A chemical based wet cold flow approach for addressing hydrate flow assurance problems
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Current gas hydrate flow assurance methods are becoming less economical and/or practical for deepwater operations, long tiebacks and ageing reservoirs. The industry thus needs novel flow assurance techniques to address these challenging conditions. An alternative approach called HYDRAFLOW, a chemical based wet Cold Flow method, has been presented in this thesis in which gas hydrate management, rather than prevention, is the aim. The idea is to convert most of the gas phase into hydrates and transfer it in the form of hydrate-slurry in the pipeline. This study investigates the concept, i.e. the transportability of hydrate slurries, for different systems (low and high GOR oil systems in the presence and absence of AAs) in different operating conditions, especially in conditions where the other flow assurance solutions either cannot be applied or are not economically viable, e.g. at high watercuts or under very high degree of subcoolings. The experiments involve investigating the rheological behaviour and flow properties of hydrate slurries using the HTI-set up (Helical Tube Impeller, an apparatus designed and build in-house for measuring viscosity of hydrate slurries at high pressures). Additionally, the rate of hydrate formation in low and high oil systems and also at subzero conditions has been measured. Furthermore, the effect of key variables, (e.g. heat transfer, mass transfer, degree of subcooling, salt, anti-agglomerants (AAs) and thermodynamic inhibitors) on the rate of hydrate formation and also on the rheology of hydrate suspensions have been studied in this work. The partitioning of a commercial AA between hydrate, oil and aqueous phases and its performances in each phase have also been determined which can help for decision making about recovering and/or recycling all or part of AAs. And finally, it has been shown that hydrate flow can potentially reducing wax deposition problems in pipeline by abrasion of the deposited wax.