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The importance of wellbore deviation is well recognized by the drilling industry. An analysis of a drilling system's directional behavior must include the directional characteristics of the drill bit. This paper presents a comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits, including the effect of bit profile, gauge cutters, and gauge length. Numerical simulations as well as laboratory tests have been carried out to better understand the mechanisms of PDC bit deviation and to evaluate the most important parameters affecting the directional behavior of PDC bits. The analysis presented in this paper shows that each part of the PDC bit (profile and active and passive gauges) plays a major role in its walking tendency and steerability. A quantitative evaluation of how these factors contribute to well trajectory (inclination and azimuth) is given. For the first time, a full-scale directional-drilling bench was built to measure the walking tendency and steerability of PDC bits. The results obtained demonstrate that the bit profile, gauge cutters, and gauge length have a significant effect. A 3D theoretical rockbit interaction model was developed to reproduce the drilling test results.

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The importance of wellbore deviation is well recognized by the drilling industry. An analysis of the directional behaviour of a drilling system must include the directional characteristics of the drilling bit. A comprehensive analysis of the directional behaviour of PDC bits is presented in this paper, including the effect of bit profile, gage cutters and gage length. Numerical simulations as well as laboratory tests have been carried out in order to better understand the mechanisms of PDC bits deviation and to evaluate the most important parameters affecting the directional behaviour of PDC Bits. The analysis of the directional behaviour of PDC bits presented in this paper shows that each part of the PDC bit (bit profile, active and passive gages) plays a major role on the walking tendency and steerability of the bit. A quantitative evaluation of the contribution of these factors on the well trajectory (inclination and azimuth) is given. A full-scale directional drilling bench was built to measure, for the first time, the walking tendency and the steerability of PDC bits. The results obtained demonstrate that the bit profile, the gage cutters and the gage length have a significant effect on the walking tendency and on the steerability of the PDC bits. A 3D theoretical rock-bit interaction model was developed to reproduce the drilling tests results. Introduction The oil and gas industry relies greatly on directional drilling to develop petroleum reserves in environmentally sensitive areas or in restricted surface areas through an increasing number of multilateral, horizontal and extended reach wells. To drill and control the deviation of these becoming more complex wells, many directional systems can be used. Depending on the well characteristics, one can select a rotary Bottom Hole Assembly, a steerable mud motor or more recently a Rotary Steerable System. Whatever the system used, the drill bit has an influence on the directional behaviour of the drilling system. This paper enables to define the contribution of the different parts of the PDC bit on its directional behavior (steerability and walking tendency) and their impact on the well trajectory.