Hydraulic drilling apparatus and method

Hydraulic drilling apparatus and method suitable for use in a variety of applications including the drilling of deep holes for oil and gas wells and the drilling of vertical, horizontal or slanted holes, drilling through both consolidated and unconsolidated formations, and cutting and removing core samples. The drill head produces a whirling mass of pressurized cutting fluid, and this whirling fluid is applied to a discharge nozzle to produce a high velocity cutting jet. In one embodiment, the fluid is discharged from a central nozzle as a thin wall conical cutting jet, and a plurality of axially directed jets are spaced about the central nozzle for removing material within the circular groove cut by the conical jet. The conical jet can be used without the axially directed jets to cut core samples. In a second embodiment, the discharge nozzle comprises an oblique bore in a rotor which is driven at a relatively slow speed (e.g. 5-50 rpm) by the whirling fluid in the drill head. The direction of the borehole is controlled by side jets discharged in a radial direction from the distal end portion of the drill string which carries the drill head. The side jets are actuated in accordance with the curvature of the drill string. In one embodiment, the drill head is mounted on a carrier which can be withdrawn from the drill string and replaced while the drill string remains in the hole.