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(11) | EP 0 209 217 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Apparatus and method for forming an enlarged underground arcuate bore and installing a conduit therein |
| (57) An apparatus and method for drilling a pilot bore hole (B) along an underground
arcuate path (P) between two surface locations (0, E). The pilot bore hole (B) is
drilled in one direction with a drill string (10) having a leading pipe section (10A)
of a reduced diameter to provide increased flexibility. Upon completion of the pilot
bore hole (B), a reamer (48) connected to a product conduit (46) is connected to the
drill string (10). Drill string (10) pulls the reamer (48) and product conduit (46)
along the pilot bore hole (B) in an opposite direction for enlarging the bore hole
(B) to receive the product conduit (46). A spud bit (34) has a flat or blunt leading
end portion (34A) with a discharge opening (34D) therein to discharge high velocity
drilling fluid into the formation at a location offset from the longitudinal axis
of the drill string (10) to assist in guiding the drill string (10). An in-hole hydraulic
motor (70) is provided in an embodiment (Fig. 7) for rotating the drill bit (78),
and the longitudinal axis of a drive shaft (74) for the drill bit (78) is offset from
the longitudinal axis of the drill pipe string (10) to assist in a deviation of the
drill bit (78). |