Controller for plunger lift system for oil and gas wells

Claim 1

A controller for a plunger lift system in which a pneumatically operated motor valve in the flow line of a producing well is opened intermittently to allow gas in the annulus between the well tubing and well casing to move a plunger through the tubing to the surface from a downhole position to force fluid in the tubing into the flow line, said controller comprising a microprocessing unit including a microprocessor, an A/D converter, and a programmable read only memory, a keyboard for programming the memory for a preselected period of off-time that the flow line valve is to be closed followed by a preselected period of on-time that the flow line valve is to be open during which latter time period the microprocessing unit causes pneumatic pressure to be supplied to the motor valve in the flow line to hold it open, pressure measuring means for continuously supplying the microprocessing unit with electrical signals proportional to the pressure in the casing annulus and in the flow line, and means responsive to a programmed maximum pressure in the casing annulus to reduce any remaining off-time to zero and open the valve in the flow line, means responsive to a programmed low casing pressure to cancel any remaining on-time to close the valve in the flow line, means responsive to programmed high or low pressure in the flow line to cancel any remaining on-time, if any, and close the flow line valve and to prevent the valve from being opened as long as the high or low pressure exists in the flow line, means for comparing the casing pressure signal with a programmed value for the expected pressure in the casing and to cancel any remaining on-time, if any, and close the flow line valve and prevent the valve from being opened when the pressure signal is such as to indicate a malfunction of the measuring means, and a battery for supplying the electrical power for the controller and means for comparing a fraction of the output voltage of the battery when fully charged with a preselected lower voltage and for preventing pneumatic pressure from being supplied to the motor valve when the voltage supplied by the battery drops below said preselected minimum.