Hard and abrasive formations are commonly found in challenging Middle East reservoir sections. These sections are often drilled with up to 10 bits, driving up drilling costs. Low rate of penetration (ROP) and accelerated cutter wear are the primary failure mechanisms encountered. Conventional drill bits have proven unsuitable and uneconomical. This paper presents the development of a Polycrystalline Diamond Compact (PDC) cutter grade housed in a rotating mechanism that has resulted in ground-breaking drilling efficiencies in these formations.
A comprehensive study investigated the cutter-rock interaction and identified the underlying causes behind the accelerated cutter wear in these hard abrasive formations. Following this, laboratory tests were conducted to replicate the failure modes encountered in the field. Five new PDC cutter grades were developed and tested against the field results. In parallel, critical drill bit design levers such as cutter size, blade count, backrake, and cutter chamfer were field tested to determine the most effective configuration. Finally, the optimal cutter grade and bit design levers were integrated into a rotating cutter mechanism and field tested.
The results of this paper focus on validating the development process of the cutter grades, design levers, and the rotating mechanism, both individually and when all three are integrated into an optimal product. Among the three cutter grades laboratory tested, cutter grade C scored the highest, demonstrating a 35% increase in abrasive strength compared to the baseline cutter grade. Field test results against the baseline design with cutter grade C demonstrated a 156% increase in interval drilled.
The optimal design levers combine a 16-mm cutter size with high backrake. The high backrake maximizes the PDC cutter diamond volume in contact with the formation, while the larger cutter size increases the point loading on the formation, minimizing drilling efficiency loss. A 5.875-in. bit that incorporated the design levers and cutter grade C housed in a rotating mechanism was then field tested. The bit demonstrated a 10% increase in interval drilled compared to the best offset run.
The cumulative impact of these individual enhancements led to a step change in drilling efficiency, reducing bit trips and drilling costs.
A reimagination of a classic drill bit design combined with a unique approach to PDC technology has allowed for a paradigm shift in drill bit durability in hard and abrasive rocks. Several bespoke analyses combined with novel drill bit technologies were developed, deployed, and validated in a new modeling environment. A modern and adaptable design philosophy was validated in challenging reservoir environments across the Arabian Gulf.
