M. V. Dvoynikov, D. O. Morozov
For drilling oil and gas wells, screw downhole motors – also known as positive displacement motors (PDMs) – are widely used both in Russia and abroad, accounting for over 80% of applications. However, PDMs exhibit a number of drawbacks affecting the efficiency of directional and overall drilling. First, harmful dynamic phenomena are generated in the motor’s power section, which adversely impact drilling performance. Second, the low output shaft speed prevents the use of certain diamond/PDC bits. Third, the ratio of horizontal reach to true vertical depth almost never exceeds 4.0, whereas with rotary steerable systems (RSS) it can reach 6.0. At present, both motorized and non-motorized RSS are being used with increasing frequency to drill wells with greater departure from vertical and precisely prescribed trajectory profiles at maximum step-out. It is known that each of these and other solutions has its own advantages and limitations that are difficult, and sometimes impossible, to eliminate during drilling operations. A drilling technology employing a two-section PDM with a bi-rotary mechanism is proposed to increase the efficiency of directional drilling. This work presents prototypes of the developed motor, identifies its characteristic similarities and differences relative to earlier tools and technologies, and determines the power-performance characteristics of the two-section PDM – namely torque, rotational speed, power at the bit, and the axial load generated within the bottomhole assembly. The feasibility of the regulating motor operation by adjusting the drilling fluid (DF) flow rate to the power section is substantiated. Potential topics for future research are outlined.