Research on Flow Field Characteristics Measurement in Variable Cross-Section Annulus Using Particle Image Velocimetry (PIV)

Abstract

Abstract The actual downhole annulus is irregular, a variable cross-section geometry, due to the difference between the diameter of tool joints, tubing collars or downhole tools and the inner pipes. With the increasing of well depth, it is difficult to predict the annulus pressure loss accurately due to the effect of variable cross-section geometry. Research on flow field characteristics in variable cross-section annulus is the theoretical foundation of accurate prediction on annulus pressure loss. However, there is still few research on flow field characteristics in variable cross-section annulus by experiment, especially by using PIV technology. PIV has become an efficient method for complex flow field visualization and analyzation. The results show that there is separated reattachment flow in the irregular annulus which mainly occurred in the downstream of the expansion. The separated reattachment flow has low velocity, but vortex mainly occurred in this area. The disturbance range of streamlines caused by expansion structure is shorter in the upstream than in the downstream. The first and second modes contain 82% energy contribution in the irregular annular flow field. And the first mode can effectively restore the large-scale structure. With the mode increases, it is found that the small-scale structure is mainly distributed in the shear layer of the separated and reattached flow downstream of the variable cross- section geometry.