Characterizing water-in-oil emulsions with application to gas hydrate formation
Aichele, Clint Philip
Chapman, Walter G.
Doctor of Philosophy
This thesis implements nuclear magnetic resonance (NMR) techniques to directly measure water-in-oil emulsion properties and gas hydrate formation. This thesis introduces a novel application of the pulsed field gradient with diffusion editing (PFG-DE) NMR technique to measure drop size distributions of emulsions. The PFG-DE technique agrees with the standard pulsed field gradient (PFG) technique for a variety of emulsions. For the first time, this thesis utilizes the PFG-DE technique, coupled with the Carr-Purcell-Meiboom-Gill (CPMG) technique, to directly measure and quantify gas hydrate formation in emulsified systems. These unique data for black oil emulsions aid in developing effective flow assurance strategies. To elucidate emulsion formation mechanisms in well defined shear fields, this thesis implements Taylor-Couette flow to form water-in-oil emulsions. A range of oil viscosities is considered by selecting two crude oils that differ in viscosity, and each crude oil is matched with a model oil of similar viscosity. For the low viscosity crude/model oil systems, the computational fluid dynamics (CFD) simulations show that the intensity of Taylor vortices increases at higher rotational speeds, and this leads to multimodal drop size distributions. For the high viscosity crude/model oil systems, the CFD simulations show that the flow field is simple shear for all rotational speeds. The high viscosity crude oil emulsions exhibited multimodality for all rotational speeds investigated, while the corresponding model oil emulsions exhibited broad, smooth drop size distributions. In contrast to Taylor-Couette flow, this thesis also examined emulsification in complex flow conditions with inhomogeneous shear using a six bladed Rushton turbine. This work supplies transient drop size distributions for two crude oils. This work provides emulsion formation and stability characteristics for both high and low mixing speeds, as well as comparisons to established models that predict emulsion drop size in turbulent flow. Recent evidence suggests a relationship between water-in-oil emulsion morphology and gas hydrate blockage formation. An experimental setup to measure emulsion properties during gas hydrate formation was constructed, and the resulting NMR measurements indicate that for three of the four oils investigated, gas hydrate shells form around the water drops with thickness approximately equal to 1 mum.