Conical Diamond Element Bit Sets New Performance Benchmarks Drilling Extremely Hard Carbonate/Chert Formations, Perm Region Russia

Abstract

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.

Raiders of the Lost Mud: the geology behind drilling incidents within the Balder Formation around the Corona Ridge, West of Shetland

“…and moderately hard lithologies (such as sandstone and limestone) (Warren 1987). Fixed cutter bits, such as Polycrystalline Diamond Compacts (PDC), are typically more expensive than roller cones, though have more durable wear and therefore are more effective in very hard and abrasive formations such as chert (German et al 2015) and crystalline volcanic rocks (Grindhaug 2012). Hybrid bits are used to drill an interbedded succession of very hard (e.g.…”

Numerical Simulation Research on Cutting Rock with a PDC Cutter Assisted by an Impact Force

“…ey found that when the inclination angle is 20-25 °, the cutting force and specific energy are the minimum, and the crushing efficiency is at the highest. Azar et al and German et al [3,8] applied the hybrid bit in high hardness carbonate rock formation, the footage increased by 29%-190%, the ROP increased by 62%-157%, and the weight on bit decreased by 26%. Conical bit and hybrid bit have great potential and application prospects in prolonging bit life and improving ROP.…”