Hole opening with bit and reamer, continues to receive attention in the drilling industry (Meyer-Heye, et al, 2010), due to the operation's numerous advantages. In comparison to conventional (single diameter) drilling, hole opening bottom hole assemblies (BHAs), are more complicated, in terms of their design and operation. The presence of two cutting tools, bit and reamer, in hole opening BHAs present additional drilling dynamics challenges (Heisig, et al, 1998). As a result of these issues, hole opening applications are commonly plagued by the following shortfalls -shorter BHA runs, excessive vibrations (Fear, et al, 1997), downhole tool failures, poor borehole quality, lower rate of penetration (ROP), and compromised directional performance (Mensa-Wilmot, et al 2014). These challenges, which have drastic negative effects on operational costs, amplify in harsh drilling environments (Mensa-Wilmot, et al, 2001).The above issues must be addressed, to ensure cost trend reversals in hole opening applications. This objective requires solutions that focus on the challenges at their sources of initiation. Most important the solutions must ensure consistent and continuous gains in performance. This paper will present new concepts in hole opening, with regards to project analysis, planning, and execution. The discussions will identify and resolve specific hole opening challenges, with emphasis on harsh environment drilling applications. Field cases with supporting data, highlighting the impact of new solutions on project cost reductions, will also be presented. BackgroundSeveral methods, that use different cutting tools ( Figure 1) and BHAs, currently exist for hole opening operations. The available scenarios have dissimilar attributes, capabilities, and operational efficiencies. Considering the challenges posed by the different options, the bit/reamer strategy (Figure 2) is seen as the most efficient and productive approach. Comparisons and evaluations, upon which these positions are based, have been documented by the industry.

Simultaneous hole opening with bit and reamer, based on acknowledged benefits, has become an drilling industry mainstay. Considering Bottom Hole Assembly (BHA) design and compliance requirements, bit and reamer in BHA, and issues with drilling parameters management, the operation presents severe drilling dynamics challenges. Additionally, several other factors initiate, sustain, and/or amplify dynamic dysfunctions. In their totality, these factors and conditions compromise hole opening efficiency, leading to increased cycle times and higher operational costs. Current hole opening solutions and strategies have yielded inconsistent performances. Consequently, appropriate and effective solutions are needed to address above listed challenges. Data analysis must help identify factors and/or conditions that influence performance. These revelations must drive holistic solution approach for hole opening, that will be more effective at cycle time reduction, leading to project costs reductions. These expectations are only achievable, when appropriate implications are derived from effective interpretations of bit and reamer dulls. This paper will highlight and support these considerations with relevant field data, that focuses on hole opening efficiency factors, particularly dynamic dysfunctions. Cycle time effects and project costs considerations, as they relate to hole opening performance in challenging drilling environments will also be discussed.