7/24/2019 Oilfield Dynamometer Surveys_ Pump Card Interpretation & How They Work.pdf

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Example Dyno Survey Reports: Example 1: Hard Fluid Pound: 1-1/ 2" plunger m eet s t he f luid half -way @ 9. 1 SPM x 120". Example 2: Bad Gas I nt erf erence: well was put on a tag t o help pum p the gas, but not having m uch luck.Example Dyno Movie- showing well pum ping of f as recorded live in Echom et er's TAM sof t ware.

Page 2 of our Sucker Rod Pumping Short Course(see our Resources page t o download).

Dyno Survey

I f you want a concise summary of what a Dynam om et er is and how it works,click HERE t o go back t o t he Survices Page.

http://media.wix.com/ugd/f8ee70_668af4ec8fd340c8bf1d61ccfdabc3ac.pdfhttp://youtu.be/zuxLxlbTSHEhttp://www.downholediagnostic.com/http://media.wix.com/ugd/f8ee70_5008befc1e6342fb9fb15d59b393f461.pdf

7/24/2019 Oilfield Dynamometer Surveys_ Pump Card Interpretation & How They Work.pdf

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How a Dynamometer Works:

A Dynamomet er i s a di agnost i c devi ce used on S ucker Rod P umped Wel ls t hat measures t he l oad on t he t op rod (P ol ished Rod) andplots this load in relation to the polished rod position as the pumping unit moves through each strok e cy cle. The plot of the polishedrod 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 unitgeometry and the direction of rotation), the mechanical friction of the rods-on-tubing (and the rods on paraffin, etc), and the viscousfrictional forces generated between the rods and fluid. With the Surface Card being affected by so many different factors, therei s no "standardized" shape to Surface Cardswhich greatly inc reases 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 Cardshown in the top left corner of the sheet above (50% Fiberglass rod string).

A l t hough t here i s some val ue t o be gat her f rom t he S urf ace Card, oi l operat ors are much more i nt erest ed t o know what i s happeni ngdownhole at the pump. After all, the only reason for having any of the s urface or downhole equipment is to effectively actuate thedownhole 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] provideda solution to this problem when he developed the Wave Equation. The Wave Equation models the elastic behavior of the rod stringin its dynamic motionwhich allows the surface measurements acquired from the polished rod to be waved downhole to the pumpto generate a plot of the Load vs Pos ition on the pump's plunger. This plot is known as the downhole Pump Card. The beauty of theWave Equation is that it allows surface data to be acquired (which is easily accessible and inexpensive) and then mathematicallyfilters the data to illustrate the downhole pump performance each strok e. By filtering out the effects of the rod-string and every thingelse occurring above the pump's plunger, the Wave Equation essentially standardizes the various shapes the Pump Card can takeand greatly improves the ability of the pump performance to be properly diagnosed. However, interpretation can still be difficult attimes 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 (byTheta) & SRod (by Lufkin). These programs give the rod designer a great deal of control and versatility in simulating variousdownhole conditionsallowing for the prediction of mechanical stresses on each rod taper and the expected producing performanceof the pumping sys tem. These programs can be quite pricey. For those who do not need to perform many complicated designsimulations, it is worth noting that Echometer provides a completely free software that solves the Wave Equationknown as QRod. Compared to other programs, QRod is much more simplified with fewer design controls, but the accuracy of its computations iscomparable 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 theamount of Fluid Slippage leaking by the pump's plunger. When both upper corners of the Pump Card are rounded-off Fluid Slippageis indicatedbut the Pump Card in itself does not provide a means of determining how much s lippage is occurring. In order toquantify this value a Traveling Valve Test is performedwhere 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 fluidslippage is calculated and displayed in BFPD (barrels of fluid per day). This test is v ery valuable when trying to determine how worna pump is and whether or not that pump wear warrants performing a pump change. Similarly, a Standing Valve Test can beperformed by stopping the rods during the down-stroke to s ee if the pump's Standing Valve is leaking. If the Standing Valve isleaking (which allows fluid to drain out of the tubing), the Dynamometer will measure a load increase during the test. As fluid leaksout of the Pump Chamber past the Standing Valve, the Traveling Valve ball will seat and the rods will begin to carry the fluid loadwhich 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 isrepresented by a rectangle: indicating the fluid load is rapidly picked up and held throughout the duration of the up-stroke, and then itis instantaneously released (onto the tubing) as the plunger begins the down-stroke. Any deviation from this shape indicatesinefficiencies and lost pump stroke. As disc ussed on the above sheet, it is vitally important to understand that the only part of thedownhole Stroke Length that contributes to the "pumping action" (or the displacement of new fluids into the tubing) is the EffectivePlunger Travel. Effective Plunger Travels only oc curs in the center portion of the Pump Card when the Traveling Valve is open andthe Standing Valve is clos ed, or vice vers a. 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 belowfracked 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 j ob. Ot her t han t hi s, al l t he ot her pumpi ng i neff i ci enci es t hat reduce t he E f f ect ive P l unger Travel shoul d be avoi ded by t he 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 exces sive fluid slippage (indicating a worn pump). The height of the Pump Card is a function the fluid load on the plunger, andthe fluid load is a function of the plunger diameter and the hydrostatic Net Lift. The area of the Pump Card is equivalent to the amountof 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 ac tion(due to solids/trash or a worn/pitted ball & seat), plunger sticking or excessive friction (due to solids in-between the plunger andbarrel), and a few other anomalies.

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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 Bridlewhich requires the rod string first be stacked out on the wellhead to create separation for the dynamometer to be inserted (asshown in the image where the stack-off "suitcase" is resting on the stuffing box to support the rod load). With the Dyno beinginstalled and the well returned back to pumping, the load cell acts like an ordinary bathroom scale and measures the true load onthe polished rod. A Donut Load-Cell operates similarly but it is used for continuous dynamometer acquisition with POC's (PumpOff Controllers) while the Horseshoe is made for temporary installation by a Well Tech. Understandably, a horseshoedynamometer is more accurate than a PRT because it takes direct measurements of the polished rod load. However, horseshoedyno'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. ThePRT does not directly measure the Polished Rod Load. Rather it is a clamp-on strain-gauge that is screwed onto the polishedrod and it measures the minute changes in diameter of the polished rod along the stroke length. The rods c arry the fluid load onthe up-stroke but not on the down-stroke. The added fluid load adds stress to the rod string and that axial stress causes aproportional radial diameter change. Using Hooke's Law (which is a relationship between the radial strain caused by an axialstress ) the minute changes in polished rod diameter are used to back-c alculate 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, theWave Equation is used to calculate the Pump Card in the same fashion as the Horseshoe Load Cell. Comparative studiesperformed by Echometer analyzing the accuracy of the PRT found it is within 2-3% of the loads recorded by the HorseshoeLoad-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 c reates other problems. Usually Well Techs will only usethe clamp-on PRT Dyno unless specific circumstances warrant more accurate informationat which point the Horseshoe Dyno canbe 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 stack ing 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, & thestuffing box bolts must be tightened to protect the rubber packing before stack ing 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 equipmentare greatly increased.

4. The well is turned off during the installation process which disturbs the well's normal run-time cycles c ausing the fluid level tobuild 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 cyclesinterferes 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 Horseshoeunderneath 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 theacquired 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, thiswill cause the plunger to move into an unswept area of the barrelwhich can be problematic if the pump has beendownhole 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 isnecessary if there is no working break and unit is counter-weight heavy to where the horse-head always settles up when the unit isturned 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 precisemeasurements 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 theup-stroke), bending stress es will result in the polished rod. These stres ses will caus e additional changes in the rod diameterwhich the PRT naturally interprets as being "real" load changes occ urring downhole. If the polished rod is out of verticalalignmentthe effect will cause the Pump Cards to slightly slant. If the polished rod hits the horse head at the top of the up-strokethere will be some form of anomalous load change during that side load (a good operator must recognize this while at thewell site). The distortions to the pump card are often subtle, but not always. Thankfully, however, they usually do not prevent the

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

B) Echometer's PRT Dyno clamped onto thePolished Rod (below t he PR-Clamp)

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

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