Development of a New Concept of Steerable PDC Bit for Directional Drilling

Abstract

Abstract This paper describes the development of a new range of Polycrystalline Diamond Compact (PDC) bits designed to have the smooth torque response of a roller cone bit but maintain the high penetration rates and long life achievable from a PDC bit. One such design features a 360° full contact gauge ring that prevents outer cutters from biting into the formation at gauge. This restriction to lateral movement reduces bit whirl and thereby increases cutting structure life. Thus because the bit drills more smoothly, torque fluctuations are lower resulting in a smoother bore hole which provides more predictable weight transfer. These advantages result in faster penetration rates when sliding because far less time is spent orienting the bit. Laboratory tests utilized an instrumented sub to measure bit vibration as well as weight on bit (WOB), torque and revolutions per minute (RPM). The stability of several bit designs having identical cutting structures but varying degrees of junk slot enclosure was compared. The results show the use of enclosed junk slots significantly reduced bit vibration and gave a much smoother torque response. Several case studies are presented that illustrate improvements in the most demanding directional wells. These bits have now been used successfully on many directional wells in the North Sea, United states and Middle East. Directional drillers have commented that these innovative bits give the directional response and low reactive torque of a rock bit but with three times the penetration rates.