Ability of Drilling Mud To Lift Bit Cuttings

Removal of bit cuttings is an important function of drilling muds. In aneffort to obtain better understanding of the factors influencing the removal ofcuttings, an extensive series of laboratory tests were made in which slipvelocities of various sizes and shapes of particles were measured in muds ofdifferent physical properties. Empirical equations were then derived from theseexperimental data. These equations show that slip velocity is dependent oncutting size and shape, mud flow constants, and flow state of the mud.Applicability of these equations for field use is demonstrated by comparingcomputed slip velocities with slip velocities obtained from field tests. Introduction Drilling muds have many functions, but perhaps the most important is theremoval of bit cuttings from the well. In a 10,000'Ft well, the weight of rockwhich is drilled and must be carried to the surface is over 150 tons. Inaddition to this, the mud must remove any sloughings from the well bore.Failure of the mud to promptly remove either bit cuttings or sloughs from thewell bore causes re-drilling and excessive wear on bit teeth, slows downdrilling rate thereby increasing well costs, and greatly increasespossibilities for stuck drill pipe when circulation is stopped for any lengthof time. Drilling muds lift bit cuttings to the surface by means of the upwardvelocity of the drilling mud in the annulus. Because a density differenceexists between the rock being drilled and the drilling mud, there is adifference between mud velocity and the rate of bit cutting travel, called thenet rise velocity. T.P. 2782