PDC Bit Durability – Defining the Requirements, Vibration Effects, Optimization Medium, Drilling Efficiencies and Influences of Formation Drillability

Abstract

Technological advancements, together with improved selection and application practices, have enhanced Polycrystalline Diamond Compact (PDC) bit performance. In addition to drilling faster, these bits are now drilling longer and extending their application envelopes. However in hard, abrasive and highly heterogeneous formations, PDC bit performance still lacks consistency and must be improved. An important qualifier that needs to be optimized in order to enhance PDC bit performance in the harsh environments listed above is durability. However, the engineering efforts needed to define, quantify and explain the concept of PDC bit durability have been minimal. Current industry methods of improving durability have been very ineffective, because they focus on maximization and are based on "trial and error" processes. These approaches compromise the efficient shearing rock removal mechanism of PDC bits, thus their rate of penetration (ROP). They also neglect the relationships and influences formation drillability and vibration characteristics have on durability. This paper will establish the differences and effects of durability maximization (DM) and optimization (DP) on PDC bit performance. It will establish the necessary medium for durability enhancement, and define the processes necessary for its quantification. The influences that formation drillability and vibration behavior have on durability optimization will also be discussed. Laboratory analysis and field data showing DP's effects on drilling efficiency and operational costs will also be presented. The paper will show how durability optimization enhances PDC bit performance in harsh environments. Background PDC bits, by virtue of their shearing rock dislocation mechanism, drill faster at identical loading conditions when compared to other bit types. Although the effects of this advantage on operational efficiency have clearly been established in the industry1,2, the economic impact is consistent only in soft and medium hard formations. If PDC bits could drill hard, abrasive and heterogeneous formations effectively, especially in larger hole sizes and at great depths while maintaining their ROP superiority, tremendous savings could be realized by operators. To achieve this goal, industry R&D efforts have focused on the development of processes and technologies that will enhance PDC bit performance and economics in harsh environments. The improvements that have been made in PDC bit performance, especially in the soft and medium hard formations can be attributed to several factors. Formation drillability analysis, cutting structure (cutter layout) developments, vibration characterization and PDC cutter technology have played key roles in this regard. PDC bit development and selection has benefited from the clear distinction that has been established between formation hardness and drilling difficulty3. Cutting structures with effective vibration prevention and mitigation characteristics have been developed4,5,6. PDC cutters have been engineered to exhibit superior impact, abrasion, thermal and fatique qualities7,8,9. Although these improvements have been beneficial, they have not been effective at extending the application envelope of PDC bits into harsher environments.

Innovative Product Concepts and Drilling Practices Improve Bit and Reamer Performances in Harsh Drilling Environments

“…For similar spatial clearances, these factors dominate the durability and stability discussions. Durability (Mensa-Wilmot, et al, 2000, Sinor, et al, 1998 has two components -static and dynamic. Bits, due to their developmental freedom with features and technologies, see dynamic durability as the main challenge in hole opening applications.…”

Advanced Cutting Structure Improves PDC Bit Performance in Hard Rock Drilling Environments

“…As such, most of the solutions advocated have not had the desired effects. To address the hard rock applications problem, PDC bit durability 7 -in terms of its definition, optimization and relationship to ROP -must be clearly understood. In addition, technologies and/or processes must be developed that drastically slow down the rate of PDC cutter deterioration.…”

New PDC Bit Technology, Improved Drillability Analysis, and Operational Practices Improve Drilling Performance in Hard and Highly Heterogeneous Applications

“…Although inefficient from an operational standpoint, in terms of resulting penetration rates (ROP), certain design features 5 have sometimes been used to account for formation hardness 6 . These have included small PDC cutters 7 , high blade and cutter counts, as well as high back rake angles.…”