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

Abstract

ABSTRACT Conventional roller cone bit hydraulics optimization techniques focus on minimizing circulation losses to deliver maximum power or impact force to the bit. Little emphasis has been placed on optimizing the bottom hole cleaning process by itself, even though it is highly influential in both penetration rate and bit life. Optimization of bit and bottom hole cleaning requires the elimination or minimization of flow stagnation in the open spaces between the rolling cones and the enhancement of shear flow and turbulent pressures across the hole bottom. Better understanding of this flow opens the door for improved bit design and better allocation of hydraulic energy to improve the efficiency with which the bit and hole bottom surfaces are kept free of cuttings and fines. This paper presents the results of a numerical study of the highly turbulent, three-dimensional flow surrounding an 8 1/2″ IADC 517 class roller cone rock bit. The computations were performed using a three-dimensional finite element computer code (N3S). Numerical predictions were verified by full-scale laboratory experiments consisting of wet paint flow visualization tests on the exposed surfaces of the bit, high-speed photography of plastic particles to determine flow velocities and measurements of the mean and fluctuating pressures on the borehole bottom. A similar approach has been used successfully to improve nozzle arrangements and bit geometry on easier-to-model PDC bits. This paper verifies that the same methodology is applicable to the more complex and highly disturbed flows around a roller cone rock bit and may bring about comparable improvements.