Advanced Hydraulics Analysis Optimizes Performance of Roller Cone Drill Bits

摘要

For nearly 30 years after the introduction of jet bits, all triconebits had virtually identical nozzle systems. Nozzles wereaimed toward the corner of the borehole bottom, more or lessequidistant between the cones. More recently, tricone bitswith unique patented nozzle systems have appeared and todaydrillers can choose between at least five different nozzleconfigurations. It is recognized that cone cleaning nozzlesystems perform best in bit balling environments and boreholecleaning nozzle systems perform best in bottom ballingenvironments. Another characteristic of bit hydraulics, whichhas not received much attention in the literature, is the abilityof a bit to evacuate cuttings. Since one bit may encounter bothbit and bottom balling environments during its life and all bitsmust evacuate cuttings, it is most ideal if one nozzle systemcan be developed which performs well in all three of theseaspects.A bit with a new nozzle system, described in this paper, hasbeen shown to achieve superior rates of penetration to all othernozzle systems currently available in both laboratory and fieldtests. Three dimensional Computational Fluid Dynamics(CFD) models of the flow field between tricone bits andboreholes have been used to quantify the bit cleaning, bottomcleaning and cutting evacuation characteristics of this new bitand two other tricone nozzle designs.Cone cleaning is not the only factor to be considered indesigning a nozzle system for bit balling environments.Today’s rock bit is expected to drill long intervals andtherefore must drill through several different types of rock,which can often mean the bit may encounter several differentdrilling environments in its lifetime. Furthermore, nozzlesystems that clean the cones may erode the cones in abrasiveenvironments. CFD models have also been used to quantifyand minimize the potential for erosive wear of the cone shell.