Effect of Pipe Eccentricity on Hole Cleaning and Wellbore Hydraulics
The consideration of pipe eccentricity and its impact on hole cleaning has not been widely reported in literature. Pipe eccentricity affects the average velocity of the drilling fluid in the annulus which is one of the most important factors considered in hole cleaning. In this study, developed equations of motion for a couette flow of non-Newtonian power-law fluid through an eccentric annulus are used to determine the effect of pipe eccentricity on hole cleaning. A graph for the velocity profile in the annulus is developed and the average velocity of the drilling fluid for each eccentricity factor is used to analyse the parameters that indicate hole cleaning efficiency. Some of the parameters include transport velocity, carrying capacity index, cuttings concentration, and equivalent circulating density. From the analysis, hole cleaning is said to be less effective when deviating from concentric annulus to highly eccentric annulus. Secondly high eccentricity can cause high losses of the drilling fluid after fracturing of the formation especially when the difference between the fracture pressure and the pressure of the formation is very small.