Cherty formations are notoriously challenging for fixed cutter drill bits and present a costly challenge for operators who routinely experience short intervals and numerous trips. The predominant limitation is short bit life due to mechanical failure of the cutters. This paper details how an inter-company collaboration led to the development of a design philosophy and a novel shaped cutter technology that resulted in a step change in drilling efficiency and drilling consistency in chert formations.

A collaboration between companies was initiated that commenced with a comprehensive study into the cutter-rock interaction to identify the failure mechanism of chert. The results of the research were then used to determine the critical design levers required to overcome these challenges, extended bit life and maximize drilling efficiency. Two fixed cutter drill bits in the 6-in. and 8.5-in. hole sizes that incorporated the new design philosophy and shaped cutter technology were designed. These bits were then field tested in the Egypt Gulf of Suez interbedded carbonates application characterized with the presence of dark brown chert.

The new 6-in. and 8.5-in. designs were tested twelve times across four different fields. The runs were then evaluated against durability, rate of penetration (ROP) and cost per foot (CPF) compared to field offsets. In the 6 in. section, the new design drilled the entire section of 3,369-ft that includes 381-ft cherty formation with one bit compared to three bits previously required to drill the same interval. For the same offsets, an improvement of between 50-85% in ROP was achieved. The CPF assessment demonstrated drilling cost reduction between 24-75% across the fields tested. In the 8½ in. section, the new design drilled the entire section of 6,141 ft that includes 296-ft cherty formation with one bit compared to four bits previously required to drill the same interval. ROP wise, an improvement between 59-178% was achieved which corresponded to a CPF reduction of between 41-69% across the fields tested. These field tests demonstrate ground-breaking results in the durability, ROP and CPF performance metrics measured. Furthermore, the number of runs and diverse nature of the fields tested demonstrate the consistency of this new approach to drill cherty formations with full directional control and mitigating downhole vibration severity.

A re-examination of the failure mechanism of chert drilling and the root cause behind drilling deficiencies in cherty applications conducted in a collaborative environment has paved the way for a step change in drilling performance. Novel design philosophies were created, laboratory tested, and field validated for consistency of the trials. As the drilling industry continues to explore unchartered applications to ensures cost efficient solutions is paramount to success

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