Patent ID: 7610963

Claim:
A method of displacing a first fluid by means of a second fluid in a borehole in a ground wherein a feed pipe is located in the borehole and further wherein the feed pipe is connected to a piston body that is located between the feed pipe and a wall of the borehole wherein the feed pipe has a length defined between a first end and a second end, the method comprising the steps of: keeping the second fluid separate from the first fluid during a displacement; displacing the second fluid into an expandable space wherein the expandable space is defined by a closed membrane connected to the piston body and the feed pipe wherein the expandable space expands during an inflow of the second fluid wherein the second fluid is located in the expandable space following the displacement; and moving the piston body in a direction toward the first end of the feed pipe wherein the inflow of the second fluid into the expandable space expands the expandable space and further wherein expansion of the expandable space moves the piston body.