USE OF THE PUMP SLIPPAGE EQUATION TO DESIGN PUMP CLEARANCES

Test data collected from the TTU test well plus field data will be used to show the impact of pump clearance and pumping speed on pump slippage. Pump slippage significantly increases with increased well depth due to high temperature reducing water viscosity and increased differential pressure acting across the plunger. Specifying plunger length and other recommended practices will be discussed. A procedure to design the pump clearances based on sensitivity of the various correlating parameters will be presented. The Patterson Pump Slippage equation is discussed and a totally theoretically equation is shown to give similar slippage results which only adds to the credibility of the method. Pump efficiency can dramatically decreases at slow pumping speed when pump clearances are large. Additional energy must be input to the sucker rod pumping system to re-pump the portion of the pump's displacement lost to slippage. Even with the equations and guidelines available, the operator frequently uses too large of pump clearances for the well conditions and the reason for the low resulting production rate can be difficult to identify. Use of open or tight pump clearances should be based on well conditions. For large clearance pumps the efficiency decreases as the pumping speed is decreases plus the efficiency decreases when pumping from deeper depths.