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Influence of bit size on stability bottom drill column balance when drilling a horizontal well

The article raises the question that if you change the bit type, the "critical length" of the lower part of the drill string change too. For the first time, the issue of the stability of the lower part of the drill string when drilling a horizontal section of the wellbore was formulated and solved, taking into account the features of the bit designs (roller bit, wing bit, PDC bit) and the mechanism of rock destruction in well drilling. The research uses the generally accepted provisions of the linear theory of elasticity of materials, the theory of stability of rods and shells. It is assumed that the lower part of the drill string is a heavy elastic rod, experiencing the combined action of the forces of the pipe's own weight and the axial load on the bit, and the twisting moment from the rotor table acting on the pipe string is not taken into account. To find the "critical length" of the lower part of the drill string, simple approximate formulas are obtained that take into account the bit size, drill collar and axial load.