Hard and interbedded formations with conglomerates proved a significant challenge to operator, contractor and Service Company in terms of drilling performance, equipment and tool failure. Fixed cutter bits (polycrystalline diamond compact-PDC) experience severe damage resulting in short distance drilled and trips. Roller cone bit normally drill much slower than a PDC bit. The use of conventional PDC and roller cone bits leads multiple runs and trips, resulting in significant higher cost and rig time. By using the hybrid drill bit which combines fixed-cutter and roller-cone elements, higher penetration rate (ROP) is sustained, drilling distance is increased and vibrations are reduced compared to using only PDC or roller cone bits.

Drilling in Tarim Basin, Northwest China has a similar challenge which is to drill the entire conglomeratic interval with improved ROP and reduced vibration while reducing tools/bit related trips.

This paper describes the detail of the first fixed-cutter and roller-cone hybrid bit trial in the Tarim Basin, Northwest China. Result shows over 150% ROP improvement over the best offset record. Five PDC bits and one roller cone bit were replaced saving 16 rig days. The bit drilled smoothly without severe vibration (torque related) and equipment/tools failure.

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