O. Lynn Rowlan, Carrie Anne Taylor and Ryan P. Craig
The pump stroke can be longer than the surface stroke when the dynamic motion of the beam pump system adds momentum to the rod string, resulting in the pump stroke length increasing. The pump stroke can be shorter than the surface stroke when sucker rods stretch to pick up the pump fluid load and other frictional forces. Rod stretch creates under travel dynamometer card shape. Pumping fast or high plunger velocities creates over travel cards.
Pump position in the barrel changes when the pump is not full compared to a stroke when the pump is filled with liquid. When incomplete pump fillage occurs, the plunger tends to over travels on the down stroke moving deeper into the barrel. In some cases tagging can occur due to pump spacing, plus increased over travel. This paper will use field collected dynamometer data to show excessive over-travel can occur on both the upstroke and the down stroke.