Composite heavy metal drill collar

Claim 1

A composite drill collar adapted to form part of a drill pipe string used in drilling a bore hole in earth formations, comprising an elongate outer pipe member, upper connector means adapted to secure the upper end of said outer pipe member to an adjacent drill pipe member thereabove, lower connector means adapted to secure the lower end of said outer pipe member to a drill bit therebelow, a rigid elongate annular member in said outer pipe member having a specific gravity at least twice the specific gravity of said outer pipe member, said annular member being in a solid state when placed in said outer pipe member, means for preloading said annular member in radial compression by a temperature responsive shrink-fit of one of the members against the other of said members along substantially the entire length of said annular member within said outer pipe member before the composite drill collar is lowered in the bore hole, said outer pipe member having sufficient wall thickness whereby substantially all bending, torsion, compression, tension and impact loads are transmitted from the adjacent drill pipe member thereabove through said upper connector means to said outer pipe member and from said outer pipe member to said lower connector means and to the drill bit without being imposed on said annular member.