Method of drilling string assembly for secondary opening of a productive formation

A method for drill string assembly as a technical dynamic system of connected oscillators for drilling branched channels of small diameter, including an assembly of operating components of various natural frequency positioned in a dynamically disturbed zone of the loaded part of the drill string,

• wherein
• a drill string assembly (DSA) including oscillators positioned as coupled units, a drill bit, a bearing section of the mud motor, power sections of the mud motor, rigid and coiled tubing assemblies with viscoelastic mechanical properties and different natural frequencies, and an axial load control unit, is mounted on a test bench
• conducting tests following modeled programs of possible emergency and emergency-free operation modes for an assembly as a whole and its individual components,
• measuring amplitude, vibration speed and vibration acceleration for longitudinal, transverse and torsional vibration are measured for drilling each kind of bed rock, trends for cumulative wave motion are obtained for oscillators moving with collective group speed,
• analyzing said obtained values are analyzed to determine areas of dynamic stability at the test bench, displacement amplitude, determining vibration speed and vibration acceleration trends for longitudinal, transverse and torsional oscillations during test bench drilling,
• conducting spectral analysis of the results, obtained by calculating of the spectral density of the operating components within the assembly;
• obtaining operating components trajectories for dynamic disturbance zone of the DSA in the phase plane,
• determining the length of dynamically disturbed zone of the loaded part of a drill string based on the group velocity of the energy propagation for the monochromatic longitudinal, transverse and torsional waves batch, where waves differ in phase and frequency and propagate along the string with prevailing natural frequencies, different phase velocities at linear and nonlinear, stochastic oscillations that appear in the drill string due to running out of the formed “dynamic stability points”,
• additionally, placing an axial thrust control unit in the “dynamic stability points”, adapted to operate at various damping ratios, with its prevailing natural frequency obtained based on statistical processing of the spectral density values and phase trajectories,
• selecting the required mode of operation for the assembly and its operation characteristics:
• natural frequencies considering different bending and torsional rigidity values, damping properties of the axial load control units and their optimum placement.