TWIN DRILL STEM AND PROCESS OF MANUFACTURE OF TWIN DRILL PIPE FOR TWIN DRILL STEM Russian patent published in 2002 - IPC

FIELD: drilling of geological prospecting holes with use of twin drill stems, cleaning of sand obstacles in wells of oil deposits with employment of built-in apparatuses lowered on twin tubing. SUBSTANCE: twin drill stem includes twin drill pipes. Each twin drill pipe has internal and external pipes placed concentrically, their ends permanently joined to nipple and coupling, recess forming internal and external cylindrical protrusions is made in butt surface of nipple on side opposite to its thread. Internal protrusion is fixedly joined to internal pipe and external protrusion is fixedly joined to external pipe. Recesses forming internal cylindrical protrusions are made in coupling in opposite face sides. One protrusion is fixedly joined to internal pipe, the other protrusion, on side of thread, contacts butt of cone of nipple of another twin drill pipe while twin drill pipes are screwed in stem. Through longitudinal conduits are made in bodies of nipple and coupling. Process of manufacture of twin drill pipe for proposed twin drill stem consists in installation of internal drill pipe carrying concentrators set concentrically in space of external pipe. Nipple is first welded to internal pipe before installation, then internal pipe is put into external pipe and the latter is welded to nipple. Later free ends of internal and external pipes are simultaneously welded to coupling. EFFECT: enhanced functional reliability thanks to improved sealing and increased strength of twin drill stem. 2 cl, 3 dwg