The application envelopes of PDC bits have conventionally been defined by rock hardness. Although technologies1,2, 3, 4  aimed at improving PDC bit efficiencies in challenging drilling environments continue to be developed, performances in such applications still lack consistency. It has become apparent, from drilling performance evaluations, that formation hardness alone can not be used to categorize PDC bits.

In some instances, PDC bit performances have varied profoundly across given fields, even when formation types and tops, lithologies and hardness have been determined to be comparable. These performance differences, which continue to baffle the industry, amplify with increasing formation heterogeneity especially in hard rock environments.

This paper will present a three part process, which has been developed to address the challenges described above. First a new approach, which characterizes rocks by their drilling difficulty, is used to establish field trends. Considering offsets, or anticipated performance requirements, bit development and/or selection is done with the aid of two new parameters – stress and durability equivalencies. Finally, operational practices aimed at enhancing the effectiveness of this new process are developed and implemented. This paper will quantify and discuss the individual and combined effects of these processes.

Analytical, laboratory and field data, showing the effectiveness of this new methodology, will be presented.

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