Buoyancy driven slump flows of non-Newtonian fluids in pipes

We present results of a comparative experimental-numerical study of the buoyancy-driven slumping flow of two non-Newtonian fluids in a horizontal closed pipe. This type of flow occurs during the abandonment of horizontal oil and gas wells, when sealing the well through the setting of cement plugs. In our study, both of the fluids exhibit shear-thinning behaviour and one of the fluids has a yield stress. The yield stress is necessary in order for the flow to have a static equilibrium. We have studied the effects of changes in density difference and of small deviations from perfectly horizontal. The effects of these parameters on the interface shape and on the slump length versus time were analyzed. Comparison of numerical and experimental results shows broadly similar trends, but with some qualitative differences also observed, possibly due to interfacial effects at the interface. We also compare the slump length and shape against existing analytical results that predict the maximal static slump length.