(19)

(11)

EP 0 830 494 A1

(12)

(43) Date of publication: 25.03.1998 Bulletin 1998/13 (21) Application number: 95931870.0 (22) Date of filing: 27.09.1995

(51) International Patent Classification (IPC):  E21B 43/ 38( . ) (86) International application number: PCT/CA1995/000549 (87) International publication number: WO 1996/041065 (19.12.1996 Gazette 1997/03)

(84) Designated Contracting States: AT BE DE DK ES FR GB GR IE IT NL (30) Priority: 07.06.1995 US 19950478440 (71) Applicant: CENTRE FOR ENGINEERING RESEARCH INC. Edmonton, Alberta T6N 1E2 (CA)	(72) Inventor: PEACHEY, Bruce, R. Edmonton, Alberta T6J 5A1 (CA) (74) Representative: Watts, Peter Graham  Anthony Cundy & Co., 1623 Warwick Road Knowle, Solihull, West Midlands B93 9LF Knowle, Solihull, West Midlands B93 9LF (GB)