Fluid dynamics of well-bore bottom-hole cleaning /

Abstract

A comprehensive series of tests were run on the University of Oklahoma drilling research laboratory rig investigating the variables which influence the rate of cutting removal. No rock cutting or penetration was done in these tests as the bit was held at a preselected height, above a packed column of cutting. The parameters which were allowed to vary in the test included nozzle diameter, chip size, cutting density, mud density, mud plastic viscosity, yield point, mud flow rate, drill pipe RPM, bottom-hole pressure, pressure drop through the nozzles, nozzle distance from bottom of hole, hydraulic diameter of annulus and bore hole inclination angle. A regression analysis of the data indicated how the rate of cutting removal was a function of the above variable expressed in terms of dimensionless parameters such as Reynolds number, Froude number, rotational Reynolds number, etc. A study was also conducted on the effect of twelve different nozzle configurations on the rate of cutting removal.

The use of the curves and regression equations developed in this study should allow an engineer the opportunity to more closely optimize bottom-hole cleaning and, therefore, improve the rate of penetration and minimize drilling cost per foot.