(19)

(11)

EP 0 642 624 A1

(12)

(43) Date of publication: 15.03.1995 Bulletin 1995/11 (21) Application number: 94911732.0 (22) Date of filing: 28.03.1994

(51) International Patent Classification (IPC):  E21B 21/ 06( . ) E21B 49/ 00( . ) E21B 47/ 04( . ) (86) International application number: PCT/US1994/003343 (87) International publication number: WO 1994/023180 (13.10.1994 Gazette 1994/23)

(84) Designated Contracting States: FR GB NL (30) Priority: 26.03.1993 US 19930037918 13.08.1993 US 19930106368 (71) Applicant: WESTERN ATLAS INTERNATIONAL, INC. Houston, TX 77042-3115 (US)	(72) Inventors: GEORGI, Daniel, T. Houston, TX 77079 (US) ROBERTSON, Homer, A. The Woodlands, TX 77380 (US) FRANKS, Mark, S. Sugar Land, TX 77479 (US) (74) Representative: Wain, Christopher Paul  A.A. THORNTON & CO. Northumberland House 303-306 High Holborn London WC1V 7LE London WC1V 7LE (GB)