Patent ID: 7055631
Filing Date: 2006-06-06
Classification: E21B

Abstract:
1. An underground drilling system comprising: a wellbore in an underground formation; a fixed tubular casing installed in the wellbore; a rotary drill pipe extending through the casing and having O.D. spaced from an I.D. of the casing or wellbore during normal drilling operations; a protective sleeve mounted around the drill pipe having a hardness in the range of 75 to 123 Rockwell R; thrust bearing collars rigidly affixed to the drill pipe above and below the sleeve for maintaining the sleeve in a fixed axially position on the drill pipe; the protective sleeve mounted to the drill pipe via an internal sleeve I.D. configuration allowing the rotary drill pipe to continue rotating within the sleeve at a rotation rate sufficient to conduct drilling operations in the formation; said internal configuration comprising longitudinally extending and circumferentially spaced apart axial grooves formed in an I.D. wall of the sleeve for allowing fluid to circulate through a space formed between the I.D. of the sleeve and the O.D. of the drill pipe; at least one low-friction abrasion-resistant end pad formed on at least one end of the protector sleeve to reduce friction between the end of the protector sleeve and an adjacent end of the thrust bearing collar.