FIELD: oil and gas industry.
SUBSTANCE: device includes heavy-weight drill pipe (HWDP) serving as carrying part of the main drilling assembly and having on one side the window open outwards, secondary drilling assembly including drill pipe one end of which is connected to HWDP, downhole drilling motor installed on drill pipe, drill bit arranged on the other end of drill pipe and operating from downhole drilling motor. Secondary drill assembly is arranged inside HWDP with possibility of being arranged between the first position when drill bit is left within the limits of window and the second position when drill bit protrudes sideward from the window provided in HWDP wall. Borehole sinking method by using drill device, during which there performed is the main hole, arrangement of drill device at the specified depth in the main hole, opening of secondary assembly; at that, drill bit leaves the first position and is sunken into the formation enveloping the main hole and drills the secondary offshoot with further return of secondary assembly to the second position.
EFFECT: effective drilling of offshoots without interruption of work in order to arrange small bottom hole assembly.
41 cl, 19 dwg
