Three Conditions at the Pump Intake Resulting in Incomplete Pump Fillage

Lynn Rowlan

Echometer, Inc.

Abstract

The pump dynamometer card represents the fluid load the pump applies to the bottom of the rod string. The card is a plot of the calculated loads at various positions throughout a pump stroke. The fluid load applied to the rods by the pumpstarts to be transferred to the tubing beginning at the top of the stroke, when the down stroke begins. This load transfer occurs due to the sucker rod plunger compressing the gas and liquids inside the pump barrel between the closed traveling valve (TV) and closed standing valve (SV).

At the top of the stroke the SV just goes on the seat and the full fluid load is applied to the rods by the closed TV of the plunger. As the plunger moves down at the beginning of the down stroke, the pressure inside the pump barrel increases until the pressure inside the pump barrel exceeds the discharge pressure and the TV ball is unseated and the tubing pressure is now held by the closed SV.

The purpose of this presentation isto discuss incomplete pump fillage that occurs during the compression portion of the sucker rod pump cycle. The three causes of incomplete pump fillage are due to: 1) gas entry into the pump resulting in the condition identified as gas interference, 2) excess pump capacity resulting in a condition identified as fluid pound, and 3) flow into the pump is restricted or choked off due to the condition of a partially or completely blocked intake.

These three conditions can cause sudden deceleration of the pump and impact loading to the rod string, plus shock loading to other production equipment. The most common problems caused by incomplete pump fillage are: 1) rod buckling, 2) rod on tubing wear, 3) rod slap/coupling looseness, 4) low producing efficiency, 5) no production to surface, and 6) burned stuffing box.

These three pump conditions result in incomplete pump fillage and reason for incomplete pump fillage should be recognized to properly troubleshoot a well’s specific downhole problem. Thecharacteristic loads and shape of the pump card can be used by the dynamometer analyst torecognize the downhole conditions of: 1) gas interference, 2) fluid pound, or 3) blocked intake downhole.