Novel Gauge Extension Optimizes Conventional Drill Bits for Superior Performance with Rotary Steerable Systems

Abstract

Bit gauge length has been a hot topic for several years, particularly when assessing optimal length for rotary steerable systems (RSS). Discussion has not just been about the length; aspects such as geometry, tapering, width, cutting elements, have all complicated the matter further, as well as the fact that different RSS tools require different configurations for optimal balance between steerability, stability, durability, and drillability. This paper describes a joint engineering approach in identifying gauge configurations for the latest generation of RSS that utilizes point-the-bit technology. The project included systematic testing at a purpose-built, full-size drilling test facility. This has enabled a direct comparison of the directional response, hole quality and drill string vibration to be made for the various gauge configurations tested. The testing included use of a novel gauge extension stabilizer. This unique stabilizer provides a method of extending the gauge length of the bit on the rig floor, giving a wider variety of bit selection choices for specific applications. The gauge geometry of the stabilizer provides a 360 º continuous circumferential contact with the borehole, thus providing improved borehole quality and reducing vibration. Field trials proved that the addition of a gauge extender to a short gauge bit can dramatically improve hole quality when used with point-the-bit RSS. The closer gauge hole significantly reduced the severity of downhole vibration and backward whirl. Concerns over lack of steerability, in conjunction with high levels of stick slip and torque, proved unfounded. This study proves that a short gauge, short length bit, when combined with a gauge extender, can be a suitable replacement for a long gauge bit; affording the improved lateral stability required by the RSS whilst allowing operators the freedom to select a widely available short gauge bit with the correct cutting structure.