(19)

(11)

EP 0 031 818 A1

(12)

(43) Date of publication: 15.07.1981 Bulletin 1981/28 (21) Application number: 80901133.0 (22) Date of filing: 02.07.1980

(51) International Patent Classification (IPC):  E21B 7/ 20( . ) E21B 43/ 10( . ) E21B 17/ 00( . ) (86) International application number: PCT/GB1980/000112 (87) International publication number: WO 1981/000132 (22.01.1981 Gazette 1981/02)

(84) Designated Contracting States: AT CH DE FR GB LI LU NL SE (30) Priority: 06.07.1979 GB 19790023645 (71) Applicant: IBALL, Eric Kingsley Wheathampstead, Hertfordshire (GB)	(72) Inventor: IBALL, Eric Kingsley Wheathampstead, Hertfordshire (GB)