Drill pipe/casing protector assembly

Abstract

A drill pipe/casing protector assembly for an underground drilling system comprises a well bore in an underground formation, a fixed tubular casing installed in the well bore, a rotary drill pipe extending through the casing and having an O.D. spaced from an I.D. of the casing (or well bore) during normal drilling operations, and a protective sleeve mounted around the drill pipe and spaced from the I.D. of the casing, and upper and lower thrust bearings affixed to the drill pipe above and below the sleeve to retain the sleeve in a fixed axial position on the drill pipe. The sleeve contacts the I.D. of the casing when the drill pipe deflects off-center to protect the casing from contact with the drill pipe or its tool joints during rotation of the drill pipe. Axial grooves in an I.D. wall of the sleeve allow fluid under pressure to circulate through a space formed between the I.D. of the sleeve and the O.D. of the drill pipe. Generally flat bearing surface regions on the I.D. wall of the sleeve between adjacent grooves are arranged in a polygon configuration for tangentially contacting the O.D. of the drill pipe around the sleeve I.D. The sleeve separates from the O.D. of the drill pipe upon circulation of a fluid film under pressure between the sleeve and drill pipe to produce a fluid bearing effect with reduced frictional drag. End slots at the top and bottom annular end walls of the sleeve provide enhanced fluid bearing effects in the clearance regions between the sleeve and the adjacent thrust bearings.