How the Bit Profile and Gages Affect the Well Trajectory

Abstract

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.

PDC Bits: All Comes from the Cutter/Rock Interaction

“…The bit directional behaviour is controlled by the main following characteristics : the bit sterrability and the walk angle 7 . The bit design for a specific directional application must also take into account the dircetional system used, that plays a major role in the deviation process.…”

“…Steerable PDC bits are generally chosen for "push the bit" rotary steerable systems (RSS), although low steerable PDC bits are prefered for "point the bit" RSS. The walk angle is the angle measured in a plane perpendicular to the bit axis, between the direction of the side force applied to the bit and the direction and the direction of the lateral displacement of the bit 7 . Another critical factor in directional system deviation control is the bit tilt.…”

“…Since their introduction in the 1970's, PDC drill bit performances increase continuously by improving PDC technology 1 , cutting structure 2,3 , dynamic stability 4,5 , hydraulic 6 and steerability 7 to drill more and more smoothly and rapidly. Now, with the development of surface and downhole drilling parameters measurements, real time performance analysis 8 become the key of the future drilling performance improvement.…”

Analysis of Spiraled-Borehole Data by Use of a Novel Directional-Drilling Model

“…• The model is formulated at the length scale of the BHA with the rest of the drillstring accounted for at the upper boundary of the BHA through a force and a moment computed from a torqueand-drag model (Menand et al 2006;Denoel and Detournay 2011). This simplification is derived from the observation that the lateral force and moment at the bit are influenced predominantly by the components of the BHA and the contact points with the borehole that are closest to the bit.…”

“…(An "isotropic" bit would be characterized by g ¼ 1; that is, d is coaxial with the applied force F on the bit.) For PDC bits, the lateral-steering resistance usually ranges between 3 for bits with a short active gauge and 100 for bits with a long passive gauge (Menand et al 2002). The angular-steering resistance, v, is usually one or two orders of magnitude smaller than g.…”