| Summary: | This thesis describes experimental and numerical simulation work that has been carried out on the naturally occurring polymer guar gum and the commercial wormlike micelle solution ClearFRAC. Both of these fluids are used in the hydraulic fracturing process, which improves the rate of oil recovery. The rheology has been studied at different temperatures and in the case of guar gum at different concentrations, in both controlled strain and controlled stress parallel plate rheometers. The features observed in each fluid are typical for the class of fluids to which they belong. The effect of particulate and air inclusions on the rheology was studied, as was the formation of filaments of the fluids. Optical microscopy under shear flow revealed the formation of chains of tracer particles or air bubbles under certain conditions in both fluids. The wormlike micelle solution exhibited intermittent slip and the separation of the flow into regions of different flow rates. The application of shear induced a change in the transparency of the wormlike micelle solution when viewed in visible light and this is believed to be the first direct light observation of shear enhanced concentration fluctuations in a wormlike micelle solution. The fluids have been examined systematically in progressively more complicated geometries using pressure drop measurements, transmitted light, reflected light, scattered light and flow birefringence. Finite element modelling has been performed using the commercial package Polyflow to examine the effect of viscosity, elasticity, plasticity and inertia on the different flow geometries. The Cross model provided the best description of the behaviour of the guar gum solutions, whilst the wormlike micelle solution was well modelled by both the Cross and Herschel Bulkley models. The Wagner equation revealed the effects of elasticity on the flow.
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