An Unconventional Fixed Cutter Cutting Structure Layout to Drill Through Hard, Abrasive Conglomerates in Deep Wells—A Case Study

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Abstract Access to new reservoirs requires drilling at increasingly greater depths through more challenging environments with limited resources. Hard Rock bit cutting structure layout has been developed to extend bit life, drilling through hard, abrasive, and thick conglomerate and sandstone intervals while achieving significant rate of penetration (ROP) improvement. A case study is presented to demonstrate the liability and consistency of this new technology. In Oman, one of the most challenging formations is Amin. It's composed of hard conglomerates, abrasive sandstone, and layers of medium hard shale. The formation thickness is typically 1500 m. Roller cone bits have been used to drill it for years with low performance and high operational risks. Eight to eleven bits were usually required to drill the section at poor ROP. Polycrystalline diamond compact (PDC) bits were also tested previously with limited improvement at poor footage and ROP. An unconventional bit cutting structure layout referred to as multilevel force balancing was used to develop fit-for-purpose designs combined to a new generation of cutters. A comprehensive engineering analysis of bit performance in the area was carried out, including formation strength, bit design details, drive system, and an understanding of drilling parameters. Additionally, the introduction of new materials led to bit design adjustments based on hard rock drilling concepts. The combination of cutter technology and multilevel cutting structure layout was used to create a fixed cutter bit, setting records for drilling hard and abrasive lithology in Oman, delivering more intervals drilled with higher ROPs than the roller cone bits used previously. The bit consumption was reduced to an average of three bits, achieving 75% improvement in terms of footage drilled, and 100% ROP improvement. This new generation of fixed cutter bits has now become the standard for drilling in high interbedded formation as well as hard and abrasive rock formations in Oman. This paper discusses hard and heterogeneous rock drilling challenges and how the hard rock bit technology could help address the lacking conventional drill bit performance. The specialized implementation process and analysis of the technologies are highlighted. Detailed offset data and rock strength analysis are included to support the results achieved.