(19)

(11)

EP 2 576 961 A2

(12)

(88) Date of publication A3: 19.01.2012 (43) Date of publication: 10.04.2013 Bulletin 2013/15 (21) Application number: 11724721.3 (22) Date of filing: 27.05.2011

(51) International Patent Classification (IPC):  E21B 29/08(2006.01) E21B 33/06(2006.01) (86) International application number: PCT/GB2011/051005 (87) International publication number: WO 2011/148191 (01.12.2011 Gazette 2011/48)

(84) Designated Contracting States: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR (30) Priority: 13.08.2010 US 373734 P 29.06.2010 US 359746 P 28.05.2010 US 349660 P 28.05.2010 US 349604 P (71) Applicant: National Oilwell Varco, L.P. Houston, Texas 77036 (US)	(72) Inventors: SPRINGETT, Frank Benjamin Spring TX 77379 (US) ENSLEY, Eric Trevor Cypress TX 77433 (US) JOHNSON, Christopher Dale Cypress TX 77429 (US) PETERS, Shern Eugene Houston TX 77066 (US) (74) Representative: Casbon, Paul Richard  Lucas & Co 135 Westhall Road GB-Warlingham, Surrey CR6 9HJ GB-Warlingham, Surrey CR6 9HJ (GB)