Abstract
Experiments were carried out in a unique full-scale flow loop which includes a 73-ft (22.25 m) long annular section of 6-inch (152 mm) casing and 3.5-inch (89 mm) concentric drillpipe at elevated pressures and elevated temperatures (EPET) ranging from 185 to 500 psi (1.28 to 3.45 MPa), and 80 to 175 °F (26.8 to 79.44 °C) respectively. The gas-liquid ratio of the aerated fluids varied from 0.0 to 0.38. The in-situ cuttings concentration (i.e. volumetric concentration) was determined by using a special designed multiphase measurement system consisting of an air expansion tank, quick-closing valves, cuttings weighing system and two nuclear densitometers. The following test parameters were recorded during the experiments: liquid and gas flow rates, cuttings weight in the annulus, liquid holdup, mixture density and pressure losses.
The results clearly show that in addition to liquid flow rate and gas-liquid ratio (i.e. injection gas volume fraction calculated at test temperature and pressure), temperature essentially affects the cuttings transport efficiency and the associated frictional pressure drop. The volume of cuttings which accumulated in the annulus was very sensitive to the liquid flow rate. Elevated temperature was found to cause a significant increase in the cuttings concentration at given flow conditions. The injection of gas has a positive effect on the cuttings transport at high liquid flow rates (greater than 150 gal/min). However, it was found that at lower liquid flow rates (less than 150 gal/min), increasing gas-liquid ratio (GLR) results in a decrease in cuttings transport efficiency.
A mechanistic model for cuttings transport with aerated fluids under EPET conditions has been developed to predict frictional pressure loss and cuttings concentration in the annulus. The model is based on mass and momentum conservation equations and wall equations. Comparisons between the predictions of the model and experimental results show satisfactory agreement.
In summary, this paper presents several important new aspects of cuttings transport that will be very useful for practical underbalanced drilling (UBD) design.
