The advances of borehole enlargement (BHE) technology have been a game changer for deepwater well construction in the recent years, allowing larger OD casing strings to reach ever-increasing depths. Among the many reasons why this operation might be required, the potential of a geological structure to have hydrocarbon bearing formations from shallow to deeper depths entails different and challenging operational well construction alternatives, each one with its trade offs. It might be the case that in aiming to strike balance between achieving the formation evaluation goals and allowing a feasible and cost effective well construction, a pilot hole and subsequent hole enlargement strategy might be selected.

This paper presents a case study of two consecutive hole enlargement sections (12-1/4″ × 20″ and 12-1/4″ × 17-1/2″) on a deepwater wildcat well offshore South East Asia. Whilst not a novel procedure, performing such operations in a single run to accommodate large casing sizes in deepwater well construction, working from pre-drilled 12-1/4″ pilot holes, is uncommon. Several challenges associated with drilling dynamics, drilling performance, hole quality and barrier integrity were overcome by the application of hole enlargement technology, rigorous planning and operations workflow.

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