Drilling the 12 ?" and 8 ?" sections in offshore Abu Dhabi'sDeep Khuff fields is very challenging due to an intricategeological sequence that consists of limestone, dolomite andshales that are highly interbedded with hard stringers.Historically, ADMA-OPCO, the operator, has attempted toefficiently drill the section using roller cone tungsten carbideinserts (TCI), natural diamond and polycrystalline diamondcompact (PDC) technology.PDC bits yielded better performance in terms of rate ofpenetration (ROP) and bit life over TCI bits. However, itrequired several PDC bits to drill the sections. Further detailedanalysis produced optimum PDC designs that successfullyestablished new benchmarks in the fields.The objective was to minimize the number of bit trips byenhancing PDC bits performance. This called for new PDCtechnology coupled with optimized motor drive. To addressthis challenge, ADMA-OPCO and bit vendor and other servicecompanies worked together to seek optimized solutions to drillthe interbedded rocks efficiently.This paper reviews the findings of the detailed study indrilling the 12 ?" and 8 ?" sections in typical Deep Khuffwells. The study showed that PDC damage from encounteringharder stringers was the primary impediment to achievingbetter performance. Subsequent to the recommendations, thechallenges were overcome by utilizing new PDC cuttingstructure designs and advanced cutter technology along withoptimized downhole motor assemblies. The resultantimprovement is also demonstrated by examples from separatefields offshore Abu Dhabi where considerable savings wereachieved in terms of footage drilled and cost per foot.
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