(19)

(11)

EP 1 095 201 A1

(12)

(43) Date of publication: 02.05.2001 Bulletin 2001/18 (21) Application number: 99929616.3 (22) Date of filing: 01.07.1999

(51) International Patent Classification (IPC)7: E21B 10/56 (86) International application number: PCT/IB9901/229 (87) International publication number: WO 0001/916 (13.01.2000 Gazette 2000/02)

(84) Designated Contracting States: AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE (30) Priority: 06.07.1998 ZA 9805924 (71) Applicant: De Beers Industrial Diamonds (Proprietary) Limited Johannesburg 2001 (ZA)	(72) Inventors: TANK, Klaus Essexwold,2007 Bedfordview (ZA) BEX, Phillip, Alexander Camberley, Surrey SM4 6RF (GB) (74) Representative: Jones, Alan John et al CARPMAELS & RANSFORD43 Bloomsbury Square London, WC1A 2RA London, WC1A 2RA (GB)