Patent ID: 7191838

Claim:
A method of pumping liquid and gas from a well through a production tubing that has an inner sidewall which defines a production chamber, the production tubing extending downward from an earth surface within the well to a well bottom located within a subterranean zone which contains the liquid and gas that is supplied into the well at the well bottom by natural formation pressure, comprising: movably positioning a fluid displacement device within the production tubing; sealing the fluid displacement device to the inner sidewall to confine liquid to be lifted within production tubing above the fluid displacement device; moving the fluid displacement device upward and downward within the production chamber between an upper end of the production tubing at the earth surface and the lower end of the production tubing at the well bottom by applying gas to create opposite relative pressure differentials across the fluid displacement device within the production chamber to move the fluid displacement device in the production chamber between the upper and lower ends of the production tubing with the movement occurring in the direction of relatively lesser pressure; moving the fluid displacement device downward within the production chamber from the upper end to the lower end of the production tubing by applying gas at a relatively greater pressure above the fluid displacement device than the pressure below the fluid displacement device; and deriving the pressure of the gas applied above the fluid displacement device to move the fluid displacement device downward from gas supplied from the well by natural formation pressure.