Method and apparatus for detecting well pump-off

Apparatus for monitoring the operation of a well pumping unit having a sucker-rod string and a power unit to reciprocate said rod string to produce fluid from an underground location, said apparatus comprising:

• first transducer means for generating a signal representative of a load on said rod string;
• second transducer means for generating a signal representative of a position of said rod string;
• means for using a maximum value and a minimum value of said load signal to establish a selected value corresponding to said load signal, and for using a maximum value and a minimum value of said rod signal to establish a reference position of said rod string;
• means for periodically updating said selected value by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal to obtain an updated selected value;
• means for periodically updating said reference position by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous minimum rod position signal to obtain an updated reference position;
• means for monitoring said load signal when said rod string reaches said updated reference position;
• and
• means for disabling said power unit when said value corresponding to said load signal exceeds said updated selected value with said rod string at said updated reference position.

Apparatus for monitoring the operation of a well pumping unit having a sucker-rod string and a power unit to reciprocate said rod string to produce fluid from an underground location, said apparatus comprising:

• first transducer means for generating a signal representative of a load on said rod string;
• second transducer means for generating a signal representative of a position of said rod string;
• a graph plotter for using said load signal and said position signal to produce a graph of rod string load vs. rod string position;
• means for entering a selected value corresponding to said load signal and a reference position of said rod string as a set point on said graph;
• means for periodically updating said selected value of said load signal by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal to obtain an updated selected value;
• means for periodically updating said reference position by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous minimum rod position signal to obtain an updated reference position;
• means for monitoring said load signal when said rod string reaches said updated reference position;
• and
• means for disabling said power unit when said load signal exceeds said updated selected value with said rod string at said updated reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string, means to reciprocate said string to pump fluid, means for generating a signal representative of a load on said rod string, and means for generating a signal representative of a position of said rod string, said method comprising the steps of:

• using said load signal to establish a selected value corresponding to said load signal;
• using said rod string position signal to establish a reference position of said rod string;
• updating said selected value periodically by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal;
• updating said reference position periodically by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous minimum rod position signal;
• and
• stopping said pumping unit when said value corresponding to said signal exceeds said updated selected value with said rod string at said upated reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string, means to reciprocate said string to pump fluid, means for generating a signal representative of a load on said rod string, and means for generating a signal representative of a position of said rod string, said method comprising the steps of:

• using said load signal to establish a selected value corresponding to said load signal;
• using said rod string position signal to establish a reference position of said rod string;
• updating said selected value periodically by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal;
• updating said reference position periodically by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous minimum rod position signal;
• monitoring said load signal when said rod string reaches said updated reference position;
• and
• stopping said pumping unit when said value corresponding to said signal exceeds said updated selected value with said rod string at said updated reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string, and means to reciprocate said rod string to pump fluid, said method comprising the steps of:

• generating a signal representative of a load on said rod string;
• generating a signal representative of a position of said rod string;
• using said load signal to establish a selected value corresponding to said load signal.
• using said string position signal to establish a reference position of said rod string;
• updating said selected value periodically by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal;
• updating said reference position periodically by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous minimum rod position signal;
• monitoring said load signal when said rod string reaches said updated reference position;
• and
• stopping said pumping unit when said valve corresponding to said load signal exceeds said updated selected value with said rod string at said updated reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string and means to reciprocate said rod string to pump fluid, said method comprising the steps of:

• generating a signal representative of a load on said rod string;
• generating a signal representative of a position of said rod string;
• using a maximum value and a minimum value of said load signal to establish a selected value of said load signal;
• using a maximum value and a minimum value of said string position to establish a reference position of said rod string;
• updating said selected value periodically by combining an updated maximum load signal with a previous maximum load signal and combining an updated minimum load signal with a previous minimum load signal;
• updating said reference position periodically by combining an updated maximum rod position signal with a previous maximum rod position signal and combining an updated minimum rod position signal with a previous mininum rod position signal;
• monitoring said load signal when said rod string reaches said upated reference position;
• and
• stopping said pumping unit when said load signal exceeds said upated selected value with said rod string at said updated reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string and means to reciprocate said rod string to pump fluid from a well, said method comprising the steps of:

• generating a signal representative of a load on said rod string;
• generating a signal representative of a position of said rod string;
• using said load signal to establish the rate of change in said load on said rod string as said rod string moves in a downward direction;
• selecting an average position of said rod string when said rate of change in said load has a maximum value with fluid filling said pumping unit;
• using said average rod string position and a minimum rod string position to determine a reference position of said rod string;
• and
• stopping said pumping unit when said rod string position is below said reference position at the time said rate of change of load has a maximum value.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string and means to reciprocate said rod string to pump fluid from a well, said method comprising the steps of:

• generating a signal representative of a load on said rod string;
• generating a signal representative of a position of said rod string;
• using said string position to establish a reference position of said rod string;
• using said load signals and said position signals to determine the position of said rod string when said load signal has a minimum value;
• monitoring the trend of movement of said rod position at said minimum load signal;
• and
• stopping said pumping unit when said rod position progressively moves downward at successive minimum load positions, to a position below said reference position.

A method of monitoring the operation of an underground well pumping unit, said unit having a sucker-rod string and means to reciprocate said rod string to pump fluid from a well, said method comprising the steps of:

• generating a signal representative of a load on said rod string;
• generating a signal representative of a position of said rod string;
• using said load signal and said position signal to determine the rod string position each time said load signal has a minimum value during the downstroke of said rod string;
• establishing a calibrate position of said rod string at a minimum load signal with fluid filling the pumping unit;
• using said calibrate position and a minimum rod string position to determine a reference position of said rod string;
• and
• stopping said pumping unit when said rod position progressively moves downward at successive minimum load positions, to a position below said reference position.