An Experimental Study of the Annulus Pressure Drop in a Simulated Air-Drilling Operation

Abstract

Summary A comprehensive experimental wellbore model was built to simulate the multiphase flow of compressed air and sand that occurs in an air-drilling process. The model was designed to control the air volumetric flow rate and sand mass flow rate through a transparent annulus. The model also permitted observation of the sand and air in the annulus and allowed measurement of the pressure drop across the annulus. An empirical equation was developed for the minimum annulus pressure drop as a function of the sand mass flow rate through the system, the optimum annulus air velocity, the weight fraction of coarse sand particles entering the annulus, the weight fraction of coarse sand particles in the annulus, and solids loading in the annulus. The experimental results were compared with annulus pressures predicted by a semiempirical model of the air-drilling process developed by Angel. Angel's model failed to predict the observed minimum annulus pressure drops. In addition, the experimental results indicated that an annulus air velocity lower than the value assumed by Angel's model may be required.