TWIN DRILL STEM Russian patent published in 2002 - IPC

FIELD: drilling of geologic-prospecting holes with use of twin drill stems, cleaning of sand obstacles in wells of oil fields by means of built-in apparatuses sunk on twin tubing string. SUBSTANCE: twin drill stem includes twin drill pipes. Each of them includes internal and external pipes arranged concentrically, their ends being fixedly joined to nipple and coupling. Butt surface of nipple has recess on side opposite to its threads which forms internal cylindrical protrusion that contacts end of internal pipe. Recesses forming internal cylindrical protrusions are made in coupling on opposite butts of which one can contact end of internal pipe and the other one, on side of thread in coupling, can contact butt of threaded cone of nipple of another twin drill pipe when twin drill pipes are screwed in stem. Through longitudinal conduits are made in bodies of nipple and coupling. EFFECT: enhanced functional reliability thanks to improved sealing and raised strength of twin drill stem. 3 dwg