Hydrate Modeling & Flow Loop Experiments for Water Continuous & Partially Dispersed Systems

A major industry concern is to reduce the severe safety risks associated with hydrate plug formation, and significantly extending subsea tieback distances by providing a cost effective flow assurance management/safety tool for mature fields. Developing fundamental understanding of the key mechanistic steps towards hydrate plug formation for different multiphase flow conditions is a key challenge to the flow assurance community. Such understanding can ultimately provide new insight and hydrate management guidelines to diminish the safety risks due to hydrate formation and accumulation in deepwater flowlines and facilities. The transportability of hydrates in pipelines is a function of the operating parameters, such as temperature, pressure, fluid mixture velocity, liquid loading, and fluid system characteristics. Specifically, the hydrate formation rate and plugging onset characteristics can be significantly different for water continuous, oil continuous, and partially dispersed systems. The latter is defined as a system containing oil/gas/water, where the water is present both as free water and partially dispersed in the oil phase (e.g., entrained water in the oil). This paper presents the results and analyses of flowloop experiments on partially dispersed systems as a function of water volume fraction and velocity/mixing. These experiments indicate that the partially dispersed systems tend to be problematic and are more severe cases with respect to flow assurance when compared to systems where the water is completely dispersed in oil. We have found that the partially dispersed systems are distinct, and are not an intermediate case between total water, and totally water-dispersed systems. Instead the experiments indicate that growth of hydrate sheet/deposit on the pipe wall because of the wetting of pipe walls by the free water layer coupled with bedding of the hydrates that are formed in bulk liquid seems to be the governing phenomena for hydrates growth in such systems. The data from the tests performed provide the basis for a mechanistic model for hydrate formation and plugging in partially dispersed systems. Lessons resulting from this work should be incorporated into flow assurance models, as well as operating company production strategies to reduce or mitigate hydrate plugging risks in complex multiphase systems.