Abstract: A pilot hole of a preselected diameter is drilled with a suitable bit in an earth formation to a desired depth. The bit is withdrawn from the hole, and an expandable hole opener or underreamer run in the pilot hole with its cutters fully retracted and closely adjacent to each other. When the depth is reached at which enlargement of the pilot hole is to commence to produce a blast chamber, the cutters are forced laterally outwardly by fluid pressure while the hole opener is rotated, without moving the hole opener axially of the pilot hole, to cut the wall of the pilot hole and increase its diameter to the extent determined by maximum expansion of the cutters, thereby forming the upper end of the enlarged blast chamber.

Abstract: A borehole drilling apparatus adapted for connection to a drilling string, wherein the cuttings pass through the center of the drill bit and are adapted for conveyance to the surface through a central pipe of the drilling string, a labyrinth seal being located between the outer perimeter of the apparatus and the wall of the borehole to provide an annular region of relatively immobile or stagnant fluid around the apparatus to forestall movement of fluid upwardly and downwardly past the labyrinth seal, part of the drilling fluid being conducted in a downward direction below the seal to force cuttings toward and through the center of the drill bit for upward conveyance through the central pipe, another portion of the drilling fluid being discharged above the seal for upward conveyance through the annulus between the drilling string and wall of the borehole to the top of the latter, whereby any formation material which may drop into the borehole annulus will be forced upwardly through such annulus to the top of t

Abstract: The upper end of a rotary drill bit having initially retracted expansible cutters is connected to a stabilizer having initially retracted expansible stabilizer members, the upper end of the stabilizer being connectable to a rotary drill pipe string. The apparatus is lowered in a bore hole on the drilling string and rotated, the cutters being expanded to cut into the bore hole and enlarge it to a desired diameter, the apparatus being lowered to progressively continue enlarging the hole in a downward direction. Upon the stabilizer moving into the enlarged hole, its stabilizer members are expanded laterally to an extent conforming to the enlarged hole diameter, being engageable with the wall of the bore hole to stabilize the bit therebelow.

Abstract: An airhammer embodies an outer housing structure connectible to a rotatable drill pipe string through which compressed air is conducted. A hammer piston reciprocates in the housing structure, compressed air being directed alternately to the upper and lower ends of the piston to effect its reciprocation in the structure, each downward stroke inflicting an impact blow upon the anvil portion of an anvil bit extending upwardly within the lower portion of the housing structure. Upon elevating the airhammer off the bottom of the bore hole being drilled, the anvil bit drops downwardly of the housing structure to open one or more air bleeding grooves in the anvil bit, compressed air in the housing structure bleeding quickly through such grooves and preventing or stopping the hammer piston from reciprocating and impacting against the anvil bit.