Publications

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In order to generate new properties of metals exposed to high pressure states, it is desirable to study samples loaded in one-dimensional strain. Previous work to obtain these ideal conditions, involve a technique where the sample was recovered at late times to examine its microstructure. In those experiments, the shock-loading was produced by impacting the sample with a flyer plate. In the present work, we modified the sample recovery assembly and optimized it for ramp wave loading. We describe the 2-D calculations performed with the ALEGRA MHD code that led to improved recovery assembly efficiency. Preliminary comparisons of the simulations with measurements of the sample deformation from an experiment indicate excellent agreement. © 2009 American Institute of Physics.

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Polycrystalline diamond compact (PDC) bits have gained i wide popularity in the petroleum industry for drilling soft and; moderately firm formations. However, in hard formation applications, the PDC bit still has limitations, even though recent developments in PDC cutter designs and materials steadily imj proves PDC bit performance. The limitations of PDC bits for drilling hard formations is an important technical obstacle that must be overcome before using the PDC bit to develop competii tively priced electricity from enhanced geothermal systems, as well as deep continental gas fields. Enhanced geothermal energy is a very promising source for generating electrical energy and therefore, there is an urgent need to further enhance PDC bit per-j formance in hard formations. In this paper, the cutting efficiency of the PDC bit has been) analyzed based on the development of an analytical single PDC cutter force model. The cutting efficiency of a single PDC cutterj is defined as the ratio of the volume removed by a cutter over the force required to remove that volume of rock. The cutting I efficiency is found to be a function of the back rake angle, the depth of cut and the rock property, such as the angle of internal' friction. The highest cutting efficiency is found to occur at specific back rake angles of the cutter based on the material properties of the rock. The cutting efficiency directly relates to the internal angle of friction of the rock being cut. The results of this analysis can be integrated to study PDC bit performance. It can also provide a guideline to the application' and design of PDC bits for specific rocks.

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Complementary gas-gun and electro-magnetic pulse tests conducted in Sandia's Dynamic Integrated Compression Experimental (DICE) Facility have, respectively, probed the behavior of electronic-grade Kovar samples under controlled impact and intermediate-strain-rate ICE (Isentropic Compression Experiment) loading. In all tests, velocity interferometer (VISAR) diagnostics provided time-resolved measurements of sample response for conditions involving one-dimensional (i:e:, uniaxial strain) compression and release. Wave-profile data from the gas-gun impact experiments have been analyzed to assess the Hugoniot Elastic Limit (HEL), Hugoniot equation of state, spall strength, and high-pressure yield strength of shocked Kovar. The ICE wave-profile data have been interpreted to determine the locus of isentropic stress-strain states generated in Kovar for deformation rates substantially lower than those associated with a shock process. The impact and ICE results have been compared to examine the influence of loading rate on high-pressure strength.

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A series of field tests sponsored by Sandia National Laboratories has simultaneously demonstrated the hard-rock drilling performance of different industry-supplied drag bits as well as Sandia's new Diagnostics-While-Drilling (DWD) system, which features a novel downhole tool that monitors dynamic conditions in close proximity to the bit. Drilling with both conventional and advanced ("best effort") drag bits was conducted at the GTI Catoosa Test Facility (near Tulsa, OK) in a well-characterized lithologic column that features an extended hard-rock interval of Mississippi limestone above a layer of highly abrasive Misener sandstone and an underlying section of hard Arbuckle dolomite. Output from the DWD system was closely observed during drilling and was used to make real-time decisions for adjusting the drilling parameters. This paper summarizes penetration rate and damage results for the various drag bits, shows representative DWD display data, and illustrates the application of these data for optimizing drilling performance and avoiding trouble.

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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.

Sandia National Laboratories has partnered with industry on a multifaceted, baseline experimental study that supports the development of improved drag cutters for advanced drill bits. Different nonstandard cutter lots were produced and subjected to laboratory tests that evaluated the influence of selected design and processing parameters on cutter loads, wear, and durability pertinent to the penetration of hard rock with mechanical properties representative of formations encountered in geothermal or deep oil/gas drilling environments. The focus was on cutters incorporating ultrahard PDC (polycrystalline diamond compact) overlays (i.e., diamond tables) on tungsten-carbide substrates. Parameter variations included changes in cutter geometry, material composition, and processing conditions. Geometric variables were the diamond-table thickness, the cutting-edge profile, and the PDC/substrate interface configuration. Material and processing variables for the diamond table were, respectively, the diamond particle size and the sintering pressure applied during cutter fabrication. Complementary drop-impact, granite-log abrasion, linear cutting-force, and rotary-drilling tests examined the response of cutters from each lot. Substantial changes in behavior were observed from lot to lot, allowing the identification of features contributing major (factor of 10+) improvements in cutting performance for hard-rock applications. Recent field demonstrations highlight the advantages of employing enhanced cutter technology during challenging drilling operations.

Sandia National Laboratories and Security DBS have collaboratively examined the hard-rock drilling performance of a conventional drag-bit design that was run in conjunction with field tests of Sandia's prototype Diagnostics-While- Drilling (DWD) system for acquiring real-time downhole and surface data. This effort constituted the first two phases of work under the terms of a multi-partner Cooperative Research and Development Agreement (CRADA) that has been established between Sandia and four bit manufacturers for the purpose of developing and demonstrating "best effort" drag bits that are capable of drilling difficult formations such as those commonly found at geothermal energy production sites. For both CRADA phases completed to date, the test bit (Security DBS, Model PD 5) drilled in the same well-characterized hard lithologic interval at the GTI Catoosa Test Facility near Tulsa, OK. In each case, extensive time-resolved downhole and surface data were acquired with the DWD system. During Phase 1, an experienced driller controlled the drilling parameters only on the basis of standard rig instrumentation readings. For Phase 2, one or more drilling engineers continuously observed the streaming DWD displays and actively guided the drilling process. Significantly different results were achieved in Phases 1 and 2 for penetration rate and bit life, which are reported along with bit damage assessments and representative data from the unique downhole measurement sub that monitored conditions at the bit. This information has supported the development of designs and DWD-based drilling strategies for the "best effort" bits being tested during CRADA Phase 3.

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