Abstract: Vertical reciprocation of the piston in a downhole well pump is hydraulically effected by surface-disposed power transfer apparatus comprising a driving fluid housing divided into first and second chambers by a drive piston reciprocably disposed therein, the first chamber being connected to the driving fluid chamber of the well pump by a driving fluid pipe. The pipe and the first housing chamber are filled with a first driving fluid. A driving fluid pump has an outlet connected to the second housing chamber, and an inlet connected to a source of a second driving fluid.

Abstract: A downhole well pump system comprises a reciprocating piston pump disposed in a fluid conduit in a wellbore which is filled with a driving fluid having a density preferably greater than the production fluid being pumped. The pump cylinder has a transverse partition and a piston assembly including an elongated piston rod extending through the partition and connected at its opposite ends to spaced apart pistons. The pump pistons and the cylinder partition divide the cylinder into a production fluid intake chamber, a production fluid transfer and delivery chamber, a driving fluid chamber and a second production fluid delivery chamber. Production fluid is conducted to the surface through a production fluid conduit disposed coaxial within the driving fluid conduit.