Improved Drilling Performance With Enhanced Crossflow Rock Bits

Abstract

After review of the literature on drilling hydraulics and evaluation of two-nozzle drilling, specially designed two-nozzle enhanced crossflow rock bits were manufactured and tested. Performance analysis indicates a 12 to 16% increase in drilling rate over standard three-nozzle jet bits. Laboratory and preliminary field test results are presented. Introduction Many drilling people are not aware of the number of successful and unsuccessful field tests conducted in the last 15 years on special bits designed to improve bottomhole cleaning. Many of the successful test bits were not reported or offered for standard field usage because drilling cost reductions were negated by increased bit development and manufacturing costs. Today, drilling costs have risen to a level where a slight increase in drilling rate performance will result in sizable cost savings.One basic hydraulic improvement was made when jet nozzles were incorporated into bit design in the late 1940's. Surface equipment requirements changed, and a period of drilling hydraulics study commenced. Most drilling people are aware of several studies and articles published on the subjects of bottomhole cleaning, chip-removal forces, crossflow, extended-nozzle bits, and two-nozzle bits. Review of the Literature A basic relationship of nozzle flow and crossflow on an impingement plate was deduced by Poreh and Cermak. The resulting crossflow, Vc, was directly proportional to the square root of the product of flow volume through a nozzle and the nozzle velocity.McLean, in studies conducted in 1964 and 1965, concluded that maximizing crossflow should produce the maximum use of available bit hydraulic horsepower. These studies included laboratory tests which measured crossflow distribution resulting from jet impingement on an actual rock bit. McLean determined the relative crossflow velocity at various points on the hole bottom due to jet impingement. The velocity parallel to the hole bottom at various locations was (1) where Vc = crossflow velocity, ft/s (m/s), k = geometric constant, Q = nozzle flowrate, gal/min (dm3/min), V = nozzle velocity, ft/s (m/s), and D = bit size, in. (cm). For the normal range of flow rates used in rotary drilling, the maximum crossflow will occur at the maximum bit hydraulic horsepower condition.In 1971, Sutko and Myers concluded that hole cleaning and drilling rate should improve as the number of nozzles is decreased. Hole cleaning and drilling rate should improve as nozzle standoff decreases. JPT P. 1687＾