(19)

(11)

EP 0 973 996 A1

(12)

(43) Date of publication: 26.01.2000 Bulletin 2000/04 (21) Application number: 98922712.9 (22) Date of filing: 08.04.1998

(51) International Patent Classification (IPC)7: E21B 47/04 (86) International application number: PCT/EP9802/187 (87) International publication number: WO 9845/574 (15.10.1998 Gazette 1998/41)

(84) Designated Contracting States: DE DK GB IT NL (30) Priority: 09.04.1997 EP 97201092 (71) Applicant: SHELL INTERNATIONALE RESEARCHMAATSCHAPPIJ B.V. 2596 HR Den Haag (NL)	(72) Inventor: DEN BOER, Johannis, Josephus NL-2288 GD Rijswijk (NL)