O. Lynn Rowlan, Gustavo, and Carrie-Anne Taylor
Echometer Company
Sheldon Want, McCoy School of Engineering
Slow strokes per minute, open pump clearances in a deep well have impacted the shape of the pump card and frequently results in the question: "Is my tubing unanchored?". The Coefficient of Tubing Stretch, Kt, and the downhole pump dynamometer card can be used to help identify unanchored tubing. The Unanchored Kt and Anchored Kt lines plotted on the left side of the pump card shape are the first step in resolving if tubing is anchored.
Excessive mechanical friction from doglegs created when drilling the well in the upper section of the wellbore can result in erroneous load measurement when initially setting the tubing anchor. Setting a tubing anchor should be done by pulling inches of stretch and should not be done using a load measurement gage.
Slippage and/or a leaky pump can make identifying unanchored tubing difficult, because the left side of the pump card dynamometer card leans to the right in a similar fashion as unanchored tubing. A static traveling valve load test is a common field technique to determine if a leaky pump is present. The Patterson Slippage equation was developed to calculate pump slippage for the entire stroke. If a portion of the Patterson slippage can be allocated to the left side of the pump card stroke, where the fluid load is transferred from the tubing to the sucker rods; then a pump slippage line could be plotted and be used as an additional aid in identifying slippage plus anchored or unanchored tubing.
Understand if my tubing anchor is properly set is important in long sucker rod and tubing run life. This paper will use many examples pump cards acquired from various sucker rod lifted wells to explain if tubing is unanchored or does the pump card shows tubing movement, unanchored tubing, excessive slippage or does this shape show this some other issue.