(19)

(11)

EP 0 030 975 A1

(12)

(43) Date of publication: 01.07.1981 Bulletin 1981/26 (21) Application number: 80901441.0 (22) Date of filing: 23.06.1980

(51) International Patent Classification (IPC):  E21B 4/ 02( . ) E21B 7/ 06( . ) E21B 49/ 06( . ) E21B 4/ 18( . ) E21B 44/ 00( . ) (86) International application number: PCT/US1980/000789 (87) International publication number: WO 1981/000018 (08.01.1981 Gazette 1981/01)

(84) Designated Contracting States: DE GB NL (30) Priority: 25.06.1979 US 19790051487 (71) Applicant: Standard Oil Company Chicago Illinois 60601 (US)	(72) Inventor: KILMER, Lauren G. Tulsa, OK 74105 (US) (74) Representative: Ritter, Stephen David, et al  Mathys & Squire 100 Grays Inn Road London WC1X 8AL London WC1X 8AL (GB)