DOWN HOLE PRESSURE INTENSIFIER AND DRILLING ASSEMBLY AND METHOD

A jet assisted drill system which uses a high pressure intensifier (18), positioned in a down hole drill assembly (10). Drill fluid from a drill stem (12) is directed into the drill assembly (10), and in one mode this drill fluid is passed through the pressure intensifier (18) to cause a piston assembly (28) of the intensifier (18) to reciprocate, with the high pressure pistons (34) of the piston assembly (28) delivering high pressure drill fluid to a discharge jet (68) in the drill bit assembly (14). The low pressure fluid which drives the low pressure pistons (32) is discharged into a downstream annular passageway (56) and to the drill bit assembly (14). In a by-pass mode, a selector valve (60) directs drill fluid from an upstream passageway portion (48) directly to a downstream main passageway portion (56) to pass out the drill bit assembly (14). There is a control valve (62) to operate the piston assembly (28) and a trigger valve (64) to direct fluids selectively to the control valve (62).