Carrying Capacity of Drilling Muds

Abstract

Abstract The trend toward deeper drilling, together with the attendant increase inpower requirements for circulation of the drilling fluid, has emphasized theneed for a critical examination of the factors affecting the removal of bitcuttings from the hole by the drilling fluid. The ability of drilling fluids tolift cuttings is called their carrying capacity. A series of laboratory and field experiments has been conducted to determinethe minimum annular velocity necessary to remove cuttings, and to investigatethe effects of properties of drilling fluids on their carrying capacities. Consideration of the results of these experiments led to the followingconclusions:Turbulent flow in the well annulus is most desirable from the standpointof cutting removal.Low viscosity and low gel are advantageous in removing cuttings.Increase in mud weight is effective in increasing carrying capacity.The carrying capacity is higher when the pipe is rotated than when it isnot.If turbulent flow can be maintained, an annular velocity slightly higherthan the slip velocity of the largest cuttings to be transported should keepthe bore hole clean. This implies velocities of 100 to 125 ft per minute ratherthan the presently used 175 to 225 ft per minute. Introduction Power Savings by Reduction of Annular Velocities A large portion of the power expended in drilling operations is consumed incirculating the drilling fluid. An important factor in establishing the rate ofmud circulation is the minimum velocity in the annulus necessary to remove bitcuttings. Empirically, it has been found that average annular mud velocities ofabout 200'Ft per minute will remove cuttings. It was not definitely known, however, whether annular velocities of about 200'Ft per minute were just abovethe minimum necessary to remove cuttings, or whether such velocities could bematerially reduced without sacrifice of the ability of the mud to removecuttings. It is apparent that if annular velocities could be reduced withoutimpairment of cutting removal, a considerable saving in power requirementswould result. T.P. 3026