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.

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:

Drilling the hard, abrasive and interbedded Travis Peak and Cotton Valley formations in East Texas creates a problem for polycrystalline diamond compact (PDC) bits. Historically, conventional PDC cutting elements failed quickly due to formation abrasiveness, impact damage and thermal fatigue. These cutter limitations are the major factor restricting further advancement of PDC drilling in East Texas. New cutter technology and manufacturing processes have yielded a highly abrasion resistant PDC bit enabling faster drilling, increased footage and improved dull condition in the basin. Furthermore, intervals that normally require multiple PDC bits/runs to reach TD are now being drilled in some cases with one bit saving the operator trip time and bit cost. In spite of the advancements the majority of bits were repeatedly lacking favorable dull grades, typically a 1-2-WT or worse. Further improvements were necessary to advance the cutter's abrasion resistance for these applications. To achieve the objective and improve PDC cutter performance to save the operator additional cost, engineers refined and implemented new procedures to increase abrasion resistance. This technology platform used to produce the next generation premium cutters included: Tighter diamond packing Diamond table synthesized under extremely HP/HT for enhanced abrasion resistance Refined post-pressing process to reduce residual stress and improve thermal stability In laboratory experiments, the next generation cutter (O2) has shown a 15% improvement in abrasion resistance in wear index comparisons against the previous generation (O1) premium cutters. The tests were performed on a vertical turret lathe under cooling and non cooling conditions. Field testing of the new cutter was done in limited quantities across East Texas. In these tests the new cutter has achieved an average ROP increase of approximately 15% while producing improved dull bit condition. The next generation O2 cutters are expected to have a positive economic impact in the East Texas region and in other hard and abrasive applications worldwide.

Efficiently drilling the lateral hole section through the abrasive Granite Wash reservoir sands in western Oklahoma and the Texas Panhandle creates a unique challenge. The highly heterogeneous formation was causing inconsistent PDC bit performance while constructing the 6-1/8" horizontal and thus damaging project economics. A study determined that improved ROI could be achieved by extending bit life in areas where poor drilling performance is expected. A detailed forensic analysis showed extensive cutter damage with abrasive wear being the most common dull characteristic. The cutter wear was causing short runs and frequent trips for bit change-out. To solve the problem required a new approach. A fixed PDC element creates an inherent limitation because only a small portion of the cutter contacts formation and as the cutter wears, drilling efficiency declines. The resulting wear flat generates a high degree of frictional heat which breaks the diamond-to-diamond bond leading to accelerated cutter degradation. The situation is exacerbated by difficulty transferring weight-on-bit due to extended length lateral drilling. An R&D 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 several different retention methods and developed a specialized fixed housing which is brazed into the bit blade. The PDC cutter is mounted on a circular shaft and fitted within the housing allowing 360° cutter rotation. The robust system holds the cutter/shaft assembly securely in the housing for superior reliability. The rolling cutter assembly has essentially the same OD as a standard PDC cutter for superior design flexibility and cutter placement options. A new-style 6-1/8" PDC (MSiR613/MSiR713) was manufactured with rolling cutters strategically positioned in the shoulder area. It has been run over 45 times in the Granite Wash formation and is delivering positive results. On a steerable motor, the RC equipped bit has increased total footage, hours on bottom and ROP compared to direct offsets drilled with fixed cutter PDC.

As drilling activity in conventional land-based plays continue to decline, technology focus is shifting to the unconventional shale gas prospects (Haynesville, Marcellus, Eagle Ford). Efficient and repeatable drilling practices, along with costeffective technologies, are paramount to economically exploit the known hydrocarbon reserves because of the large number of horizontal wells required to develop the vast acreage plays. The drilling challenges include high bottom hole temperatures, high mud weights and hole/bit cleaning issues. The key to reducing field development costs and improving project economics is increasing rate of penetration (ROP) in the lateral interval that typically extends 3000 to 6000ft after completing the build section.To solve the penetration rate and hole cleaning challenges, an engineering team analyzed the latest polycrystalline diamond compact (PDC) technologies and best drilling practices to achieve the operator's ROP optimization goals. An FEA-based engineering software system was utilized to predict the dynamic behavior of the bit and BHA components in lithologies comparable to the specific field application. To ensure proper utilization of the available hydraulic energy, engineers used computational fluids dynamics (CFD) to ensure appropriate nozzle placement and orientation to effectively clean the bit face and hole bottom. Conclusions from the dual analysis were instrumental in developing new steel body PDC bit designs specifically engineered for emerging North American shale plays.The new steel body PDC design and the associated bit technologies and updated operating practices have been run in the Bossier City, Louisiana and Tyler, Texas areas with outstanding results. The new PDC technology has increased lateral interval ROP by as much as 80%-100% compared to conventional matrix bodied PDC bits. The authors will present several case studies that document the significant cost savings.