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. P. 141

Robustness of round and v-shaped polycrystalline diamond compact (PDC) cutters against mechanical and thermal load was evaluated. Forensic analysis was used to estimate the range of loads and depths-of-cut (DOC) that cause structural overload of PDC cutters. Finite element analyses (FEA) were calibrated against this data and used to estimate the integrity of cutters. Thermal-abrasive wear was tested with single cutter tests on Sierra White granite with and without cooling for multiple material grades. The axial and tangential impact resistance were evaluated with drop and front face impact tests. In addition, full-scale lab drilling tests were conducted in granite (UCS=28,000 psi) and quartzite (UCS=56,000 psi). Finally, failures for round and v-shaped cutters were evaluated in field trials. The v-shaped cutters scored similar to baseline cutters in thermal-abrasive tests, but lower in axial impact tests. They also failed at 13-18% lesser tangential load. By accounting for 16% reduction in contact area between the shaped cutter and load anvil, it was concluded that both cutter geometries fail essentially at the same stress. In all full-scale tests, round cutters failed before the shaped cutters. This was in contrast with drop tests and is attributed to the shaped cutter's cutting efficiency, resulting in lesser load on the cutters for the same ROP. The results were then compared with field runs in hard and interbedded application in Oklahoma and West Texas. The conclusion based on FEA, lab, and field data was that in a majority of the cases, this shaped cutter shows the same or better dull as its base grade.

PDC drill bit performance has been greatly improved over the past three decades by innovations in bit design and how these designs are applied. The next leap forward is most likely to come from using high-speed, real-time downhole data to optimize the performance of these sophisticated bits on an application-by-application basis. By effectively managing conditions of lateral, axial and torsional acceleration, damage to cutting structures can be minimized for improved penetration rates. Avoiding these damaging vibrations is essential to increasing bit durability and improving overall drilling economics. This paper describes one set of independent drilling optimization results obtained as part of a series of controlled demonstrations of PDC bits. Sandia National Laboratories on behalf of the U. S. Department of Energy (DOE) managed this work. The effort was organized as a Cooperative Research and Development Agreement (CRADA) established between Sandia and four bit manufacturers with DOE funding and in-kind contributions by the industry partners. The goal of this CRADA was to demonstrate drag bit performance in formations with degrees of hardness typical of those encountered while drilling geothermal wells. The test results indicate that the surface weight-on-bit (WOB), revolutions per minute (RPM) and torque readings traditionally used to guide adjustments in the drilling parameters do not always provide the true picture of what is really taking place at the bit. Instead, a holistic approach combining traditional methods of optimization together with high-speed, real-time data enables far better decisions for improving bit performance and avoiding damaging situations that may have otherwise gone unnoticed. Introduction Sandia National Laboratories established a CRADA between four industry partners, including ReedHycalog. The goal of the CRADA was to demonstrate drag bit ROP and durability performance improvements in hard-rock applications. To achieve this objective, ReedHycalog adopted a holistic approach that involved bit modeling analysis and design for maximum durability and dynamic stability of the cutting structure, hydraulic optimization, rock strength analysis, high-performance thermally stable cutter technology and full-scale laboratory testing. The Diagnostics-While-Drilling (DWD) system developed by Sandia National Laboratories was utilized,1,2,3 to support this work and illustrate the optimization of bit performance with real-time decision-making data. The DWD enabled the transmission of real-time data from immediately behind the bit. Data included lateral, axial and angular accelerations, WOB, bit torque, bending, internal and external pressure and temperature, and system diagnostic data. The real-time data was transmitted to the surface via wireline at approximately 200,000 bits per second (BPS), compared to the existing mud pulse telemetry capacity of only 8–16 BPS. It is anticipated that other data links will be made available in the near future including wired pipe.4 Phase 3 Drilling Outline. This final phase of the CRADA project allowed each drill bit manufacturer to demonstrate its "best-effort" bit design. Phases 1 and 2 involved the characterization of performance for a baseline drag bit; initially without real-time, downhole data feedback for drilling control (Phase 1) and later with downhole data feedback (Phase 2) to optimize bit performance with the aid of an experienced drilling engineer.5,6 The data sets from these earlier phases, which contained both surface and downhole information, were provided to each bit company for analysis prior to Phase 3. These earlier phases will not be discussed in detail except for comparison with the final phase of the project.

This paper details the step by step process undertaken by a dedicated focus group established to provide a solution to inconsistent drilling performance with the 16" section in a deep gas field on the Arabian Peninusular. The paper reviews the analysis undertaken as well as focusing on new design concepts and improved technology introduced.Drilling in these deep gas fields, especially the 16" sections has always been a challenge for Polycrystalline Diamond Compact (PDC) drill bits due to the complex lithology that consists of a variety of carbonates with high interfacial severity, followed by a highly abrasive sandstone and dense dolomite formations. Despite improving the ability to consistently drill the 16" sections in a single run over the past few years, the new challenge is to make further improvements to the consistency while at the same time providing further improvements in rate of penetration.

One of the main challenges drilling within the Troll field, offshore Norway is maintaining a high Rate of Penetration (ROP) while drilling through hard calcite cemented stringers (Jones et al. 2008a; Gunderson et al. 2008). The calcite distribution in this field is complex and can be difficult to predict, while it is easy to maintain a high ROP when drilling the sand sections between the stringers. Early wear or damage to the cutting structure limits the bit's ability to apply sufficient point loading to efficiently cut through the calcite and remaining lithologies, so the key aspects in solving this challenge is to retain the sharpness of the Polycrystalline Diamond Compact (PDC) cutters and minimize the risk of impact damage when hitting these thin inter-bedded stringers at high penetration rates. Following an in-depth study of the application, the drill bit design evolved following several iterations that included computational fluid dynamics to optimize fluid impingement angles and reduce fluid induced shear stress on both the bit body and cutter substrates. Torque control components were introduced to improve the design's response to weight-on-bit, minimize stick-slip and improve directional response. Detailed laboratory tests were conducted to investigate a new edge preparation applied to a new thermally stable PDC cutter, and the cutter-rock interaction was modeled to investigate complex wear, involving impact, abrasion and thermal mechanisms, while drilling these highly inter-bedded formations. The results of this research led to new cutter and bit technologies which have proven that the combination of improved thermal resistance and more efficient cutter geometry enables the cutters to stay sharp while drilling through the hardest stringers and maintain greater durability to complete the section. The improved designs have now drilled further and faster than any previous attempts, resulting in significant cost savings for the operator.