Abstract
Both the surface and the pump dynamometer cards are used to analyze sucker rod-pumped wells. Diagnostic pump card loads are calculated using the wave equation from the measured surface dynamometer load and position. The pump plunger fluid load, Fo, applied to the bottom of the rod string is directly related to difference in pressure across the plunger over the plunger area. Typical pump card loads plot near zero load when the traveling valve, TV, is open during the down stroke. When the standing valve, SV, is open during the upstroke the pump card loads should plot near fluid load determined using the pump intake pressure from a fluid level measurement. An expected fluid load maximum load line can be calculated by setting the pump intake pressure equal to zero.
The diagnostic pump card loads can be compared to these three reference load lines 1) Zero line, 2) Fo line from Fluid Level and 3) Maximum Fluid Load, Fo max, line. Certain downhole pump problems can be identified based on the location of the pump card loads with respect to these three load reference lines. If no load transfers between the TV and SV, then the diagnostic pump card becomes a flat shape. The location of the flat pump card can be used to determine if there is 1) the traveling valve could be stuck open, 2) a deep sucker rod string part occurs near the pump depth 3) the rods could be parted at a depth above the pump, 4) tubing could be dry, or 5) the SV could be stuck open.
If the pump intake pressure is low then the pump card load on the upstroke should plot near the Fo max reference load line. At a glance the location of the upstroke pump card loads can be used to estimate the pump intake pressure. Excessive downhole friction is indicated by the pump card displaying down stroke loads considerably below zero and upstroke loads substantially above the Fo from Fluid Level reference lines.
Incomplete pump fillage is often associated with a “pumped-off well”, meaning that the pump displacement exceeds the production capacity of the reservoir. There are other causes of partial liquid pump fillage: gas interference or the presence of a flow restriction in the annulus or excessive pressure drop at the pump intake.
This paper describes analysis methods used to compare the pump card diagnostic loads to the reference load lines. The analysis of the data can be used to identify the reason for lack of pump action or the cause of incomplete pump fillage. Several example field datasets will combine dynamometer and fluid level records to identify the source of the problem and presents recommendations for possible solutions. Use of downhole pump load and position is the basis of pump card diagnostic analysis and troubleshooting.
