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TIMER CONTROL OF BEAM PUMP RUN TIME REDUCES OPERATING EXPENSE
Presented at the Forty-Sixth Annual Southwestern Petroleum Short Course in Lubbock, Texas, April 21-22, 1999.
More than 400,000 wells in the United States operate with beam pump artificial lift equipment. Most of these wells have a pump capacity that exceeds the production rate of the well. Also, most of these wells pump 24 hours per day. These wells would operate more efficiently and at a lower cost with a device that reduces the amount of pumping unit operating time. This reduction in operating time decreases both electricity and maintenance costs.
Fluid flows into the wellbore when the pressure at the bottom of the wellbore is less than the pressure in the reservoir. In beam pumped wells, this liquid in the wellbore is removed by a reciprocating pump which has a capacity that is a function of pump size, pump stroke length, pumping speed, run time and other factors. In most beam pumped wells, the pump capacity exceeds the liquid producing capacity of the well. Therefore, the pump could be operated periodically and yet the pump would remove practically all of the liquid from the wellbore. While the well is shut-in, however, the pressure at the bottom of the well should be maintained at a low value compared to the reservoir pressure so that maximum inflow into the wellbore will occur.
It is important, when producing a well on intermittent operation, that the liquids above the formation and the bottomhole pressure be maintained at low values so that the desired maximum inflow of liquid into the wellbore will occur. Wells that operate 24 hours per day and have a pump capacity in excess of the well's producing rate "pound" liquid during the pump down stroke. This "pounding" of the pump plunger against the liquid causes vibration throughout the entire pumping system. The shock loading can cause rod buckling, pump wear, tubing wear, severe rod loading changes and pumping unit vibration even to the extent that the vibration can be visually observed and oftentimes even heard. These changes in loading are easily measured using a dynamometer system. Changes in rod loading on the downstroke also affect the pumping unit balance and motor power requirements. Longer life will be experienced by the pump, rods, tubing and pumping unit system if the plunger does not "pound" liquid near the middle of the down stroke. Operating the pumping system with a pump barrel full of liquid will result in longer equipment life.
This paper discusses various methods of controlling the operating time of electrically driven beam-pumped systems where the pump capacity exceeds the liquid producing capacity of the well. Two types of devices are commonly used to control pumping unit run time. An electrical manually-set on/off timer can be used to control when the pumping unit motor operates. Or, an automatic pump-off-control (P-O-C) device can monitor a parameter that relates to pump fillage and shut down the pumping unit motor when partial pump fillage or liquid no-flow is detected.
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