Hybrid Drill Bit Combining Fixed-Cutter and Roller-Cone Elements Improves Drilling Performance in Challenging Application in the Western Desert

Abstract

The application of hybrid bits saves the operator drilling time by out-drilling conventional roller-cone and fixed-cutter bits in difficult, dense, tough and interbedded intervals. These intervals comprise interbedded sandstone, limestone, and siltstone down to depth of 12,500 to 13,500 ft. Operators who drilled these overbalanced wells typically used conventional roller-cone and fixed-cutter bits, depending on the area of the play. The roller-cone bits consistently drilled the entire interval, yet achieved 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 with higher drilling torque, close to the rig limitation. Fixed-cutter bits also experience dynamic dysfunctions that prematurely damage the bits, making it difficult to complete the entire interval. Extensive research, testing, and development have produced a hybrid bit that combines roller-cone and fixed-cutter elements to address these major challenges. The fixed-cutter elements make the bit more aggressive and provide higher penetration rates at low weight on bit. The roller-cone cutting elements drill through the harder part of the interbedded formation with much lower torque oscillations, making it easier to achieve the directional requirements, and reduce dynamic dysfunctions, improving the reliability of the bottomhole assembly and a better dull condition of the drill bit. This paper will present analysis of drilling data from the field to provide a detailed description of the operational challenges in this application by comparing the performance of roller-cone, fixed-cutter, and hybrid bits. After describing the planning and operational execution of drilling an 8.5-in. hole section with a hybrid bit in this challenging application, the paper concludes with a discussion of the technical and economical benefits and potential of this new technology.

Working characteristics research on the impacting–cutting hybrid bit

“…Particularly, if the bottom-hole rock is of high hardness or high strength, it is difficult for the PDC cutter to penetrate the rock and complete a valid cutting process, especially when the cutter is worn after a period of drilling, it will be even more difficult for the cutter to penetrate, accordingly, rate of penetration (ROP) of the bit will be significantly lowered. [1][2][3][4] On the other hand, down-the-hole (DTH) hammer bit used in rotary percussive drilling is a fixed-tooth rock-breaking tool without moving parts, which is quite similar to the PDC bit in this aspect. In a DTH hammer bit (hereinafter referred to as hammer bit), a series of teeth or inserts (typically are tungsten carbide inserts) are fixed on the bit body so as to cover the bottom-hole rock that will be removed.…”