An Experimental Evaluation Of Correlations Used For Predicting Cutting Slip Velocity
Authors: Sample K.J. , Bourgoyne A.T. 
Published: December 2007

Abstract
Several particle slip velocity correlations have been developed for predicting the carrying capacity of drilling fluids. In this investigation, the published correlations of (1) Preston Moore, (2) published correlations of (1) Preston Moore, (2) Sze-Foo Chien, and (3) Walker and Mayes were evaluated using data obtained in the laboratory under both static and flowing fluid conditions. Data previously published by Sifferman et al. using a previously published by Sifferman et al. using a full-scale vertical annulus also was utilized in this investigation.
In addition, a new simplified approach was developed for establishing the carrying capacity of drilling fluids. The procedure involves the use of cutting slip-velocity measurements taken in a static column of fluid. This value for slip velocity is then used to predict cutting transport for flowing conditions. Cutting transport ratio provides an excellent measure of carrying capacity. A convenient linear relationship was found to exist between cutting transport ratio and the reciprocal of annular velocity.
When each of the proposed correlations and the new technique were evaluated with respect to the experimental data, the new technique was the only procedure to consistently yield results of acceptable procedure to consistently yield results of acceptable accuracy for the engineering design of drilling operations. Of the three published correlations evaluated, the method proposed by Preston Moore provided the best agreement with the experimental provided the best agreement with the experimental data.

Introduction
The primary function of drilling fluids in the rotary drilling process is to clean the rock fragments from beneath the bit and transport these cuttings to the surface. Drilling problems related to carrying capacity can result from insufficient as well as excessive annular velocities. When annular velocities are insufficient to effectively transport cuttings to the surface, problems of decreased bit life and slow penetration rates can occur. These problems result penetration rates can occur. These problems result when cuttings are reground several times before they are removed from the bit area. Cutting concentration buildup in the annulus can result in hole fill-up near bottom during trips and even stuck pipe if the cuttings pack off around the drill collars. Lost circulation problems can also occur if the increased cutting concentration produces a sufficient increase in mud density to cause formation fracture.
It also must be recognized that excessive annular velocities can cause a reduction in penetration rate. Frictional pressure losses penetration rate. Frictional pressure losses experienced in the drillstring increase as the drilling fluid velocity increases. When the frictional pressure losses in the drillstring are high, the fluid energy available for cleaning at the bit is greatly reduced, again resulting in wasteful regrinding of the rock fragments and poor bottom-hole cleaning. These factors indicate that an optimum annular velocity does exist that is related to the carrying capacity of the drilling fluid in use.
The purpose of this investigation is to evaluate experimentally the available slip-velocity correlations used for determining the carrying capacity of drilling fluids. The correlations included in this study are those of Preston Moore Sze-Foo Chien, and Walker and Mayes. In addition, a new technique for determining carrying capacity is presented and evaluated. Experimental data used in presented and evaluated. Experimental data used in the evaluation were obtained in Newtonian and non-Newtonian fluids for both static and flowing conditions. This investigation used data obtained in the laboratory as well as data previously published by Sifferman et al. using a full-scale published by Sifferman et al. using a full-scale vertical annulus.
PREVIOUS INVESTIGATIONS PREVIOUS INVESTIGATIONS Williams and Bruce were among the first researchers to recognize the need for establishing a minimum average annular velocity to remove formation cuttings from the borehole. In 1951, they published a classic paper on the carrying capacity of published a classic paper on the carrying capacity of drilling muds.