Drilling the 16" hole section through mostly carbonates in southern Kuwait presents several distinctive challenges. Interbedded formations with vastly different compressive strengths that vary between 5-30 Kpsi and a significant amount of blind drilling can result in twist-off and lost-in-hole situations. The most common tungsten carbide insert (TCI) rollercone bit failures mechanisms are impact induced cutting structure damage, hydraulic inefficiency issues and bearing failure caused by high weight-on-bit (WOB) through the hard Dammam to Ahmadi carbonate sections.

To solve the challenges the operator's drilling team, working in conjunction with the bit supplier, launched a performance improvement initiative. The carbonate application was analyzed using finite element analysis (FEA) based dynamic simulation program to fully understand how to stabilize the bit in different downhole conditions and improve hydraulic efficiency. Based on the computer analysis and field run data, engineers conceived a new stable bit design. The technology platform includes improved hydraulics and a specialized cutter structure configuration with tougher insert carbide grades to mitigate impact damage. A high-aspect ratio seal employs two dynamic sealing surfaces (ID, OD) that reduces frictional heat and minimizes wear to improve bearing reliability.

The new rollercone bit was run with an optimized drilling plan with outstanding results establishing a performance step change in southern Kuwait's carbonate applications. The bit recently set a new 16" world cumulative TCI footage record of 12,656ft drilling three wells shoe to total depth (TD) and 531ft of a fourth well. The bit amassed a total 446 hours of on-bottom drilling time turning 2.4 million revolutions without a seal failure. The bit saved the operator 4.5 days of rig time plus bit spend. The new technology has enabled the operator to drill long footage intervals or multiple wells using a single bit with good penetration rates (ROP). The authors will discuss the formation challenges, application analysis and resulting performance improvement.

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