New Nozzle Hydraulics Increase ROP for PDC and Rock Bits

Abstract The use in drill bits of individual asymmetric nozzles, with special interior transitional surfaces, significantly improves the rate of penetration (ROP) compared to that achieved with conventional circular nozzles. The new fluted nozzles change the pressure distribution and turbulence of the flow. The studies of these new nozzle designs have included controlled drilling laboratory tests, actual horizontal and vertical field wells, computational fluid dynamics models, and flow visualization tests. Drilling results for both polycrystalline diamond compact (PDC) bits and rock bits are given to verify a significant increase in ROP. The fluid mechanics concepts employed are discussed and other validation efforts are outlined. Introduction A new technology for improving drill bit nozzle hydraulics has been developed and is being successfully applied to both polycrystalline diamond compact (PDC) bits and rock bits. The goal of that technology is to use individual asymmetric nozzles in drill bits so as to improve penetration rates in oil and gas drilling by at least 20% over the rates achieved with conventional circular nozzles. Several researcher groups had concentrated on trying to improve the hydraulics of drill bit nozzles, or jets. Some early enhanced nozzle designs were based on using cavitating or resonating fluids but they required conditions that could not be maintained in an actual field environment. Some recent nozzle designs tried to produce swirling flows with several converging small diameter tubes inside the nozzle, or by placing small guide vanes inside the nozzle. But these, and other, methods have not been consistently successful in actually drilling wells. The Vortexx Group Incorporated (VGI) chose a different approach and employed a unique interior nozzle geometric transition shape, and basic fluid mechanics concepts to develop a negative impingement pressure nozzle that also increases turbulence. This behavior is quite different from the standard circular axisymmetric nozzle which is well known to produce only regions of positive impingement pressure on the surface. In some applications the nozzle actually causes a suction (negative pressure) at the impingement surface. For subterranean drilling it decreases the impingement surface pressure to less than hydrostatic. Verification of the negative impingement pressure phenomenon was first obtained, with water, in controlled laboratory pressure measurement and flow visualization tests. Those data were then confirmed by detailed computational fluid dynamics (CFD) studies. The "fluted nozzles" have been shown to have the additional benefit of causing a factor of four or five increase in the volume of fluid that is entrained or drawn into the jet. That causes much more fluid recirculation around the face of the bit and the opposing rock face. Also, the peak turbulence levels increase significantly around the jet. Drilling Laboratory Tests PDC and rock bit rate of penetration tests were conducted with existing bit designs at the Amoco Drilling Research Laboratory (ADRL), Tulsa, Oklahoma in February 1996. The intent of those tests was to vary only the weight on bit (WOB) and the choice of nozzles to determine their effects on the rate of penetration in Cattusa Shale. A 6 7/8 inch (175 mm) Diamond Products International (DPI) TD290H PDC bit was run with a flow rate of about 296 gal/min (1,120 l/min) and a WOB ranging from 3,000 to 13,000 pounds (1,361 to 5,897 kg). A standard 12/32 inch (9.5 mm) diameter circular nozzle was tested against a fluted model V12VLAE. P. 69