The 6" PDC bits application of development wells in the Paris Basin (France) has been carried out for a long time. A long directional 6" section of about 1600 meters composed of chalk, sand, shales, hard limestones, with dolomite and anhydrite stringers is currently drilled. In spite of the good results already obtained, several problems were still remaining, the major one was a hard stringer that could not be drilled by PDC bits and was forcing the operator to pull out or to destroy the PDC bit, beside that, nozzle plugging was very frequent.

An engineering study was performed and the analysis of the problems encountered led to the choice of new PDC bit body profile with new cutting structure and nozzles design. These choices were improved by means of hydraulic tests run in laboratory and specific methods of cutters positioning.

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