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.

Downhole drilling tools1,2, continue to see improvements in reliability, leading to extended mean times between failures (MTBF). Drive systems, specifically positive displacement motors (PDM), rotary steerable tools (RSS), and turbines have seen extensive improvements in MTBF. Consequently, technical successes on directional drilling programs, where such drive systems are commonly used have also improved. However, these gains do not always translate into meaningful operational success4, which is needed to drive down drilling costs. This situation is caused by some of the industry's perceptions and approach to drilling system design. Additionally, it is influenced by how projects are analyzed, and sometimes interpreted, with regards to performance drilling expectations. This paper will discuss three types of success – technical, mechanical, and operational. It will also identify and discuss the reasons why gaps still exist between technical and operational success. In addition, evaluation processes developed to bridge the gap between technical and operational success will be discussed. Multiple case histories, highlighting the impact of the concepts and evaluation processes to be discussed in the paper, will be presented.