Experimental Study of Combined-Jet PDC Bit

In order to apply different jet modes to PDC bits,numerical simulation and laboratory tests had been done to study the bottom-hole flow field affected by reverse jet.Rock breaking ability of swirling jet in the laboratory was evaluated,which could provide basis for bit design.The results showed that obvious pressure declined at rock breaking with backward jet nozzles on PDC.As the distance between reverse jet nozzle outlet and bit bottom decreased,and reverse flow rate increased and the degree of pressure drop increases at bottom holes.The pressure of drilling fluid column pressure had little effect on the pressure drop.Compared with conventional jet,swirling jet had better rock breaking ability at the same pressure drop and flow rate.According to the test results,a new combined-jet PDC bit,joining reverse jet and swirling jet,was developed and used on Well Tuo 747.The test results showed that it could improve ROP by more than 40% compared with the neighboring wells using conventional PDC bits.It was proved that the combination of reverse jet and swirling jet on PDC bit can improve ROP remarkably.