초록 ▼

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 The bit is withdrawn from the hole, and an expandable hole opener or underreamer run in the pilot hole with its cutters fully retracted and closely adjacent to each other.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 i

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 The bit is withdrawn from the hole, and an expandable hole opener or underreamer run in the pilot hole with its cutters fully retracted and closely adjacent to each other.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. Rotation of the hole opener continues while it is progressively lowered to drill the blast chamber down to the bottom or lower end of the pilot hole, the bottom of the blast chamber produced by the hole opener lying in substantially the same plane as the bottom of the pilot hole to collectively form a single blast chamber bottom.

대표청구항 ▼

A method of mining by forming blast chambers in earth formation, comprising drilling a pilot bore hole of a pre-selected diameter in the formation with a pilot drill bit and to a predetermined bottom depth, removing the drill bit from the pilot bore hole, then lowering on a pipe string a hole opener

A method of mining by forming blast chambers in earth formation, comprising drilling a pilot bore hole of a pre-selected diameter in the formation with a pilot drill bit and to a predetermined bottom depth, removing the drill bit from the pilot bore hole, then lowering on a pipe string a hole opener having initially retracted cutters in the pilot bore hole to an upper location spaced a pre-selected distance above the bottom of the previously formed pilot bore hole, circulating drilling fluid through said pipe string and expanding the cutters while rotating the hole opener to form an upwardly facing shoulder in said formation and lowering the hole opener to progressively remove said formation shoulder and enlarge the pilot bore hole progressively downwardly from said upper location to the bottom of said pilot bore hole to produce a substantially cylindrical blast chamber greater in diameter than the diameter of the pilot bore hole and having a bottom substantially coplanar with the bottom of said pilot bore hole, removing the hole opener from the bore hole, placing an explosive in the blast chamber; and detonating said explosive.