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.
Operators of Gulf of Mexico (GOM) wells frequently reported overtorque issue of bottomhole assembly (BHA) connections when drilling the 26-in. section through salt. Such overtorque often leads to costly tool damage beyond repair (DBR), additional trips, and high nonproductive time (NPT). The average DBR cost per BHA can be as high as USD 1 million. Combined with a complete BHA roundtrip, it can easily cost more than USD 3 million for operators if such failure happens. This has been a problem for several years and has caused significant damage: In 2014, of 15 26-in. PDC bit runs in salt, 40% had overtorque connections and 20% led to DBR. This paper discusses how an integrated multidisciplinary team identified the root cause of and the solution to the overtorque problem. Torsional vibration was believed to be the cause of such failure. Comprehensive drilling dynamics simulation software that is based on empirical bit design knowledge was used to design a new bit to reduce the vibration. A newly developed high frequency downhole recording tool used in the 26-in. section recorded high-frequency torque, acceleration, and RPM fluctuation downhole. This dataset became the key to understanding the downhole vibration in detail because it provided information that cannot be acquired by a traditional MWD tool. Field-recorded data were fed into drilling dynamics simulations to accurately calibrate the drilling dynamics model. The simulations resembled downhole drilling conditions and clearly identified the root cause. The simulations precisely predicted the torque along the entire drillstring and identified why overtorque is present in only a certain part of the drillstring. The calibrated model was used to compare old and new bit designs. The newly designed bit showed much lower torque amplitude with similar torsional vibration frequencies. The simulation indicated that the newly designed bit can significantly alleviate the overtorque issue. Implementation of the new bit mitigated the overtorque issue immediately. As of May 2016, there have been 18 runs with the new bit. Only one run had a slight overtorque issue whereas the rest showed no sign of overtorque connections. DBR and NPT related to overtorque were eliminated. As a byproduct, the average on-bottom rate of penetration increased by 9%. This case demonstrates the effectiveness of the integrated approach to solving drilling challenges.
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.
Drilling the hard, abrasive and interbedded Travis Peak and Cotton Valley formations in East Texas creates a difficult challenge for polycrystalline diamond compact (PDC) bits. Historically, conventional PDC cutting elements dulled quickly due to abrasive wear, impact damage and thermal fatigue. Thus, cutter technology has been the limiting factor for efficient PDC bit drilling in the East Texas Basin.Recent technological developments have produced a new, highly abrasion resistant cutter that has increased rate of penetration (ROP) and total footage drilled in addition to producing better dull grades. Further, the sections that normally require two/three PDC bits can now be drilled in one fast PDC bit run. The new cutter technology is designed and manufactured utilizing an innovative process which delivers superior properties both in laboratory testing and field trials. The manufacturing process involves a two-step high pressure/high temperature (HPHT) technique. The first step is to make a polycrystalline diamond table (PCD) using conventional HPHT parameters. The second step is to re-attach the PCD synthetic diamond wafer on a new tungsten carbide (WC) substrate under extreme HPHT parameters. The advantages of this method compared to the conventional one-step process are as follows:1. The residual stress in the PCD table is reduced by the additional second process 2. The two-step HTHP process increases the microstructure strength of the PCD Laboratory tests have indicated the new type of PDC cutter has increased resistance to abrasive wear and thermal fatigue by approximately 100% over standard PDC cutters while not compromising impact resistance. Extensive field tests in the East Texas Basin have documented that drilling efficiency could be improved by 20% in the hard/abrasive application. The cutters are expected to have a positive economic impact on other hard/abrasive applications worldwide.
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