Hydraulic piston-effect method and apparatus for forming a bore hole

A system for the formation of a bore hole, particularly for use in enhancing the recovery of oil from an oil bearing underground formation using an assembly including a piston sliding in a guide tube. The forward end of the piston body terminates in a drillhead including multiple ports for passing drilling fluid into the formation. Pressurized fluid flowing through the piston body applies pressure against the drillhead to cause it to move into the formation at the same time as it is cutting a pathway for itself. In a preferred embodiment, the forward end of the guide tube includes a whipstock through which the piston body turns from a vertical to a horizontal direction into the formation to provide a radial for the injection of steam. A rigid metal piston body may be used which plastically deforms when passing through the whipstock and becomes rigid thereafter as it moves through the formation.