Method and system for energy recovery from a rod pump

A method for energy recovery from a rod pump having a rod string, a hydraulic cylinder having a cylinder barrel with a pressure chamber and a piston located for reciprocating movement within the cylinder barrel and connected to the rod string such that the rod string reciprocates with the reciprocating movement of the piston to perform a pumping action, the method comprising:

• actuating a variable speed drive to rotate a variable speed reversible motor-generator in a reverse direction in a generator mode in which a weight of the rod string lowers the piston in a rod string downstroke to pump hydraulic fluid from the pressure chamber through the reversible hydraulic pump to rotate the reversible hydraulic pump in a reverse direction such that the motor-generator rotates in a reverse direction to generate electricity;
• and
• modulating a speed of the variable speed reversible motor-generator by the variable speed drive during the downstroke to modulate a speed of the reversible hydraulic pump to control a rate of flow of hydraulic fluid from the pressure chamber through the reversible hydraulic pump and thereby modulate a rate of downward motion of the piston and the rod string.

A method for energy recovery from a rod pump having a rod string including a polished rod, a hydraulic cylinder having a cylinder barrel, a piston located for reciprocating movement within the cylinder barrel and connected to the rod string such that the polished rod reciprocates with the reciprocating movement of the piston to perform a pumping action, and a pressure chamber in the cylinder barrel, the method comprising:

• actuating a variable speed drive to operate a variable speed reversible motor-generator in a generator mode in which a weight of the rod string lowers in a downstroke and displaces the piston in the cylinder barrel to pump hydraulic fluid from the pressure chamber through the reversible hydraulic pump, which rotates the reversible hydraulic pump and the variable speed reversible motor-generator in a reverse direction such that the variable speed reversible motor-generator generates electricity;
• and
• modulating by the variable speed drive a rate of flow of the hydraulic fluid from the pressure chamber through the reversible hydraulic pump solely by the variable speed drive modulating a reverse speed of rotation of the variable speed reversible motor-generator, which modulates the reverse rotation of the reversible hydraulic pump during the downstroke to control a rate of flow of hydraulic fluid through the reversible hydraulic pump.