Paper: Tubing Movement and Tubing Anchor Payout in Pumping Wells

The bottom of a string of unanchored tubing in a rod-pumped well moves up on the upstroke of the sucker rods and down on the down-stroke. The lower portion of the tubing string also buckles around the rods as they move up and goes straight as they start back down. Both vertical movement and buckling are caused primarily by those well pressures to which the tubing string is exposed. Decreased pump efficiency and abnormal rod, tubing, pump and casing wear are some of the detrimental results of this movement and buckling. Several past publications explain how a tubing anchor stops movement and keeps the tubing straight but none show how much this movement, which is actually the loss in pump stroke, might be. This paper first reviews the theories related to movement of the bottom of a string of freely hanging tubing in a pumping well and presents equations for calculating its amount. It then shows how a tubing anchor can be justified through increased production brought about by increased pump efficiency. Knowing the amount of cyclical movement will also give some indication of the reasons for excessive downhole wear. The paper also describes the various types of tubing anchors and includes some actual field cases which verify the advantages of anchoring tubing in rod-pumped wells.