a method of pumping oil from wells by using a downhole pump without sucker rods. Subsurface hydraulic pumps consist of two reciprocating pumps coupled and placed in the well. One pump functions as an engine and drives the other pump (the production pump). Surface power is supplied from a standard engine-driven pump. The downhole engine is operated by clean crude oil under pressure (power oil) that is drawn from a power-oil or settling tank by a triplex plunger pump. If a single string of tubing is used, power oil is pumped down the tubing string to the pump, which is seated in the string, and a mixture of power oil and produced fluid is returned through the casing-tubing annulus. If two parallel strings are used, one supplies the power oil to the pump while the other returns the exhaust and produced oil to the surface. The hydraulic pump may be used to pump several wells from a central source and has been used to lift oil from depths of more than 10,000 ft.
