The application of hybrid bits saves the operator drilling time by out-drilling conventional roller-cone and fixed-cutter bits in the difficult Marcellus shale surface interval. This interval comprises interbedded sandstone, shale, and siltstone down to 600-1,200 ft. deep. Historically, hammer bits and air have been used to drill the surface interval resulting in high penetration rates. In today's environmentally conscious oil industry, some operators have changed casing profiles to better protect water zones and switched to drilling with mud instead of air. Operators drilling these overbalanced wells typically use conventional roller-cone and fixed-cutter bits depending on the area of the play. The roller-cone bits consistently drill the entire interval, yet achieve slow penetration rates due to the lack of available weight. Fixed-cutter bits have been tested to achieve higher penetration rates. They drill faster than roller-cone bits with the available weight on bit, but are accompanied by dynamic dysfunction that leads to a poor dull condition and seldom complete the entire interval.
Extensive research, testing, and development have produced a hybrid bit combining roller-cone and fixed-cutter elements to address these major challenges. The fixed-cutter elements help provide higher penetration rates with the low available weight on bit. The roller-cone cutting elements help drill through the harder part of the interbedded formation by reducing drilling dysfunctions while maintaining a better dull condition.
This paper is a case study comparing the performance of roller-cone, fixed-cutter, and hybrid bits using field results and drilling data from an operator's Marcellus shale surface interval.