Vibration induced impact damage can significantly reduce PDC bit/cutter life in hard/abrasive and interbedded formations. To develop a more stable fixed cutter bit for these difficult lithologies, an R&D initiative was launched to investigate new cutter designs and experiment with their count/placement to improve drilling efficiency and mitigate vibration. The research yielded an innovative cutting structure and a conical shaped polycrystalline diamond element (CDE) with an ultra-thick synthetic diamond layer.The element is positioned at bit center with the conical tip pointing vertically down towards the rock. The location of the conical element combined with the optimized placement of the conventional PDC cutters allows an uncut rock column to develop. The stress relieved rock column is continuously crushed by the centrally positioned conical element. This enables the bit to deliver faster ROP and reduce the potential for vibration.The conical element has undergone extensive laboratory testing to evaluate its potential to improve ROP. Using a single cutter test apparatus, engineers measured the element's ability to fracture rock at varying depths-of-cut. They determined the new CDE exhibits up to a 70% increase in cutting efficiency compared to standard PDC cutters. An existing PDC bit was modified to include the new CDE at bit center. A Mi616 type bit was fitted with CDE and run in North Dakota and Utah through a highly mixed sequence of formations, where the objective was to increase ROP and to reach KOP in one run. The bit improved ROP over a longer interval drilled compared to benchmark PDCs used in offsets. Subsequent field testing has substantiated the CDE's potential and how it can be used to improve PDC bit performance.

Developing reserves in Kazakhstan's Chinarevskoe field frequently requires the operator to drill an 8.5-in. vertical hole section through extremely hard carbonates which contain high concentrations of problematic chert inclusions. The first significant chert layer is encountered at 3050-3110m, which has 10-50% chert content. Penetrating the chert interval with PDC bits has been challenging and in many cases impossible due to the cutters' inability to withstand high impact forces, which resulted in catastrophic cutter damage. The application of impregnated bits on high-speed turbines (1300-1400 RPM) led to significant improvement in run lengths and this BHA became the standard approach. 1 One impregnated bit could drill approximately 550m at 3.4m/hr. The hole section typically requires three bits to reach TD.However, the impregnated bit generated very small cuttings and high frictional heat altered chip appearance hampering lithology characterization and efforts to identify formation properties. Additionally, the centrifuge was unable to separate the extremely small cuttings from the drilling fluid, resulting in a gradual increase in mud weight over the interval creating the need for constant mud replacement.Tests with PDC were once again attempted, but when the bit encountered a high percentage chert interval, the bits were damaged and pulled in poor dull condition (7-6-CR). After repeated attempts with PDC, the operator realized wellbore verticality was compromised, which required correction run with impreg/turbine BHA with not optimum parameters leading to extra drilling time. The drilling team conceded the chert layers could not be drilled with a conventional PDC/motor BHA. The operator required PDC bit that could efficiently drill long intervals of carbonate formation at high ROP with a durable cutting structure that would remain intact when encountering the chert intervals.To develop a durable bit solution, engineers used an FEA-based modeling system to implement an innovative hybrid-type bit by strategically positioning multiple conical diamond elements (CDE) and conventional PDC cutters across the entire cutting structure from bit center to gauge. This new-style cutting structure leverages the CDE's aggressive shape and superior impact and wear resistance to create a high-efficiency plowing/shearing action that improves performance in difficult formations. The analysis indicated the new hybrid bit would improve performance and be capable of surviving shock and vibration while drilling the hard carbonate/chert formations.The CDE bit was field tested on rotary steerable BHA and drilled 615m at an ROP of 9.1m/hr through the carbonate formation that contained 10-40% chert inclusions throughout the entire interval. Compared to offsets drilled with an impreg/turbine BHA, the CDE bit drilled 12% more meters at 166% higher ROP while providing good wellbore quality and came out with excellent dull condition (1-1-CT). The bit generated much larger cuttings enabling wellsite geologists to readily identify lithology t...

Developing reserves in the northern portion of Russia's Perm region frequently requires the operator to drill extremely hard carbonates which contain high concentrations of problematic chert inclusions. Drilling the chert with PDC bits has been challenging and in many cases impossible due to the cutters' inability to withstand high impact forces which resulted in severe cutter damage. Both rotary and motor BHAs have been utilized in an attempt to mitigate shock and vibration. Rollercone TCI bits are a viable option but slow ROP and short runs combined with high total bit revolutions caused numerous trips for tool change out. It was evident that PDC's shearing action was the most efficient rock failure mechanism and had the greatest potential to drill extended meters at higher ROP compared to a roller cone's crushing action. The operator required a new type PDC bit that could efficiently drill long intervals of carbonate/chert formation at high ROP and a cutting structure that would remain intact when encountering the chert intervals. To develop a durable bit solution, engineers used an FEA-based modeling system to implement an innovative hybrid-type bit by strategically positioning multiple conical diamond elements (CDE) and conventional PDC cutters across the entire cutting structure from bit center to gauge. This new-style cutting structure leverages the CDE's aggressive shape and superior impact and wear resistance to create a high-efficiency plowing/shearing action that improves performance in difficult formations. The analysis indicated the new hybrid bit would improve performance and be capable of surviving shock and vibration while drilling the hard carbonate/chert formations. The hybrid CDE bit was tested and compared against two direct offsets in Russia's North Perm Unvinskoe field. Unvinskoe field was selected for the case study because the formations and application challenges are similar to several other northern Perm fields. The first well was drilled entirely with roller cones which required 10 runs delivering average meterage of 149/bit at an average ROP of 6.05 m/hr. The second well required three roller cones and three 913-standard type PDC bits delivering average meterage of 213.4/bit at an average ROP of 9.65 m/hr. The third well was drilled with one roller cone, one standard PDC with averages of 336m at 8.2 m/hr and two hybrid CDE bits with averages of 433m at 15.6 m/hr. Performance improvement for the CDE bit runs versus offsets runs in wells were: 1) Well-1 190% more meters, 157% faster ROP; 2) Well-2 103% more meters, 62% faster ROP; 3) Well-3 29% more meters, 90% faster ROP.

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An innovative hybrid bit design has been successfully applied offshore Brazil to mitigate geological/formation uncertainties in pre-salt formations and eliminate several trips for new bits. In the application, PDC bits can drill these carbonates effectively until the cutters are damaged by problematic chert inclusions. The hybrid bit is capable of similar ROP and run lengths as standard PDC and allows the operator to achieve a long run at high ROP when no silicate inclusions are present. However, the hybrid bit also provides the added benefit of continued drilling at reasonable ROP when a nodule is encountered with its secondary and tertiary cutting elements. The unique hybrid design utilizes grit hot-pressed inserts combined with alternating PDC shearing elements and wedge shaped TSPs all set in an impregnated post-on-blade design. Extended bit life is achieved when the cutting mechanism changes from shearing to grinding as the PDC/TSP elements are worn away. When the PDC cutting structure is worn down to 50%, the bit still has 75% of life remaining. The paper will focus on case studies where pre-salt carbonate lithology is non-uniform with a high occurrence of silicate inclusions. The authors will discuss drive system and drilling parameters selection that were critical to achieving the desired performance. When used with the appropriate BHA and drilling parameters, the hybrid bit displayed good ROP performance and total footage capabilities. Lower cost/meter was achieved because the hybrid bit had faster initial ROP compared to PDC and stayed on bottom drilling longer due to improved durability with TSP then impregnated cutting structures. Cuttings size and resulting lithology analysis will also be discussed. Engineers are currently working on a real-time surface/downhole data processing system to detect when the impregnated cutting structure engages formation in order to make changes in operating parameters to maximize drilling efficiency and penetration rates.