Investigation of PDC diamond drill bit wear and mechanical impedance of drill string, and study of their impact on drilling performance

Polycrystalline Diamond Compact (PDC) drill bit wear is a critical factor influencing drilling efficiency and is a major contributor to Non-Productive Time (NPT) in drilling operations. This study presents a comprehensive PDC bit wear measuring technique, the experimental development and testing of a passive Vibration Assisted Rotary Drilling (p-VARD) tool, and the evaluation of their combined effects on drilling performance in both laboratory and field environments. The intricate shape of PDC cutters, limited availability of bit between drilling runs and weight of PDC drill bit, pose unique challenges for studying bit wear. A wear estimation technique was developed using high-fidelity replicas to quantify and document wear in both lab-scale and field-scale PDC drill bits. The method incorporates visual inspection, weight measurements (for lab-scale bits), and high-resolution imaging. For lab scale PDC drill bit, despite minor edge rounding and minimal shrinkage, the replicas preserved critical surface features, enabling accurate measurement of chamfer width and PDC thickness loss. For field-scale bits, the IADC dull grading system was employed. High Definition (HD) pictures after each drilling run along with localized replicas of worn cutter were used to record and investigate field-scale PDC drill bit wear. This approach offers a permanent and precise record of bit condition. The CERCHAR Abrasiveness Index (CAI) test was examined in detail. The study evaluated the effects of scratch length, styli reuse, and confined stress conditions on CAI results. A linear relationship was observed between applied pressure and CAI, and a correlation was established between CAI and Unconfined Compressive Strength (UCS) for both natural sedimentary rocks and synthetic concrete analogues. Design improvements to the CAI apparatus were proposed and implemented, enhancing test consistency, accuracy and test portability. A lab-scale prototype of the p-VARD tool was successfully developed and tested, leading to the development of a field-scale version compatible with a 6” PDC bit. Field trials, conducted over 461.8 feet of alternating red and grey shale formations, demonstrated a significant increase in Rate of Penetration (ROP) under specific operational conditions. Two metrics were introduced to quantify the wear of 6” PDC drill bit: “wear percentage,” based on IADC dull grading, and “wear metric,” derived from literature to identify wear-inducing conditions. A linear relationship between ROP and recorded wear was observed in conventional drilling, while p-VARD-assisted drilling showed no increase in wear rates over rates observed in conventional drilling. Stick-slip and chaotic whirl were identified as primary contributors to severe wear, particularly when excessive Weight on Bit (WOB) exceeded the bit’s founder point, leading to cutter damage. In conclusion, this work introduces innovative methodologies for wear assessment and vibration-assisted drilling. The replica-based wear estimation technique offers a reliable and scalable solution for both lab and field applications. The p-VARD tool demonstrated promising performance improvements without compromising bit integrity. Additionally, refinements to the CERCHAR test protocol and equipment contribute to more accurate abrasiveness characterization. Collectively, these advancements support the development of more efficient and resilient drilling systems.