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Gas hydrate kinetics, transportability, interfacial phenomena and novel measurements applied to develop a new transient partially dispersed and segregated multiphase flow model for field applications
Brock, Christopher James
Brock, Christopher James
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2025
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2026-11-11
Abstract
Oil and gas flowlines operating at high pressure in subsea or cold terrestrial environments are at risk of forming crystalline gas hydrate (typically sII) deposits and plugs during transient scenarios, when warm reservoir fluids that would heat the flowline during steady-state operation are no longer flowing. The presence of a free water phase, being correlated with increased risk of gas hydrate plugging, also corresponds to being the least well understood gas hydrate/multiphase flow scenario, especially when transient flow phenomena are prevalent, and the flowline geometry includes inclines. Gas hydrate plugs are costly to remediate and can result in long operational downtimes, and they pose potential environmental and safety concerns. Commonly used hydrate remediation field techniques, such as one-sided depressurization, pose safety concerns, as the pressure differential across a plug can cause detachment from the pipe wall, forcing the plug to travel as a high velocity projectile, potentially impacting inline equipment, and causing damage or injury to equipment and personnel. Predicting the formation of gas hydrate deposits and plugs based on principles, including interfacial science and multiphase flow engineering, is a critical yet outstanding need, and understanding the mechanical properties of the resulting gas hydrate plugs can aide in their successful remediation.
This thesis work has developed a new conceptual picture for gas hydrate formation and plugging phenomena in partially dispersed and segregated multiphase flow, and a mechanistic model to assess gas hydrate formation kinetics, bedding/deposition, deposit sloughing, and plugging risk in partially dispersed and segregated systems. This work also developed and applied a multiscale laboratory approach to study and validate the new transient hydrate model and the mechanistic phenomena it incorporates, including deposition, sloughing, and interfacial behavior of the hydrate/solid interface. Gas hydrate deposition and sloughing behavior, which are poorly understood and rarely quantified, were studied in a model condensate/water/gas partially dispersed system via the use of a high-pressure once-through deposition flowloop, where the critical shear stress required to slough gas hydrate deposits was quantified, which is used to inform the transient gas hydrate model. Solid THF model hydrate and mixed CO2/THF sII hydrate plugs were studied (via both mechanical and novel hydraulic plug displacement techniques) to understand the impact of subcooling, surface roughness, surface wettability, and applied stress rate on the yield strength and failure mechanisms of gas hydrate plugs.
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