(19)

(11)

EP 0 511 954 A1

(12)

(43) Date of publication: 11.11.1992 Bulletin 1992/46 (21) Application number: 90901911.0 (22) Date of filing: 26.01.1990

(51) International Patent Classification (IPC):  E21B 10/ 12( . ) E21D 9/ 10( . ) E21B 10/ 20( . ) (86) International application number: PCT/NO1990/000018 (87) International publication number: WO 1991/011588 (08.08.1991 Gazette 1991/18)

(84) Designated Contracting States: AT BE CH DE DK ES FR GB IT LI LU NL SE (71) Applicant: STEIN NARVESTAD A/S N-0611 Oslo 6 (NO)	(72) Inventor: NARVESTAD, Stein N-0667 Oslo (NO) (74) Representative: Avellan-Hultman, Olle  Avellan-Hultman Patentbyra AB P.O. Box 5366 S-102 49 Stockholm S-102 49 Stockholm (SE)