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Oil & Gas Automation
is a publication
of Unico, Inc.

Since 1967

Unico, Inc.
3725 Nicholson Rd.
P. O. Box 0505
Franksville, WI
262.504.7396 fax

Unico is introducing a cost-effective inclinometer that measures beam angle and acceleration for about the price of a proximity switch. The compact, weatherproof unit mounts easily to a pump-jack beam and provides ±30° beam angle measurement, a 0° crossing logic signal, and beam acceleration measurement. Rod position can be determined

directly from beam angle or indirectly from pumping-unit geometry, beam zero crossing, and motor rotation. Beam acceleration is useful for diagnostics and for improving the dynamic regulation of the rod-stroking motion. For information on the inclinometer and its use in rod-pumping applications, please contact us.

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New Pump-Off Control (POC) Calculator Estimates Lost Production

Most rod-pumping units use some form of pump-off control (POC) to regulate production and maintain fluid in the well casing. The on/off duty cycle may be manually or automatically adjusted. A typical sequence runs a rod pump for a period of time to pull fluid from the well, which pulls down the fluid level in the casing. Eventually the fluid level will be drawn down to the pump intake and the pump will exhibit a pump-off condition. Automatic pump-off controllers will detect this condition and pause the pumping operation for a period of time. During this period of time, the fluid level rises in the casing.

Well inflow is a function of the fluid level in the well. The fluctuating level of fluid due to the pump-off control operation increases the average fluid height in the well and reduces its average inflow. Well production is dependent upon the average inflow, which can be significantly reduced at long pump cycle times.

Unico now provides an online POC Calculator™ to evaluate the effect of pump-off control settings on well production. The calculator supports both linear and Vogel inflow characteristics. The table below and charts at left illustrate the substantial loss of production for a typical set of well parameters.

These losses can be virtually eliminated with the use of a variable-speed drive. The bottom chart shows the operating paths for linear and Vogel characteristics during the pump on/off cycle. Unico variable-speed drives maximize well production by maintaining fluid level at the ideal operating point.

Try the POC Calculator™ at

Example POC Calculation

Input Parameter
  Results Value
Fluid Density (psi/ft)
  Linear Average Flow (bpd) 1006
Casing Diameter (in)
  Linear Lost Production (%) 16.2
Tubing Diameter (in)
  Vogel Average Flow (bpd) 1079
Reservoir Static Head (ft)
  Vogel Lost Production (%) 10.1
Reservoir Maximum Flow (bpd)
Pump Stop Head (ft)
Pump Output Flow (bpd)
Pump Off Time (s)

In Future Issues...

Look for the following articles in upcoming issues of Oil & Gas Automation Solutions:

Using a torque economizer mode to improve efficiency and reduce gearbox stress
Reducing power consumption and improving power factor of beam pumps
Field tests of methods to eliminate rod pump gas locking and interference
Detecting stick/slip oscillations that fatigue rod-string couplings and reduce energy efficiency of PCPs

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