Most traditional polycrystalline diamond compact (PDC) cutting elements have a flat polycrystalline diamond table at the end of cylindrically shaped tungsten carbide body. During drilling, the flat diamond table engages the formation and shears the rock layer by layer. A new ridge-shaped diamond cutting element (RDE) has a similar cylindrical tungsten carbide base; however, the diamond table is shaped like a saddle with an elongated ridge running through the center of the diamond table and normal to the cutter axis. The intended cutting portion, the "ridge," engages the formation to fracture and shear the rock at the same time. The design intent was to create a unique cutting element that could combine the crush action of a traditional roller cone insert and the shearing action of a conventional PDC cutter. The new cutting elements were tested in the laboratory against standard flat PDC cutters in a rock-cutting evaluation, and later the new elements were applied to PDC bits and run under real drilling conditions. The laboratory rock-scrape tests indicated that the new cutting element not only enables the cutter to efficiently shear formation in the same way as a conventional PDC cutter, but also delivers a crushing action similar to a roller cone insert. Preliminary results indicated a reduction of roughly 40% in both cutting force and vertical force on the new ridged diamond element cutters (RDE) over a conventional PDC cutter. Similar findings were also observed during the rock-shearing test on a vertical turret lathe (VTL). Subsequent field tests in multiple areas in North America have produced faster rates of penetration (ROP) in most of the cases. The trials indicate that the new cutting element is efficient at removing rock, and a bit equipped with these elements requires less mechanical specific energy (MSE) during drilling than does a bit with a conventional PDC cutter. In addition, the reduced cutting forces reduces bit torque and thus improves the drilling tools’ life and the bit directional performance. Field data has proven this technology improves drilling performance in terms of ROP and footage over the current PDC bits fitted with traditional flat PDC cutters.
As-melt and uniaxially deformed melt textured YBCO (123) superconductors have been used to examine the role of dislocations in flux pinning. These superconductors were subjected to a high temperature annealing process. After annealing, the critical current densities (J c) of both as-melt and deformed superconductors are found to have decreased dramatically both in zero field as well as in an applied field of 1.5 T. Furthermore, the distinct characteristic of deformed superconductors, i.e., J c ( H|| c-axis)≈J c ( H|| a-b), has totally disappeared after annealing the samples at 900° C for 48 h in flowing oxygen. Transmission electron microscopy revealed that the high dislocation density normally observed in deformed 123 superconductors has been significantly reduced. In addition, several other microstructural changes were also investigated. These results indicate that the large amount of dislocations generated during the deformation process are effective flux pinning centers in these superconductors. Meanwhile, it is suggested that pinning by stacking faults is magnetically sensitive where the effect is maximum at low fields.
A fixed PDC cutting element creates an inherent limitation because only a small portion of the diamond table contacts formation and as the cutter wears/chips, drilling efficiency declines. It is well documented that wear flats generate a high degree of frictional heat which breaks down the diamond bond and in extreme cases can even convert synthetic diamond back to graphite.To solve the issue a research initiative was launched to investigate different methods to enable a PDC shearing element to fully rotate while drilling to increase overall cutting efficiency and bit life. Engineers investigated different retention methods and cutting structure designs to create the optimal driving force to accomplish the objective. Several designs were implemented that hold the cutter securely in place and allow full cutter rotation. These assemblies were modeled using an FEA-based system and then tested in the laboratory to evaluate function and strength. Experiments confirmed the new rolling cutter (RC) was able to shear an extended section of rock with a consistent force level (lbs). Conversely, the traditional fixed-cutter assembly required steadily increased force to drive the cutter the same distance. Examination of the rolling cutter's dull condition clearly indicated significantly improved durability and cutting efficiency.The recent introduction of a new rolling cutter PDC bit that utilizes the entire 360° of diamond edge has delivered positive results in field trials. Initial testing was targeted at the highly abrasive Granite Wash formation in Western Oklahoma/Texas Panhandle where cutter wear is the predominant failure mechanism. Application challenges include low ROP and premature tripping for a new bit. A six-bladed prototype PDC bit was manufactured with rolling cutters strategically positioned in the shoulder area. The bit was run on a steerable motor through the horizontal interval with good results increasing total footage and ROP capabilities.In the central USA the rolling cutter has been run more than 70 times and has increased average footage totals by 56% compared to 450 offsets drilled with conventional fixed cutter PDC bits from various manufacturers. The authors will present results of field tests and two case studies that document performance improvement in these challenging drilling environments. They will also outline plans for future development.
The dependence of critical current on the deformation kinetics has been examined in melt-textured YBa2Cu3O x superconductors that were subjected to uniaxial high temperature deformation. The J c of the deformed superconductors is found to increase with deformation time at all magnetic field orientations with respect to the a-b plane. The rate of increase in J c is found to subside after 12 h of deformation. The deformation time dependence of J c has been analyzed within the framework of high temperature creep, and is found to be very similar to the deformation time dependence of mechanical strain. The rate of J c increase in the secondary creep stage is found to be significantly higher in the orientation of H//c resulting in a lower anisotropy with increasing deformation time. The J c characteristics suggest that an anisotropic defect structure is created after longer periods of deformation, and that the defects responsible for flux pinning are introduced by thermal activation.
Drilling the hard/abrasive Travis Peak/Hosston and Cotton Valley formations in East Texas/North Louisiana creates a distinctive challenge for polycrystalline diamond compact (PDC) bits. Conventional PDC cutters fail quickly due to abrasive wear/spalling and/or delamination of the diamond table. Most bits are typically pulled in poor dull condition graded 1-2-WT or worse. The situation has caused stagnation in PDC performance and limited additional gains in total footage and rate of penetration (ROP). Recent scientific studies have indicated that thermal fatigue of the diamond table is the main contributing factor leading to cutter failure and is restricting further advancement of PDC drilling in East Texas and other hard and abrasive applications. To improve cutter performance the industry must:
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