(19)

(11)

EP 0 909 363 A1

(12)

(43) Date of publication: 21.04.1999 Bulletin 1999/16 (21) Application number: 97918572.0 (22) Date of filing: 11.04.1997

(51) International Patent Classification (IPC):  E21B 7/ 08( . ) E21B 23/ 03( . ) E21B 17/ 02( . ) E21B 47/ 01( . ) (86) International application number: PCT/US1997/006044 (87) International publication number: WO 1998/046854 (22.10.1998 Gazette 1998/42)

(84) Designated Contracting States: FR GB NL (71) Applicants: Crawford, William B. Lafayette, LA 70503 (US) Crawford, Douglas W. Cushing, TX 75760 (US) Crawford, Mark S. Houston, TX 77069 (US)	(72) Inventors: Crawford, William B. Lafayette, LA 70503 (US) Crawford, Douglas W. Cushing, TX 75760 (US) Crawford, Mark S. Houston, TX 77069 (US) (74) Representative: Bayliss, Geoffrey Cyril, et al  BOULT WADE TENNANT, 27 Furnival Street London EC4A 1PQ London EC4A 1PQ (GB)