The existence of hard, interbedded formations often prove to be very damaging to conventional polycrystalline diamond compact (PDC) fixed cutter bit designs, and as a result, may require additional trips to replace the bit for insert roller cone or impregnated diamond. This can represent significant additional drilling costs for the operator, equating to very high costs per foot if the remaining section to be drilled is short. The challenge is to maintain a low cost per foot, through the use of a bit design which is both durable enough to drill the desired interval, at the best possible penetration rate. This paper describes the development of a new innovative drill bit technology that fuses two existing fixed cutter materials using a unique design philosophy that allows for greater versatility in drilling a wider range of interbedded, difficult to drill lithologies that are not typically drilled entirely with PDC bits. This novel design philosophy includes optimized cutter placement allowing engineered exposure of diamond impregnated mix applied in critical areas of the bit for added durability. This development project was initially targeted for the sub-Saharan region in the Congo, where the existence of a conglomeratic interval at the bottom of the section prevented to reach total depth (TD) with fixed cutter bits, having to end with roller cone insert designs. In its first trial, the new design drilled three times the interval of the best offset with a 34% improvement in rate of penetration (ROP). Applications in different regions of China were soon identified, resulting in a challenge to design for a new hole size with various drive types; the results of which are detailed in this paper.


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