Hydrate Prevention by Anti-Agglomerants - Parameters Impacting Flow Performance in Systems Where Hydrates are Present
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Natural gas hydrates are crystalline compounds that, under the right pressure and temperature conditions, may form in hydrocarbon pipelines, causing transport complications. Several methods of countering this have been used in the industry, one of them being the injection of anti-agglomerants. Anti-agglomerants do not prevent hydrates from forming, but prevent plugging by effectively dispersing the hydrate particles so that they can flow as a hydrate slurry. Even if the injected anti-agglomerants should prevent agglomeration and plugging of a pipe, deliverability issues might occur. For a system with high enough viscosity, the pressure drop along a pipeline could be high enough to regard the transportation as unfeasible. In this thesis, the viscosity of a system with a flowing hydrate slurry will be investigated based on specific process parameters. The selected parameters are chosen based on fundamental theory on the flow of suspensions. Their values are chosen to emulate a realistic scenario as accurately as possible. Parameters include the hydrate volume fraction, the particle size distribution, hydrate particle size and water cut. The different parameters are evaluated using a Matlab simulator provided by SINTEF. The model is developed by SINTEF as an aid for developing subsea oil and condensate fields by the CONWHYP (Conversion of water to hydrate particles) loop concept. Some modifications have been made to the model to simulate the desired system, as well as to how the model presents data. Simulation results show how all evaluated parameters influence the viscosity or pressure profile of the system. The slurry viscosity seems to be most sensitive to changes to the hydrate volume fraction, with high volume fractions yielding a higher viscosity. Variations to the particle size distribution are also significant, with sensitivity strongly dependent on the hydrate volume fraction. The results show that the viscosity increases with increasing monodispersity. For a uniform sample, the particle size does not influence the slurry viscosity, but will influence the pressure drop due to the change to the slurry friction factor. Results from water cut simulations show that a hydrate slurry system is highly sensitive to changes in the water cut, and corroborates the scientific literature, which states that anti-agglomerants do not perform well at higher water volume fractions.