fax 01-972-952-9435. AbstractThe effects of downhole vibration on drill bit performance have been discussed a great deal in the past several years. Data acquired on near-bit vibration has proved useful for assessing bit selections, design features and running parameters. Typically, engineers have had only limited access to this type of data because measurement-while-drilling (MWD) tools capable of acquiring vibration measurements are generally placed well above the bit in the bottom hole assembly (BHA), where the dynamics can be significantly different than at the bit. Also, these conventional MWD tools are expensive to operate.The recent development of an easy-to-use, memory-mode, vibration-logging tool has made obtaining relevant " at-bit" data much more feasible. The tool is very small and can be used in collar sizes as short as 8 in. from shoulder-to-shoulder. The tool can be placed directly above the bit without disturbing the BHA. This paper highlights the development of this tool and presents data from recent field tests that show how it has been used to optimize and evaluate drill bit performance in various applications.

For years drillers have been taught to mitigate all vibrations in the drillstring while drilling to maximize Rate of Penetration (ROP), limit bit damage, and extend bit life. While limiting lateral vibrations and stick/slip are proven ways to improve performance and maintain directional control, in recent years it has been conclusively proven in the field that inducing axial agitation with specialized downhole tools can significantly improve lateral reach. Currently, however, the benefits of downhole oscillation tools have not been thoroughly studied for other performance gains, such as improved ROP in non-directional wells.An extensive research study, including lab and field testing, found that a low-frequency, benign axial vibration can increase the ROP significantly in all well types. Initial laboratory experiments were performed by inducing axial vibrations into the drilling process on a small scale drill bit in hard rock. Dramatic improvements in ROP and drilling efficiency were observed, with the added benefits of improved bit life and an unexpected reduction in stick/slip. This lab experiment was later tested in the field by utilizing a proven downhole oscillation tool in an active Bottom Hole Assembly (BHA) to create the effect that was simulated in the lab. The field tests showed the same results as the lab tests: significant performance gains were observed in several test wells using the downhole oscillation tool as compared to offset data. In addition, this same downhole oscillation tool showed drastically improved directional control when run above a Rotary Steerable System (RSS) tool, and stick/slip was practically eliminated with no negative effect on bit life or BHA reliability.High-speed sensor data collected at the bit during both the lab and field tests will further demonstrate the validity of the theory. Testing for a hard-rock application with roller cone bits is forthcoming, as the data indicates possible performance gains in this environment as well.Overall, the study revealed many benefits, such as improving well placement, reducing Non-Productive Time (NPT) and time to Total Depth (TD) by preventing BHA component damage through beneficial axial vibrations from the downhole oscillation tool. The data indicates that "benign vibration" can drastically improve drilling performance. Induced Vibration Theory and Application Background (Forster and Grant, 2012)Theoretically, any drilling assembly which provides a fluctuating axial load application focused downhole will improve drilling efficiency. The axial excitation will improve drilling efficiency by breaking static friction, both in the BHA and at the bit. Once static friction is overcome and stead-state dynamic friction results, the Weight on Bit (WOB) required will be a fraction of the WOB required under normal drilling conditions, and load transfer will improve.

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.

A drill bit dynamics sensor system has been developed with a new approach that enables economical, widespread use of downhole data to improve bit design. The system emphasizes ease of deployment and minimal manpower requirements for data interpretation. The goal was to develop a system appropriate for deployment on a new scale to the bit industry. The system consists of a small in-bit sensor coupled with an automated software system that provides direct design guidance targeted at drill bit specialists. This paper aims to detail the design considerations used to develop this system and provide an example application of the technology from field testing.

Local hyperthermia has been the subject of much research because of its great potential for therapeutic and clinic applications. It has been long recognized that a major factor, which affects tissue temperature elevation and heterogeneity during hyperthermia, is the augmentation of blood flow concomitant with the heating. The heat-induced change in local blood flow can be attributed to sympathetically mediated re-distribution of cardiac output and change in local flow resistance resulting from thermally stimulated regulation in diameters of arterioles. It has been found that the vascular endothelium significantly affects the dynamic response of the vessel diameter to thermal stimuli. Endothelial cells play key regulatory roles by producing several potent vasoactive agents and regulating coagulation states, i.e. endothelium derived relaxing factors (EDRFs). Most endothelial functions depend to various extents on changes in intracellular calcium concentration [Ca2+]i. A new approach to studying vascular thermo-regulation during hyperthermia has been developed in this research to quantitatively measure the dynamic response of vascular endothelial Ca2+ to temperature elevations using confocal fluorescence ratio imaging. The cell membrane permeable fluorescence dye Fura-2/AM esters were loaded into the vascular endothelial cells and ratio imaging of the fluorescent endothelial cell were taken under the excitation of 334 and 380nm wavelengths. The signal intensities were calibrated with the endothelial calcium ion concentration ([Ca2+]i) and temperatures ranged from 37°C to 44°C. This calibration will provide a means to quantitatively measure the vascular endothelial [Ca2+]i transients in in vivo tissue when subjected to temperature elevations from 38°C to 44°C, and thus to further understand the role of endothelium in thermally induced vascular regulation under hyperthermic conditions in the near future.