A Comparative Study of Laminar-Turbulent Displacement in Eccentric Annulus Under Imposed Flow Rate Conditions

In this paper, we present and discuss an experimental study of fluid-fluid displacement in a fully eccentric horizontal annulus. Experiments were designed to simulate turbulent displacing flows, and the results are used to investigate the displacement processes in terms of interface dynamics and displacement efficiency. It is widely believed that turbulent flows are more efficient at displacement, but it is not always clear under what conditions this comparison is made. A set of experiments was conducted to investigate the role of flow regime under a constant imposed flow rate in the absence of any stabilizing buoyancy effect (i.e. iso-density fluids). Carbopol solutions are displaced with various concentrations of Xanthan gum, to simulate a drilling mud displaced by a spacer fluid. The flow regime of the displacing fluid spans from laminar to fully turbulent flow regimes. The displacement tests are all unsteady in a sense that wide-gap velocity is always faster than that of the narrow-gap. The displacement flows and interface dynamics are captured using optical techniques, and the images are post-processed to ascertain the displacement efficiency, interface velocity and elongation. We conclude with a discussion on the significance of outcomes achieved in this study, and also limitations of the experimental technique.