Developing plunger slippage equation for rod-drawn oil well pumps



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A calculation is needed to predict pump slippage in a rod pumped well. Slippage lubricates the pump plunger and barrel and prevents galling of metals. Additionally, an estimate of plunger leakage is necessary to calculate pump efficiency. If the leakage is too small, the plunger and barrel are not properly lubricated; too much leakage causes low volumetric efficiency thus low power system efficiency. Historical plunger leakage equations have been proven incorrect by recent testing. A theoretical method has been developed to calculate pump slippage, but a new experimentally derived formula is needed.

Historical pump slippage formulas predict slippage that varies by a factor of 20 or more depending on the pump and fluid variables. Most of these formulas were derived from experimental data gathered in the 1930’s and 1940’s. A formula developed in the late 1990’s by ARCO and Harbison Fischer predicts a slippage that is much less than slippage predicted by the older historical formulas. The ARCO- Harbison Fischer formula was considered to be incomplete because a very limited amount of data was collected and pumping speed was not a variable that was studied. It is believed from theory and field practice that pumping speed does not affect slippage.

The purpose of this dissertation will be to develop a new slippage equation that is usable in the field and to gain a better understanding of the fundamentals of fluid slippage. This will be done using extensive test data from a test well and by improving upon past theoretical equations and by developing new theoretical equations from lessons learned from the well test.