(19)
(11) EP 0 467 642 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
10.03.1993 Bulletin 1993/10

(43) Date of publication A2:
22.01.1992 Bulletin 1992/04

(21) Application number: 91306436.6

(22) Date of filing: 16.07.1991
(51) International Patent Classification (IPC)5: E21B 7/06, E21B 4/20, E21B 10/46
(84) Designated Contracting States:
BE DE FR GB NL

(30) Priority: 17.07.1990 GB 9015704
15.01.1991 GB 9100874

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

(72) Inventor:
  • Barr, John Denzil
    Cheltenham, Gloucestershire (GB)

(74) Representative: Carter, Gerald et al
Arthur R. Davies & Co. 27 Imperial Square
Cheltenham, Gloucestershire GL50 1RQ
Cheltenham, Gloucestershire GL50 1RQ (GB)


(56) References cited: : 
   
       


    (54) Earth drilling system and method for controlling the direction of a borehole


    (57) A steerable rotary drilling system for drilling or coring holes in subsurface formations comprises a bottom hole assembly 11 including a drill bit 13 carrying a plurality of cutting structures 16, and a mud hammer 14 which applies repeated axial impulses to the bit at a frequency greater than its frequency of rotation. Operation of the mud hammer 14 may be modulated in synchronism with rotation of the drill bit 13 and in controllable phase relation thereto. The drill bit is asymmetrically arranged, for example by an asymmetric distribution of the cutters 16, so that by appropriate selection of the phase relation the bit may be steered in a desired direction.






    Search report