1. Drilling Bits A drilling bit is the cutting tool which is made up on the end of the drill string. The bit drills through the rock by scraping, chipping, gouging or grinding the rock at the bottom of the hole. Drilling fluid is circulated through passageways in the bit to remove the drilled cuttings. Revolutionary idea as Howard Hughes’ rotary two cone bit changed the industry PDC cutters developed by General Electric Company in 1973, are one of the advanced technologies used in the drilling industry. Responsible of crushing and breaking the rock formations as it penetrates the different layers of earth’s crust.

2. Type of Drillbits Rotary Drilling bits usually are classified according to their design as : - Drag Bits, fixed cutter blade (a & b) - Roller Cutter Bits, has two or more cone (c) 2 (a) (b) (c)

3. PDC (polycrystalline diamond compact) bit This type of drill bits includes using diamonds with the bit Today nearly two-thirds of the oil we use comes from wells drilled using the (PDC) bits. APDC bit employs a large number of cutting elements, each called PDC cutter. The PDC cutter is made by bonding a layer of polycrystalline man- made diamond to a cemented Many drill bits include a combination of steel, tungsten-carbide, PDC and diamond cutting and grinding edges. A(PDC) bit employs no moving part and is design to break the rock in shear and not in compression as is done with roller cone bits.

4. PDC Bit design Inserts and cutters Matrix body Matrix is very hard composition contain tungsten carbide grains bonded with a softer and tougher metallic binder. Steel body it is capable of withstanding high impact loads, but is relatively soft and, without protective features, would quickly fail by abrasion and erosion.

5. Polycrystalline diamond compact (PDC) bits a layer of synthetic PDC is bonded to a cemented tungsten carbide, it contains many diamond crystals bonded together. The sintered PDC compact is bonded either to a tungsten carbide bit-body matrix or to a tungsten carbide stud that is mounted in a steel bit. Thermally stable polycrystalline (TSP) bits these bits are manufactured in a similar fashion to PDC bits but are tolerant of much higher temperatures than PDC bits. PDC layers Fig. 3 photograph of PDC cutter

6. PDC tips(Inserts) The fabrication process for PDC tips is similar to that for PDC cutters. The end of PDC tips has a multilayer's structure. The diamond contenting each layer decreases from the polycrystalline diamond layer to the WC-Co substrate they have extremely different thermal expansion coefficients, a residual stresses generated between them. Showed that the multilayer structure has the role of mitigating this residual stress to improve the load- bearing property of PDC tips.

7. PDC cutters PDC cutters are fabricated by sintering a laminate consisting of Co-containing WC powder and artificial diamond particles of 1–10 mm diameter. The sintering conditions are a pressure of 5–6 Gpa and a temperature in the range of 1500–1600 °C, which are similar to the synthesis conditions of artificial diamond. During sintering Co, which acts as a catalyst, is dispersed into the diamond layer

8. The tungsten carbide substrate of a PDC cutter by 1-The substrate acts as a growth platform for the creation of the polycrystalline diamond layer in the HPHT press 2- supplies the needed surface for the mounting of the PDC on a bit head. 3-The substrate also acts as a transition layer between the extremely brittle diamond layer and the significantly less brittle bit body This transition function helps the diamond layer better (absorb impact loads)

9. microstructure effect fatigue threshold test Force & Stress 28.5 kN (2.75 GPa) and 31.5 kN (3.04 GPa) for PDC-A and PDC-B, respectively. single impact to failure. This is about 54 kN for PDC-A and 58 kN for PDC-B. (FVSC) first visible surface crack,(CG-PCD)crack growth through polycrystalline diamond layer,(CF) catastrophic failure

10. microstructure effect PDC cutters exhibit typical fatigue fracture behavior when subjected to repeated impact loads. The fracture stress decreases with increasing number of loading cycles. PDC-B coarse grain microstructure offer a lot more impact resistance compared to their fine grain. PDC-B cutters showed an impact fatigue fracture resistance of up to 70% better than PDC- A fine cutters. The fatigue endurance limit is also about 10–15% higher than that of PDC-A cutters. PDC –B are likely to perform better in applications where impact loading is the primary consideration. (FVSC) first visible surface crack,(CG-PCD)crack growth through polycrystalline diamond layer,(CF) catastrophic failure

11. Manufacture challenges Substrates are composed of tungsten, carbide and cobalt. Tungsten carbide grades are generally categorized as being tougher when they have a greater cobalt content, and as more abrasion resistant when they have a lower cobalt content And the cobalt adds fracture toughness. PDC cutter manufacturers have typically employed substrates containing a uniform gradation of cobalt in a percentage geared toward balancing fracture toughness and abrasion resistance outer shell (lower percentage of cobalt then the will be more erosion resistant) inner core (higher cobalt content to provide the overall substrate with the requisite fracture toughness required of the drilling PDC. Three possible ways of achieving these substrate properties are being explored, the 1-sintering process(migrating atoms of cobalt from one end of the substrate to the other end while migrating atoms of carbon in the other direction,) 2- imbibitions(allows the cobalt imbibitions material to diffuse into the unmasked areas of the target substrate) 3- high-energy mechanical surface treatment of a tungsten carbide substrate( drives cobalt from the outer treated areas into the core of the substrate ) Another area of improvement of tungsten carbide properties that is being explored is microwave sintering(method include faster sintering speeds and lower costs).

13. PDC Advantage PDC cutters can be categorized by their abrasion resistance (by fine diamond grain size in a well-sintered part) impact resistance (by a coarse grain size in a well-sintered part) thermal abrasion resistance(by additional level of thermal stability) researchers at US Synthetic applied a thermally stable layer to a carbide substrate. To make this cutter type, a thin polycrystalline diamond layer is leached of its cobalt. Then the layer is placed on a carbide substrate and re-pressed in the HPHT press. The process yields a thermally stable layer attached to a carbide substrate. "two-step" process once for its original sintering cycle, and a second time to join the layer to the carbide substrate. Within the three categories above, there are many variants. The applications engineer must select the best cutter for the job, without risking other failure modes and without wasting money depend of The formations and drilling conditions will drive the bit selection PDC cutters can be categorized by their abrasion resistance (by fine diamond grain size in a well-sintered part) impact resistance (by a coarse grain size in a well-sintered part) thermal abrasion resistance(by additional level of thermal stability)

14. IADC classification Developed by International Association of Drilling Contractors it has been representative of drillers since 1940.

15. 15  Tooth Wear/Loss Wear is recorded on a linear scale as a single digit from 0 (no wear) to 8 (no usable cutting structure remaining) Use an IADC PDC Wear Gage for PDC For fixed cutter bits the average amount of wear of each area is recorded, with 2/3 of the radius representing the “Inner rows” and the remaining 1/3 representing the “Outer rows” Drill Bit Grading

16. 16  Dull drill bits are graded after runs according to tooth wear/loss, worn bearings, and gauge wear.

17. 17  bearing wear in the field is difficult since the bit would need to be disassembled for inspection. Often the bearing wear is reported based on the total bit running hours. Thus, a bit expected to have a rotation time of 40 hours but rotated at bottom for 10 hours, would bearing wear is reported as B-2  Gauge wear, This can be determined by using a ring gauge and ruler, the gauge ring is placed around the bit and fitted to one side and the space between the ring and third cone is measured. Usually, a bit which diameter is reduced by 0.5 in. is reported as G-O-4, (0.5 x 8). Letter O is for “out-of-gauge” and letter I is for “in-gauge.”

18. Hybrid drill bits Hybrid drilling technology is a paradigm shift in innovation, a coalescence of roller cone and PDC bits into a single, patented design. The result is a technology designed to exploit the best attributes of each bit type, bridging the gap between them. Has features and advantages over both PDC fixed cutters and roller cones

19. summary  PDC cutter consists of polycrystalline diamond band WC-Co layers. The high toughness WC-Co layer firmly supports the polycrystalline diamond layer and also serves as a brazing surface for attaching the PDC cutter to the bit body  PDC cutters are fabricated by sintering a laminate consisting.?A common configuration is the polycrystalline diamond compact (PDC) drill bit Although a PDC bit is expensive, it can last for several hundred hours and drill more footage than other types.  As excavation rate is directly related to the overall cost, the drag bits using PDC (Polycrystalline Diamond Compact) cutters are really attractive compared to roller cone bits. In fact, PDC bits could drill twice faster and longer than roller bits even in hard formations  The ability of the PDC bits to drill different formations with excellent efficiency was proven to the industry (Millheim, 1986). The main advantages of the PDC bits are:  Longer life (Better wear resistance)  Higher average ROP  Better drilling economics ($ / m)