With the development in drilling technology, operators are now drilling further into unknown temperature and pressure regimes, extending the typical well depth to limits never seen before. To deal with these unseen depths, wellbores are being re-designed with more casing strings. Consequently, under-reamers are being used much more frequently to help achieve the optimum hole size for casing.

In bottomhole assemblies (BHAs) with under-reamers it is not unusual to have two neutral points in the assembly, creating a transition zone between both neutral points. To comprehend the effects of placing a reamer in this transition zone, some field cases with reamers placed in this zone were studied. Based on the findings, the reaming bottomhole assembly was optimized to eliminate dual neutral points, which resulted in extended under-reamer life.

This paper discusses the benefits of optimizing hole-opener placement in regards to neutral points and the transition zone. Some precautionary procedures are mentioned that can be implemented to optimize bottomhole assemblies that include reamers, reduce BHA failures and improve drilling efficiency.

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