The Cutting Carrying Capacity of Air at Pressures Above Atmospheric

Abstract

Published in Petroleum Transactions, AIME, Volume 213, 1958, pages 180–185. Abstract The turbulent flow drag coefficients, or friction factors, have been experimentally determined for the cuttings normally encountered in drilling operations. The gas law and average drag coefficients for characteristically flat particles (limestones and shales) and for angular to sub-rounded particles (sandstones) were used to extend Newton's equation to a more useful form. The resulting equations are expressions for the slip velocity of a particle as a function of the particle size and shape, the bottom-hole injection pressure, and the bottom-hole temperature. The velocities necessary to lift actual rock cuttings as observed in the laboratory were compared with velocities predicted from the derived equations. Results indicate that there is no single correct circulating velocity and that the commonly used 3,000 ft/min linear velocity may be sufficient to lift only very small particles. Introduction A promising departure from rotary hydraulic drilling is air or gas drilling. In many instances the rate of penetration and bit life increases resulting from this method have been very substantial. Further the application of air drilling in areas of lost circulation or water sensitive pay zones has been highly successful. Purpose For the drilling contractor, the practical question remains, "How much air pressure and volume should I have?" It is necessary to have a reasonable knowledge of the air velocities and pressures required in air drilling operations for the proper design and most advantageous use of surface equipment and for adequate removal of cuttings from the borehole. Based on experience, most operators agree that at least 3,000 ft/min linear velocity is necessary for satisfactory hole cleaning. It was the purpose of this investigation to evaluate the drag coefficients, or friction factors, for the cuttings normally encountered in drilling operations, i.e., sandstones, limestones and shales, and to utilize the values obtained to develop an expression for the minimum velocities and pressures (hence the volumes) necessary to lift these cuttings.