Polished Rod Box

Dynamometer Cards: You might jump to the conclusion these cards show an up-stroke tag at the pump but notice how the tension at the pump is slanted up-right. In this well, the Polished Rod was not spaced properly and the coupling/box on the bottom of the PR was being pulled up into the stuffing box creating the tension. The software doesn't know that and assumes the tension is occurring at the pump.

More slide-shows like this can be found on the Oilfield Pictures Page!!

Example Dyno Card Videos

Click on the Screen-Shot image below, scroll left/right through the example Dyno Cards and then click the
"
Go to Link" (below the image title when the image is expanded) to see the video of the example Dyno cards.

Example Dyno Survey Reports (Echometer reports related to the Dyno Videos above):

       1.  Fluid Pound (Pumped Off)

       2.  Gas Interference

       3.  Gas Interference (Cycling Gas Int.)

       4.  Worn Pump

       5.  Tag on Pump

       6.  Unanchored Tubing (TAC Not Set)

       7.  Trash in Pump (Missing Strokes) - SV Not Closing

Page 2 of my Sucker Rod Pumping Short Course (see the Resources page to download).

Brochure summarizing the Principles of Sucker Rod Pumping including the dynamometer cards, pump card interpretation, and rod pumping optimization | Downhole Diagnostic
How a Dynamometer Works:

 

A Dynamometer is a diagnostic device used on Sucker Rod Pumped Wells that measures the load on the top rod (Polished Rod) and plots this load in relation to the polished rod position as the pumping unit moves through each stroke cycle.  The plot of the polished rod Load vs Position is known as the Surface Card.

 

The load on the polished rod is a summation of every load occurring downhole and is thus a function of:  the fluid load on the pump, the rod-string design and the buoyant rod weight, the acceleration forces (which are a function of the SPM x SL, pumping unit geometry and the direction of rotation), the mechanical friction of the rods-on-tubing (and the rods on paraffin, etc), and the viscous frictional forces generated between the rods and fluid.  With the Surface Card being affected by so many different factors, there is no "standardized" shape to Surface Cards—which greatly increases the difficulty of interpreting what is happening downhole.  For example, compare the shapes of the "flying duck" Surface Card (from an all steel string) at the top of the page with the Surface Card shown in the top left corner of the sheet above (50% Fiberglass rod string).

 

Although there is some value to be gather from the Surface Card, oil operators are much more interested to know what is happening downhole at the pump.  After all, the only reason for having any of the surface or downhole equipment is to effectively actuate the downhole pump so new fluid will be drawn into the tubing and lifted to surface.  

 

Thankfully, a very intelligent man by the name of Dr. Sam Gibbs [Lufkin's well known "Sam POC" was named in his honor] provided a solution to this problem when he developed the Wave Equation.  The Wave Equation models the elastic behavior of the rod string in its dynamic motion—which allows the surface measurements acquired from the polished rod to be “waved” downhole to the pump to generate a plot of the Load vs Position on the pump's plunger.  This plot is known as the downhole Pump Card.  The beauty of the Wave Equation is that it allows surface data to be acquired (which is easily accessible and inexpensive) and then mathematically filters the data to illustrate the downhole pump performance each stroke.  By filtering out the effects of the rod-string and everything else occurring above the pump's plunger, the Wave Equation essentially standardizes the various shapes the Pump Card can take and greatly improves the ability of the pump performance to be properly diagnosed. However, interpretation can still be difficult at times due to the simultaneous occurrence of multiples factors affecting the shape of the Pump Card.

 

The Wave Equation is also employed in Predictive Rod Design Programs, with the best known programs being RODSTAR (by Theta) & SRod (by Lufkin).  These programs give the rod designer a great deal of control and versatility in simulating various downhole conditions—allowing for the prediction of mechanical stresses on each rod taper and the expected producing performance of the pumping system.  These programs can be quite pricey.  For those who do not need to perform many complicated design simulations, it is worth noting that Echometer provides a completely free software that solves the Wave Equation—known as QRod.  Compared to other programs, QRod is much more simplified with fewer design controls, but the accuracy of its computations is comparable with the other two programs for vertical wellbores.  You can download QRod for free at www.echometer.com.

 

In addition to acquiring the Surface & Pump Cards over the well's pumping cycle, Dynamometers are also used to quantify the amount of Fluid Slippage leaking by the pump's plunger.  When both upper corners of the Pump Card are rounded-off Fluid Slippage is indicated—but the Pump Card in itself does not provide a means of determining how much slippage is occurring.  In order to quantify this value a Traveling Valve Test is performed—where the pumping unit is stopped at various points along the up-stroke and the dynamometer records how quickly the fluid load falls off the plunger.  Based off the speed of load-loss, the fluid slippage is calculated and displayed in BFPD (barrels of fluid per day).  This test is very valuable when trying to determine how worn a pump is and whether or not that pump wear warrants performing a pump change.  Similarly, a Standing Valve Test can be performed by stopping the rods during the down-stroke to see if the pump's Standing Valve is leaking.  If the Standing Valve is leaking (which allows fluid to drain out of the tubing), the Dynamometer will measure a load increase during the test.  As fluid leaks out of the Pump Chamber past the Standing Valve, the Traveling Valve ball will seat and the rods will begin to carry the fluid load—which is the reason the Dynamometer records a load increase during the test.

 

In the lower-left corner of the page displayed above, common examples of Pump Card shapes are displayed.  The ideal card is represented by a rectangle:  indicating the fluid load is rapidly picked up and held throughout the duration of the up-stroke, and then it is instantaneously released (onto the tubing) as the plunger begins the down-stroke.  Any deviation from this shape indicates inefficiencies and lost pump stroke.  As discussed on the above sheet, it is vitally important to understand that the only part of the downhole Stroke Length that contributes to the "pumping action" (or the displacement of new fluids into the tubing) is the Effective Plunger Travel.  Effective Plunger Travels only occurs in the center portion of the Pump Card when the Traveling Valve is open and the Standing Valve is closed, or vice versa.  This area is highlighted on the Gas Interference sample card (above). 

 

On many wells in the Permian Basin, the bottom portion of the tubing is not anchored (for fear of "planting" the TAC by setting it below fracked sand-producing formations)—but this is the only inefficiency that an oil operator will actually design into the system. This producing inefficiency is deemed to be acceptable when compared with the enormous potential costs (and risks) of a tubing fishing job.  Other than this, all the other pumping inefficiencies that reduce the Effective Plunger Travel should be avoided by the proper design of the downhole equipment and the operation of the well.

 

The main factors affecting the Pump Card are:  incomplete pump fillage, gas interference, tubing movement ("tubing breathing"), and excessive fluid slippage (indicating a worn pump).  The height of the Pump Card is a function the fluid load on the plunger, and the fluid load is a function of the plunger diameter and the hydrostatic Net Lift.  The area of the Pump Card is equivalent to the amount of work being performed by the pump. 

 

Additional information that also can be observed on a Pump Card include:  pump tagging (bottom or top), erratic valve action (due to solids/trash or a worn/pitted ball & seat), plunger sticking or excessive friction (due to solids in-between the plunger and barrel), and a few other anomalies.

Two General Categories of DynamometersHorseshoe Load Cells vs Quick-Install PRT Strain Gauges

A)  Horseshoe Dyno being installed between the Polished Rod Clamp & the Carrier Bar (Bridle).

Echometer Horseshoe Dynamometer being Installed on a Rod Pumping Well

B)  Echometer's PRT Dyno clamped onto the Polished Rod (below the PR-Clamp)

Echometer PRT Dynamometer Clamped onto the Polish Rod

It is important to note the distinguishing features of the two general categories of oilfield dynamometers:

  • Horseshoe (or Donut) Load Cell Dynamometer:  These load cells are placed between the Polished Rod Clamp and the Bridle—which requires the rod string first be stacked out on the wellhead to create separation for the dynamometer to be inserted (as shown in the image where the stack-off "suitcase" is resting on the stuffing box to support the rod load). With the Dyno being installed and the well returned back to pumping, the load cell acts like an ordinary bathroom scale and measures the true load on the polished rod.  A Donut Load-Cell operates similarly but it is used for continuous dynamometer acquisition with POC's (Pump Off Controllers) while the Horseshoe is made for temporary installation by a Well Tech. Understandably, a horseshoe dynamometer is more accurate than a PRT because it takes direct measurements of the polished rod load. However, horseshoe dyno's are not used as frequently as the PRT for routine diagnostic analysis due to many issues related with its installation (described below).

  • PRT (Polished Rod Transducer) Dyno:  This is Echometer's quick-install Dynamometer and is the most commonly used. The PRT does not directly measure the Polished Rod Load.  Rather it is a clamp-on strain-gauge that is screwed onto the polished rod and it measures the minute changes in diameter of the polished rod along the stroke length.  The rods carry the fluid load on the up-stroke but not on the down-stroke.  The added fluid load adds stress to the rod string and that axial stress causes a proportional radial diameter change.  Using Hooke's Law (which is a relationship between the radial strain caused by an axial stress) the minute changes in polished rod diameter are used to back-calculate the axial load causing the diameter change:  i.e. the fluid load.  Adding the fluid load to the calculated buoyant rod weight, the Surface Dyno is computed.  From this point on, the Wave Equation is used to calculate the Pump Card in the same fashion as the Horseshoe Load Cell.  Comparative studies performed by Echometer analyzing the accuracy of the PRT found it is within 2-3% of the loads recorded by the Horseshoe Load-Cell as long as accurate input data is used and there is no bending of the Polished Rod due to vertical misalignment (effects described below).

 

So....while Load Cell Dyno's are more accurate, their installation process creates other problems.  Usually Well Techs will only use the clamp-on PRT Dyno unless specific circumstances warrant more accurate information—at which point the Horseshoe Dyno can be installed. 

 

These reasons illustrate the installation issues associated with the Horseshoe Dyno:

  1. In order to install the Horseshoe, the well must have a good functioning brake.  This is needed when stacking the rods out on the wellhead.  

  2. It takes much more time to install:  A 2nd (stack-out) Polished Rod Clamp must be installed on the Polished Rod (shown in above image), lubricators or any other non-load bearing devices (if present) on top the stuffing box must be removed, & the stuffing box bolts must be tightened to protect the rubber packing before stacking out the rod weight.  After recording the data, these steps much be back-tracked to restore the well back to its original condition.  

  3. Due to stacking out the rod-string and the other steps involved, the liability risks of injury to the operator and/or well equipment are greatly increased.  

  4. The well is turned off during the installation process—which disturbs the well's normal run-time cycles causing the fluid level to build up and thus changes the downhole conditions.  This disturbance usually necessitates a Well Tech acquire longer periods of data so the well can re-stabilize (or risk acquiring unrepresentative data).  Also, this disturbance to the pumping cycles interferes with the ability to properly calibrate the time-clock to the well's production. 

  5. The disadvantages associated with raising the rod-string.  The rod-string is raised 3" by the addition of the Horseshoe underneath the polished rod clamp and this is disadvantageous for two reasons:

    • It changes the pump spacing.  This reduces the pump's compression ratio and can aggravate gas interference (making the acquired data look worse than it actually is during normal operation).  Or it can hide the fact that the well actually has a 2-3" tag on the pump during normal operation (which will be removed when recording the dyno).

    • Raising the rods 3" higher equally raises the plunger 3" higher relative to the pump barrel.  At the top of the upstroke, this will cause the plunger to move into an unswept area of the barrel—which can be problematic if the pump has been downhole a while and built-up scale deposits exist here. 

 

In contrast, the installation of the PRT Dyno is extremely easy and can even be performed while the well is pumping (which is necessary if there is no working break and unit is counter-weight heavy to where the horse-head always settles up when the unit is turned off).  

 

Now, lets evaluate the downsides of the PRT Dynamometer:

  1. PRT Data Accuracy:  The PRT data is not as accurate as the Horseshoe and is (slightly) more qualitative in nature when compared to the Horseshoe.  However, the PRT is sufficiently accurate for 95% of most work unless more precise measurements are needed for a particular situation, for example:  when performing a scientific analysis on the acquired data or when greater clarity in the numbers are needed for a well that is difficult to accurately diagnose.

  2. Polished Rod Bending:  if the polished rod is out of vertical alignment with the wellhead (or hits the horse-head at the top of the up-stroke), bending stresses will result in the polished rod.  These stresses will cause additional changes in the rod diameter—which the PRT naturally interprets as being "real" load changes occurring downhole.  If the polished rod is out of vertical alignment—the effect will cause the Pump Cards to slightly slant.  If the polished rod hits the horse head at the top of the up-stroke—there will be some form of anomalous load change during that side load (a good operator must recognize this while at the well site).  The distortions to the pump card are often subtle, but not always.  Thankfully, however, they usually do not prevent the accurate diagnosis of the downhole pump performance.  Sometimes these distortions can even be removed by repositioning the PRT in relation to the angle of bending.  

  3. Load/Temperature Drift:  The internal strain-gauge in the PRT is extremely precise in measuring minute changes in diameter but temperature changes on the strain gauge itself cause the gauge to expand or contract.  The good gospel news is:  the PRT recalibrates itself to zero each stroke (so the temperature change will cause little disturbance...unless your SPM is really really slow and there is a significant, sudden temperature change).  The problem with Temperature Drift is more pronounced during Valve Checks or performing counter-balance tests (where the zero recalibration process is not occuring as frequently).  Good operator practices can usually minimize this small annoyance.  

 

Downhole Diagnostic has both types of Dynamometers and can employ either one as needed.

Rod Pumping Optimization:  a few extracted slides from a training course...
 
Rod Pumping Optimization

Rod Pumping Optimization

Here are a few extracted slides from a Rod Pumping Optimization training course I performed (most of the slides pertain to Dynamometer Card Interpretation). I have many more slides on every tropic related to Sucker Rod Pumping and would be happy to help train your Engineers, field Foreman, Pumpers and Well Techs on whatever topics you are interested in.

Rod Pumping System Concepts

Rod Pumping System Concepts

Downhole Rod Pump

Downhole Rod Pump

Dynamometer Card Interpretation

Dynamometer Card Interpretation

Surface Dyno Card

Surface Dyno Card

Wave Equation to Calculate Pump Card

Wave Equation to Calculate Pump Card

Pump Dynamometer Card

Pump Dynamometer Card

Traveling & Standing Valve Action

Traveling & Standing Valve Action

Pump Card Interpretation

Pump Card Interpretation

Keys to Interpreting Pump Card

Keys to Interpreting Pump Card

Liquid vs Effective Pump Fillage

Liquid vs Effective Pump Fillage

Ideal Dynamometer Card: 100% Fillage

Ideal Dynamometer Card: 100% Fillage

Fluid Pound & Gas Interference

Fluid Pound & Gas Interference

Pump Wear & Delayed TV Closure

Pump Wear & Delayed TV Closure

Solids Sticking in Rod Pump

Solids Sticking in Rod Pump

Friction Dyno Cards:  Rod-on-Tubing

Friction Dyno Cards: Rod-on-Tubing

Gas Lock & Unique Card

Gas Lock & Unique Card

Consecutive Stks:  What's Happening?

Consecutive Stks: What's Happening?

"Can-Opener" Cards

"Can-Opener" Cards

Fluid Pound Dynamometer Cards

Fluid Pound Dynamometer Cards

Gas Interference Dyno Cards

Gas Interference Dyno Cards

Gas Lock Dynamometer Cards

Gas Lock Dynamometer Cards

Tag on Pump:  FG vs Steel Rods

Tag on Pump: FG vs Steel Rods

Plunger Spacing: Function of Fillage

Plunger Spacing: Function of Fillage

Up-Stroke Tag

Up-Stroke Tag

Destructive Pumping

Destructive Pumping

Incomplete Pump Fillage Spectrum

Incomplete Pump Fillage Spectrum

I Have Much More to Share

I Have Much More to Share

Shawn Dawsey @ Downhole Diagnostic

Shawn Dawsey @ Downhole Diagnostic

What the Dynamometer Survey Can Answer:

The Pump Card—in conjunction with the Fluid Level Survey—form the backbone of Well Diagnostic Analysis.  By determining if liquid resides above the pump & how effectively the pump is filling and displacing that liquid—the well's producing & lifting efficiency can be quantified and analyzed.  Based off the finding, the well can be optimized by making immediate operational changes (to the run-time, pump spacing or surface equipment) and downhole equipment changes can be planned for and made the next time the well is pulled.

 

The information operators are most frequently interested to find from a Dynamometer Analysis include:

  • Is the pump full of fluid throughout the run time?

  • If not, at what point during the run cycle does incomplete fillage begin?  

  • During incomplete fillage, does the Pump Card indicate Fluid Pound or Gas Interference?  And does the Pump Intake Pressure from the fluid level shot agree with the Pump Card shape and size?

  • What is the appropriate run-time for the well to get full production without damaging the equipment?

  • How effectively is the downhole gas separator working?

  • Is the well tagging bottom?  Or does severe gas interference warrant spacing the pump closer to bottom?

  • How worn is the pump and is it causing the well to lose production?

  • How much barrels of fluid per day does the Dyno interpret the pump is displacing?

  • Are any anomalies or anything else unusual indicated (pump sticking, excessive friction in the pump or rods, etc.)?

  • And are the sucker rods operating within mechanical limitations?

 

 

Incomplete Pump Fillage and Destructive Pumping Practices:

 

No dynamometer discussion would be complete without addressing the 3 most destructive pumping practices:  Fluid Pound, Gas Interference, & Pump Tagging.  If there is complete liquid fillage in the pump, the rod string is being stroked more than necessary.  For example, if the average pump fillage is 50%—the well is stroking twice as much as necessary.  Instead of running 80% of the day, it could produce that volume in 40% of the day with a full pump.  Let's take a look at all 3 in detail.

 

Three Destructive Pumping Practices:

 

Fluid Pound:  each impact load imparted to the pump’s plunger causes:  the rods to buckle and hit the tubing; high load impacts which beat out the Traveling Valve ball & seat; causes the pump's valve rod to buckle creating side-loading of the plunger onto the barrel; the stresses imparted in the rod drastically increase the Modified Goodman Rod Loading and reduce the rod life; and the impact load eventually transmits all the way up the rod-string and damages the tightly inter-locking teeth in the gearbox.

 

Gas Interference:  While Gas Interference (or "Gas Pound") is in many regards very similar to Fluid Pound, it does not create nearly the same type of impact loads—however, volumetrically:  it is just as inefficient.  And due to the inefficiency, the additional strokes required are the most damaging to the equipment.  Also, gas that enters the pump eventually makes its way up the tubing string and this is the most common cause of stuffing box leaks (due to gas heading the top of the tubing dry).  Gas Interference keeps Pumpers on their toes because the well's pump performance is often erratic.

 

Pump Tagging:  Light pump tags do have their place in the oilfield but should be avoided if possible.  All too often, a pumper reports to the office that a well has a "light" tag.  It might feel "light" at surface, but how light is that tag 2-miles downhole at the pump???  And when not periodically monitored, a "light" tag today often gets a little heavier a couple weeks down the road.  Since Fiberglass rod strings absorb much of the tag and do not transmit the shock wave vertically as effectively as steel does, a "light" tag on a FG Rod well might be twice as hard as "light" tag on an all steel rod string.   Usually the well is put on tag due to pumping problems related to gas interference but a much better way to resolve the situation is to design the gas interference out (either in the downhole gas separator or handle the gas in the pump's design).  Tagging is not only destructive to the pump, rods and tubing, but tagging also reduces the downhole Plunger Travel.  A 2" tag is 2-inches of lost downhole stroke.  Look at the example Gas Interference Dyno Report at the top of the page:  due to the small pumping unit, this well as loosing 7% of its total downhole stroke-length as a result of the tag.  Also, pump tagging tends to hammer the pump into the seating nipple (making it more difficult to unseat next pull) and the large impact forces can also turn the previously-set TAC loose (leading to additional inefficiencies). 

© 2020 by Dowhole Diagnostic  |  Midland, TX

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Leaking Standing Valve

Dynamometer Cards: The Standing Valve is partially leaking and the full fluid load is only released off the plunger in the middle of the down-stroke when the plunger is moving the fastest.