Dynamometer Card: Diagnosing Sucker Rod Pump Performance

What Is a Dynamometer Card?

Dynamometer card (also called a pump card or rod pump diagnostic card) is a plot of the polished rod load versus rod displacement over one complete pump stroke cycle. Surface dynamometers measure the force on the polished rod at hundreds of points throughout each upstroke and downstroke, and the resulting closed loop shape is displayed as a card. The pattern of that shape reveals the mechanical condition of the downhole pump, the degree to which the pump barrel is filling with fluid, and any operational problems such as gas interference, fluid pound, or rod parting.

Key Takeaways

A dynamometer card plots polished rod load against rod position over one complete stroke, forming a closed loop whose shape diagnoses pump condition.
The ideal card has a parallelogram shape; deviations from that form indicate specific downhole problems.
Fluid pound produces a sharp spike at the bottom of the stroke where the plunger impacts liquid rather than gradually compressing a gas cushion.
Gas interference rounds the lower-left corner of the card as gas compresses before the traveling valve opens.
Wave equation analysis converts the surface dynamometer card into a calculated downhole pump card, isolating pump behavior from rod string dynamics.

How a Dynamometer Card Works

A surface dynamometer attaches to the polished rod just below the carrier bar of the pumping unit. It contains a load cell that measures axial force and a position sensor (linear transducer or accelerometer) that tracks rod displacement. Modern electronic units sample at high frequency throughout the stroke and transmit data wirelessly to a surface controller. The resulting plot is the surface dynamometer card, with rod position on the horizontal axis and load on the vertical axis.

Because the rod string is elastic and has mass, the loads measured at surface do not perfectly match the forces acting at the downhole pump. Wave equation analysis using the Gibbs method applies the one-dimensional wave equation to propagate the surface load and position data downward through the rod string, accounting for rod weight, buoyancy, stretch, and damping. The output is the downhole pump card, which directly shows when the traveling and standing valves open and close and how completely the pump barrel fills with fluid.

Pump fillage is calculated as the ratio of the effective fluid stroke to the theoretical maximum stroke of the plunger. A pump filling 100 percent produces a downhole card with sharp corners at both the top and bottom of the stroke. Reduced fillage results in a shorter effective stroke and lower fluid production than the pump geometry would otherwise allow.

Fast Facts: Dynamometer Card

Ideal shape: Parallelogram (sharp corners, flat top and bottom)
Fluid pound signature: Sharp load spike at bottom of stroke
Gas interference signature: Rounded lower-left corner, gradual load increase
Worn pump signature: Reduced area inside the card loop, low fillage
Rod parting signature: Load anomaly or sudden drop in peak load
Typical sampling rate: 100–500 data points per stroke
Analysis method: Gibbs wave equation (API RP 11L basis)
Primary output: Pump fillage percentage and production rate estimate

Field Tip:

When a well shows a fluid pound card, the first corrective step is usually to reduce pump speed (strokes per minute) rather than immediately pulling the pump. Slowing the unit gives the wellbore more time to refill between strokes. If the fillage improves and the card normalizes at lower speed, the well is simply pump-off limited and a pump-off controller can automate the optimal stroke rate going forward.

Common Dynamometer Card Patterns and Their Causes

Fluid pound occurs when the pump barrel does not fill completely with liquid during the downstroke, leaving a gas or vapor space above the standing valve. At the bottom of the stroke the plunger hits the fluid surface and the load spikes sharply. Repeated fluid pound generates severe shock loads that fatigue rod couplings and damage the pump seating nipple. Wells prone to fluid pound benefit from pump-off controllers that shut the unit down when fillage drops below a set threshold.

Gas interference appears when free gas enters the pump barrel along with liquid. During the compression phase of the downstroke, the gas must be compressed to standing valve cracking pressure before any fluid is displaced upward. The card shows a gradually rising load in the lower-left quadrant rather than the sharp corner of a properly filling pump. Severe gas interference can reduce pump efficiency to near zero. Remedies include lowering the pump below the perforations, installing a gas anchor, or reducing casing pressure to encourage gas separation.

Pumping Unit Balance and Card Analysis

Dynamometer cards also guide pumping unit counterbalance adjustments. The counterweights on a beam pumping unit are sized so the net torque on the gearbox is roughly equal on the upstroke and downstroke, minimizing peak torque and motor current. The surface dynamometer card shows the rod load at every crank position, which can be converted to torque on the gearbox crankshaft. Comparing upstroke and downstroke torque curves reveals whether the unit is over- or under-counterbalanced and how far to move the weights.

Modern rod pump control systems combine electronic dynamometers with automated pattern recognition algorithms to continuously monitor pump condition. Deviations from the learned baseline card trigger alerts without requiring a technician visit, enabling operators to prioritize well interventions on the wells that most need attention. Some systems also calculate rod stress at every connection in the string and flag connections approaching fatigue limits.

Dynamometer card is also referred to as:

pump card — common field shorthand for either the surface or downhole version of the plot
rod pump diagnostic card — formal descriptor used in engineering reports and API recommended practices
dyno card — informal abbreviation widely used by production engineers and rod pump technicians
downhole pump card — the wave-equation-calculated version showing actual pump conditions rather than surface measurements

Frequently Asked Questions About Dynamometer Cards

How often should dynamometer cards be pulled on a rod pump well?

Industry practice varies with well complexity and production value. High-rate or problematic wells may be tested monthly, while stable low-rate wells may only receive annual dynamometer surveys. Continuous electronic dynamometers eliminate the question by recording every stroke, but the economics of installing them are typically justified only on higher-value wells or where rod failures are frequent.

Can a dynamometer card estimate the actual oil production rate?

Yes. The downhole pump card area, combined with pump geometry (plunger diameter and stroke length), pump speed, and fluid properties, yields a volumetric flow rate calculation. This calculated rate is compared against tank gauge or LACT meter measurements to evaluate pump efficiency and estimate slippage past worn pump components.

What is the difference between a surface card and a downhole card?

The surface card shows what the load cell measures at the polished rod. It includes the influence of the rod string's own weight, inertia, and elasticity. The downhole card is mathematically derived from the surface card using wave equation analysis to remove those rod string effects, showing only the forces acting at the pump plunger. The downhole card is the definitive tool for diagnosing pump condition.

Why Dynamometer Cards Matter in Oil and Gas

Artificial lift by sucker rod pump accounts for more than 80 percent of all producing oil wells globally by count, and pump performance directly determines production revenue from those wells. Dynamometer analysis allows engineers to identify underperforming wells, prescribe the correct intervention, confirm that a workover achieved its objective, and optimize pump speed and counterbalance without pulling rods. The technology converts a mechanical observation into a quantitative diagnostic that drives lower lifting costs and fewer unnecessary workovers across the rod-lifted well inventory.