(19)

(11)

EP 0 215 880 A1

(12)

(43) Date of publication: 01.04.1987 Bulletin 1987/14 (21) Application number: 86901945.0 (22) Date of filing: 14.03.1986

(51) International Patent Classification (IPC):  E21B 41/ 00( . ) E21B 47/ 18( . ) (86) International application number: PCT/GB1986/000150 (87) International publication number: WO 1986/005543 (25.09.1986 Gazette 1986/21)

(84) Designated Contracting States: DE FR GB IT NL SE (30) Priority: 15.03.1985 GB 19850006833 (71) Applicant: GEARHART GEODATA SERVICES LTD. Dyce, Aberdeen AB2 OGL (GB)	(72) Inventor: HARRISON, James 14 Marcus Gardens Aberdeen (GB) (74) Representative: Hill, Cecilia Ann, et al  Abel & Imray Northumberland House 303-306 High Holborn London, WC1V 7LH London, WC1V 7LH (GB)