Drilling apparatus with dual pipe and cross-over

Details Drilling apparatus with dual pipe and cross-over Drilling apparatus with dual pipe and cross-over

E - Fixed Constructions

21

B

255/25

E21B 17/00 (2006.01) E21C 7/08 (1980.01)

Patent

CA 1106356

ABSTRACT OF THE DISCLOSURE Apparatus is disclosed for drilling a pilot hole and subsequently enlarging the pilot hole in earth formation. A dual concentric pipe string is used for circulating air down- wardly through the outer pipe via a cross-over sub, through a pilot bit and upwardly through the bore hole outside the pipe string to bail cuttings, during drilling of the pilot hole. The air pressure expands the cutters of an expansible bit while a limited portion of the air supplied cools the cutters. After the cutters are fully expanded, additional air is utilized to clean and cool the cutters. Air is returned through the inner pipe of the dual concentric pipe string. A venturi device is utilized to induce return flow through the inner pipe during enlargement of the hole and to vacuum residue when enlargement is completed. The dual concentric pipe string is made up of lengths of pipe providing threaded, sealed joint.

341672

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