Session: 11-01-03 Well Drilling Technology

Submission Number: 157480

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

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. Drill bit wear cause a decrease in drilling performance, hence increasing the time required to reach the targeted depth, also more energy is required by a worn cutter to break the rock. Presented work is focussed on understanding the wear of a 35 mm lab scale PDC drill bit used to drill synthetic concrete specimen and granite samples and a field scale, 6-inch diameter PDC drill bit, used to drill a formation with layers of grey and red shales.

Field trials were conducted to compare conventional drilling with p-VARD (passive-Vibrations Assisted Rotary Drilling) assisted drilling. As a part of p-VARD development, wear studies for PDC drill bits were required and non-availability of an appropriate wear measurement technique, prompts the development of discussed technique, as per the experimental requirements. Replicas were casted for individual PDC inserts along with HD pictures to record the wear. A term “Wear percentage” is used, based on IADC dull grading system for PDC bits, defining the recorded wear. A linear relationship between ROP and recorded wear (wear percentage) is observed for conventional drilling. Another term “Wear metric” is used to determine the conditions leading to bit wear. Bit wear escalates transitioning from one formation to another. From the study it is concluded that, p-VARD tool significantly increase ROP without affecting wear rates, under certain drilling conditions.

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. Mathematical model used underestimates the ROP values for the intervals drilled using p-VARD tool, confirming the claims of p-VARD tool, made in related publications and patent. The technique used to record wear is very sensitive and is able to record, slightest wear in lab and field settings. In addition, emphasis is on reducing NPT’s and complexity in reporting the wear.

Lab experiments were performed using concrete analogue samples (UCS 50 MPa) to measure performance gains provided by p-VARD tool. Wear was recorded for conventional drilling and p-VARD use. Little to no wear was observed under lab settings. Full sweep of DOT’s was performed at various flow rates. Further, experiments using granite, were performed to see the effect of wear on performance of PDC drill bits, tests were performed at a constant flow rate and WOB. Drill bit wear was reported, but no visible effect on drilling performance was observed.

For field trials, most PDC bit damage occurred due to bit bounce, bit whirl and stick-slip (due to axial, lateral and torsional vibrations). Downhole sensor-sub used for field trials, recorded these vibrations and effect of p-VARD tool in mitigating these vibrations to an extent is observed. Replication using quantum silicones, for individual PDC cutters and use of HD pictures to record and report wear, provides with a precise, reproducible and quantitative method to study and report wear. For field trials, cone cutters were completely damaged showing catastrophic failure, nose and gauge cutters show more gradual wear. Reason is vibrations and excessive WOB, beyond founder’s point.  Wear measurement technique was successfully used for both lab and field scale tests to record and report the wear. Replication of drill bits not only ease the process of studying the bit profile under a microscope, but also provide with a viable mean to estimate volumetric loss of PDC cutters. For field trials, significant wear was reported, and a decrease in drilling performance was seen accordingly.

Presenting Author: Pushpinder Rana Memorial University of Newfoundland and Labrador

Presenting Author Biography: I am a PhD student of Memorial University of Newfoundland, with a topic of study as: To Study the Wear of Poly-Crystalline Diamond Compact (PDC) drill bits and its Effect on Drilling Performance and the role of Mechanical Impedance of Drill string on Drilling Performance. I did my Masters in Oil and Gas Engineering ( year 2011) from Memorial University. I did my Bachelors as B.Tech, Mechanical Engineering from Punjab Technical University, India (2009).