Browsing by Author "Okechukwu Aguguo, Johnbosco"

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    Numerical Simulation of Hydrate Dissociation in Pipelines via Single-sided Depressurization Approach and via Electrical Heating
    (2024-07-17) Okechukwu Aguguo, Johnbosco; Clarke, M. A.; Gates, Ian Donald; Azaiez, Jalal
    Hydrate plugging in petroleum pipelines poses serious flow assurance issues within the oil and gas community. Since its discovery by Hammerschmidt in 1934, researchers have undertaken several thermodynamic studies. Current techniques for dissociating hydrate plug during total blockage such as depressurization pose challenges in deep-water pipelines due to limited accessibility. This work builds upon previous models by employing a rigorous 2D model formulation that combines heat transfer and flows in porous media as a coupled process and using advanced CFD software (COMSOL Multiphysics software). The experimental data from both hydrate dissociation via electrical heating and single-sided depressurization were validated, and the simulation and experimental data exhibit a reasonable level of agreement for both hydrate dissociation via electrical heating and single-sided depressurization in both structures. However, minor discrepancies are observed, which may be attributed to potential digitization inaccuracies during data collection. A unique feature of this work is its ability to predict the interface's shape between hydrate and gas during hydrate dissociation. This study introduces a novel approach for modelling hydrate dissociation via single-sided depressurization by using dimensionless analysis the simulation data was summarized in a way that may allow researchers and industry people to perform an initial screening of a proposed plug depressurization scheme, without needing to resort to CFD simulations. Furthermore, incorporating the decomposition kinetics for hydrates formed for pure and mixed gases as a boundary condition in the 2D heat equation. It was found that hydrate dissociation kinetics has minimal to no effect on plug detachment time, suggesting that pipeline plug dissociation is primarily heat transfer limited. The investigation on sensitivity analysis reveals that hydrate plug detachment time depends significantly on numerous factors including hydrate structure, pressure ratio, and length to diameter ratio and pressure rate. Three different depressurization methods were used in this study, the results show that for Structure I-Hydrate, all three cases performed better by falling within the set safety limit. For Structure II-Hydrate, the multi-step depressurization approach was the best with minimum risk, followed by the ramp change method, while single-step was the least. In the simulation for a land-based case, results showed that in simulating hydrate plug decomposition in a pipeline for a land-based case with sinusoidal wall temperature, for a varying outer wall temperature, hydrate dissociates faster than what was observed with a constant wall temperature for all three depressurization strategies.