A Methodology Using Laboratory Experiments and Numerical Modeling To Optimize Roller Cone Bits Hydraulics

Abstract

Conventionalroller cone bit hydraulicsoptimization techniques focuson minimizing circulation lossesto deliver maximum poweror impact forceto the bit. Little emphasis has been placedon opdmizing the bottomhole cleaning processby itself, eventhough it is highly influential in both penetration rate and bit life. Optimization of bit and bottomhole cleaning requires the elimination or minimization of flow stagnation in the open spacesbetweentheroUingcones sndtheenhancement of shear flowand turbulent preamres across theholebottom. Better mkstadng of this flow opens the door for improvedbit design and better allocation of hydraulic energyto improvethe eiliciencywith which the bit and hole bottom surkes are kept free of cuttings and fines. This paper presents the results of a numerical study of the highly twbulen$ threedimensionsl flow surroundingan 8 1/2" IADC 517 class roller cone rock bit. The computationswere performedusing a threedimensiona.1finite elementcomputer code(N3S). Numericalpredictionswereverifiedby fidkscale laboratoryexperimentsconsisting of Wetpaint flow visualizationtests on the exposedaurkes of the bit high-speed photogmphyof plastic particles to determine flowVelocitiesand measmments of the mean and fluctuating presmres on the boreholebottom.A similar approach has been used successtMlyto improve References and illustrations at end of paper 237 A nozzle arrangementsand bit geometryon easier-to-modelPDC bits. This paper verifies that the same methodologyis applicable to the more complexand highly disturbed flowsaround a roller cone rock bit and may bring about comparableimprovements.