(19)
(11) EP 1 134 355 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
06.03.2002 Bulletin 2002/10

(43) Date of publication A2:
19.09.2001 Bulletin 2001/38

(21) Application number: 01113872.4

(22) Date of filing: 29.09.1995
(51) International Patent Classification (IPC)7: E21B 10/54, E21B 10/56, E21B 10/42
(84) Designated Contracting States:
BE DE FR IE

(30) Priority: 15.10.1994 GB 9420839

(62) Application number of the earlier application in accordance with Art. 76 EPC:
95306936.6 / 0707130

(71) Applicant: CAMCO DRILLING GROUP LIMITED
Stonehouse, Gloucestershire GL10 3RQ (GB)

(72) Inventors:
  • Fuller, John M.
    Nailsworth, Gloucestershire (GB)
  • Murdock, Andrew
    Stonehouse, Gloucestershire (GB)

(74) Representative: Bailey, Richard Alan 
A.R. Davies & Co., 27 Imperial Square
Cheltenham, Gloucestershire GL50 1RQ
Cheltenham, Gloucestershire GL50 1RQ (GB)

   


(54) Rotary drill bit


(57) A rotary drill bit comprises a bit body (10) having a shank (13) for connection to a drill string, a plurality of cutters (23) mounted on the bit body, each cutter having a cutting face (24, 25), and means for supplying drilling fluid to the surface of the bit body to cool and clean the cutters. At least some of the cutters (23) are lateral cutters located to act sideways on the formation being drilled, and the cutting faces (24, 25) of such lateral cutters are orientated to exhibit negative side rake and negative top rake with respect to the surface of the formation. The negative side rake angle is greater than 20° and may be as much as 90°, and the negative top rake angle is also more than 20°. A single cutter (23) may include two cutting faces (24, 25) at different negative side rake angles, e.g. the cutter may comprise a generally cylindrical substrate (26) formed at one end with two oppositely inclined surfaces (24, 25) meeting along a ridge, a facing table of polycrystalline diamond being bonded to the substrate surfaces and extending over the ridge.






Search report