Investigation of PDC Drill Bit Wear and its Effect on Drilling Performance

Abstract Drill bit wear and damage is a major cause of bit pullout, from the well. This increases Non-Productive Time (NPT) and cost of drilling. Presented work is focussed on the wear investigation of a 6-inch diameter PDC drill bit used for field trials conducted in the year 2014, to compare conventional drilling with p-VARD assisted drilling. A total of 461.8 ft of formation, comprising of alternating layers of red and grey shales is drilled using the bit. A term “Wear percentage” is used, based on IADC dull grading system for PDC bits, representing the recorded wear. Another term “Wear metric” is used based on literature to determine the conditions leading to bit wear. A mathematical model is utilized to better understand the effect of factors like drill bit wear, rock formation strength and its abrasiveness on observed ROP. A linear relationship between ROP and recorded wear is observed for conventional drilling. Mathematical model used underestimates the ROP values for the intervals drilled using p-VARD tool. Cone cutters are completely damaged showing catastrophic failure, nose and gauge cutters show more gradual wear. Study shows no evidence of any effect of p-VARD tool application in increasing wear of PDC drill bit used. Stick-slip and chaotic whirl observed is the reason of the type of wear and severity of wear reported. Vibrations and excessive WOB, beyond founder’s point cause the damage of cone cutters.