Drilling the 12¼" and 8½" sections in offshore Abu Dhabi's Deep Khuff fields is very challenging due to an intricate geological sequence that consists of limestone, dolomite and shales that are highly interbedded with hard stringers. Historically, ADMA-OPCO, the operator, has attempted to efficiently drill the section using roller cone tungsten carbide inserts (TCI), natural diamond and polycrystalline diamond compact (PDC) technology.

PDC bits yielded better performance in terms of rate of penetration (ROP) and bit life over TCI bits. However, it required several PDC bits to drill the sections. Further detailed analysis produced optimum PDC designs that successfully established new benchmarks in the fields.

The objective was to minimize the number of bit trips by enhancing PDC bits performance. This called for new PDC technology coupled with optimized motor drive. To address this challenge, ADMA-OPCO and bit vendor and other service companies worked together to seek optimized solutions to drill the interbedded rocks efficiently.

This paper reviews the findings of the detailed study in drilling the 12¼" and 8½" sections in typical Deep Khuff wells. The study showed that PDC damage from encountering harder stringers was the primary impediment to achieving better performance. Subsequent to the recommendations, the challenges were overcome by utilizing new PDC cutting structure designs and advanced cutter technology along with optimized downhole motor assemblies. The resultant improvement is also demonstrated by examples from separate fields offshore Abu Dhabi where considerable savings were achieved in terms of footage drilled and cost per foot.

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