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Abstract

The present invention provides a method and apparatus for controlling the production rate of a rotary downhole pump to prevent well pump-off. The method includes the steps of operating the pump at a first speed less than a maximum rate of the pump until well fluid is produced at the wellhead. The operation is continued at the first speed until a first dynamic fluid level in the annulus between the production tubing and the wellbore or the well casing is stabilized. A first static load on the drivehead at the first dynamic fluid level is determined. The pump is then operated at a second speed higher than the first speed until the fluid level in the annulus is stabilized at a second dynamic fluid level. A second static load on the drivehead at the second dynamic fluid level is determined. A linear function of the load on the drivehead is determined as a function of the fluid level in the annulus. The linear function is used to calculate a critical load on the wellhead at a pump off point of the well where the fluid level in the annulus is equal to the insertion depth of the pump. The speed of the pump is reduced when the critical load is reached to prevent pump-off. The method and apparatus of the invention provides for the monitoring and control of the well pumping operation to prevent pump-off without the need for downhole monitoring or measuring equipment.

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First Claim