PRESSURE GRADIENT PREDICTION FOR DIFFERENT FLOW PATTERNS OF HEAVY OIL AND NATURAL GAS IN A HORIZONTAL PIPE USING CFD TECHNIQUES AND EMPIRICAL CORRELATIONS

Abstract

Two-phase flows are of fundamental importance in the petroleum industry, considering that most petroleum reservoirs produce oil and gas simultaneously. Because system pressure gradient is a result of the frictional effects between fluids and pipe wall, and the interfacial effects between the fluids themselves, the precise determination of this parameter is complex. Many authors have sought to predict pressure gradient by using computational fluid dynamic techniques and empirical correlations. The present work aims to compare heavy oil and natural gas mixture pressure gradients in a horizontal pipe for different flow patterns using the application ANSYS CFX 13.0, Lockhart and Martinelli, and Beggs and Brill correlations. The analysis investigated the results for bubbly, plug, and stratified flows. The results showed that Beggs and Brill over predicted pressure gradient values. It was also observed a good agreement between numerical and Lockhart and Martinelli correlation for bubbly and plug flows, with root-mean-square deviations (RMSD) of 5.78 and 19.55 percent, respectively. As for the stratified flow cases, the numerical results presented a poor agreement, with a RMSD greater than 90 percent. The high percent deviation for this flow regime is due to the increase in the gas input content. To compute the high gas velocity effects and, hence, improve the agreement, we suggest the use of turbulence and free surface models as well as different values of drag coefficient in the numerical setup.