Constant horsepower regenerative assist for a hydraulic rod pumping unit

A hydraulic pumping unit for removing well fluids from a well, comprising:

• a drive motor having a rotary shaft for turning in a first angular direction;
• a reservoir for a hydraulic fluid;
• an accumulator for storing potential energy in response to receiving the hydraulic fluid;
• a sucker rod assembly disposed in the well for removing the well fluids from the well;
• a ram connected to said sucker rod assembly for moving in an up-stroke from a retracted position to an extended position and moving said sucker rod assembly from a downward position to a raised position, and moving in a down-stroke from said extended position to said retracted position with said sucker rod assembly moving from said raised position to said lowered position;
• a ram pump connected to said rotary drive shaft, said ram pump having a ram pump suction port connected to said reservoir and a ram pump discharge port connected to said ram for during the up-stroke of said ram transferring the hydraulic fluid from said reservoir into said ram and moving said ram from said retracted position to said extended position, and during the down-stroke transferring the hydraulic fluid from said ram into said reservoir;
• an accumulator pump connected to said rotary drive shaft, said accumulator pump having an accumulator pump suction port connected to said reservoir and an accumulator pump discharge port connected to said hydraulic accumulator for transferring the hydraulic fluid from said reservoir into said accumulator and storing potential energy in said hydraulic accumulator during the down-stroke of said ram, and during the up-stroke transferring the hydraulic fluid from said accumulator into said reservoir;
• said ram and said accumulator pumps each having a drive shaft, a cylinder block, a plurality of pistons, a swash plate and a port plate, said drive shaft coupled to said rotary drive shaft, said cylinder block mounted to said first drive shaft for rotating with said first drive shaft and engaging said port plate, said cylinder block adapted for movably receiving a plurality of pistons, with said pistons adapted for being moved by said swash plate to displace the hydraulic fluid within said cylinder block with rotation of said cylinder block and said first drive shaft, and said port plate engaging said cylinder block for passing the hydraulic fluid between a pump suction port and a pump discharge port depending upon angular positions of said cylinder block relative to said port plate;
• at least one control unit adapted for controlling flow rates of the hydraulic fluid through said ram pump and said accumulator pump, and adapting said ram pump for pumping the hydraulic fluid into said ram during the up-stroke and during the down-stroke passing the hydraulic from said ram into said reservoir and turning said rotary shaft in said first angular direction to power said accumulator pump in response to pressures within said ram provided by the weight of said sucker rod assembly in combination with said drive motor, and adapting said accumulator pump for pumping the hydraulic fluid into said accumulator during the down-stroke and during the up-stroke passing the hydraulic fluid from said accumulator into said reservoir and turning said rotary shaft in said first angular direction to power said accumulator pump in response to pressure within said accumulator in combination with said drive motor.

A method for operating a pumping unit, comprising the steps of:

• providing a ram and a sucker rod assembly, wherein the sucker rod assembly and the ram are located at a well head and configured for lifting well fluids from within the well,
• further providing a control unit, a drive motor, a ram pump, an accumulator pump, a reservoir for a hydraulic fluid, and an accumulator for receiving the hydraulic fluid and storing potential energy in response thereto, wherein the control unit, the drive motor, the reservoir, the ram pump, the accumulator pump and the accumulator are configured for moving the hydraulic fluid between the reservoir and the hydraulic ram for lifting and lowering the sucker rod assembly, and for moving the hydraulic fluid between the accumulator and the reservoir;
• connecting the ram pump, the accumulator pump and the drive motor to a rotary shaft for rotating in one angular direction during both an up-stroke and a downstroke of the ram;
• operating the ram pump to move the hydraulic fluid from the reservoir into the ram, lifting the sucker rod assembly, wherein the ram pump is powered by the drive motor in combination with the accumulator pump;
• releasing the hydraulic fluid from the ram into the ram pump and to the reservoir, and thereby providing mechanical power in combination with the drive motor for turning the rotary shaft which powers the accumulator pump to move the hydraulic fluid into the accumulator;
• controlling the flow of the hydraulic fluid from the ram, through the ram pump and into the reservoir, and the flow of fluid into and out of the accumulator;
• and
• wherein potential energy is recovered from the sucker rod assembly when disposed in a lifted position and used to operate the accumulator pump and store at least part of the potential energy for assisting in the up-stroke.