LAUSR

An experimental study was conducted to investigate how the fluid elastic properties would influence, the frictional pressure drops, the critical velocity for the onset of the bed erosion, and turbulent flow characteristics (i.e. Reynolds stress, axial and radial turbulence intensity profiles) of the polymer fluid flow over the stationary sand bed deposited in horizontal pipeline. A 9m long horizontal flow loop (pipe ID: 95 mm) equipped with particle image velocimetry (PIV) system was used for the experiments. The polymer fluids, which had almost identical shear viscosity characteristics while showing significantly different elastic properties (quantified in terms of relaxation time) were used together with 30/50 mesh size industrial sands in the bed erosion experiments. Polymer fluids were prepared by mixing three different grades (i.e. 5×105, 8×106, 20×106 g/gmol) of partially hydrolysed polyacrylamide (HPAM) polymer. After determining the critical velocities for the onset of the bed erosion using both fluids, the frictional pressure drops at critical and several subcritical velocities were recorded for both fluids. Additionally, instantaneous near bed velocities were measured by using the PIV technique. Further analyses of the velocity data obtained by PIV technique, we were able to determine the turbulent flow features such as Reynolds stress, axial and radial turbulence intensity profiles. Results showed that the fluid elasticity affects the bed erosion dynamics significantly. Generally, frictional pressure drops, and critical velocities for the bed erosion all increased with the increasing fluid elasticity. This paper presents results of an experimental study where the PIV technique was used to investigate the bed erosion dynamics due to the turbulent flow of elastic polymer fluid over the stationary sand beds. Fluids were prepared using a special technique, which allowed us to alter the fluid elastic properties while keeping the shear viscosity constant. By conducting experiments under controlled conditions, for the first time in drilling literature, we were able to quantify the individual effect of the fluid elasticity (independent from shear viscosity) on the critical flow rate for bed erosion and the turbulent flow characteristics of polymer fluid flow over the stationary sand bed.