Paper: A Progress Report on Fluid Slippage in Down-Hole Rod-Drawn Oil Well Pumps

Fluid slippage is defined as the fluid that leaks past a metal plunger during the upstroke of a down-hole, rod-drawn, positive displacement pump. American Petroleum Specification 11AX covers this type of pump which is used in approximately 90% of artificially lifted wells. This paper will present the first part of the results of a continuing research project covering the theoretical analysis and laboratory testing of pump slippage. The goal of this project is to present a mathematical model which will accurately represent the actual down-hole slippage for this class of pump. The current results should be useful to operators for selection of clearances between metal plungers and barrels. In the review of literature many of the clearances and differential pressures were lower than what is normally experienced in light oil operations. Tested clearances that were reported in the literature were 0.007" or lower. This investigation will evaluate some new ground looking at larger clearances and higher differential pressures.