“…Often, their drivage is accompanied by emergency situations and failures. Amidst them, there are -loss of the bending stability of the drill string under action of gravity forces, torque, inertia forces of rotary motion, etc [1,6,9,10,13,15,17,20]; -self-excitation of torsion autovibration of the drill bit accompanied by alternation of its fast and slow motions [2,4,7,8,11,19,22]; -generation of whirling vibration of the bit connected with instability of the whole system and transition of the bit motion from the regime of pure spinning to its rolling on the bore-hole bottom [5,18,21]; -locking up and sticking of the drill strings in the zones of the bore-holes with enlarged contact and friction forces [3,12,14,16,23]. But the drivage of curvilinear bore-holes is fraught with great technological difficulties caused by permanent balance change of the forces of gravity, resistance (friction), inertia, and elasticity acting on the drill string and its bit.…”