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Interfacial and kinetic studies of some clathrate hydrates
Ismail, Nur Aminatulmimi
Ismail, Nur Aminatulmimi
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2022
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2024-04-22
Abstract
Clathrate hydrates, also generally known as hydrates, are ice-like crystalline compounds, in which light hydrocarbon molecules are encaged in a host lattice composed of hydrogen-bonded water molecules. Hydrates have received considerable attention for their important role in oil and gas production and transportation due to the formation of hydrate blockages, and for their application in sustainable technologies. With the oil and gas industry innovations towards exploration in more extreme environments, hydrates become more prevalent. At the same time, many research efforts have been conducted to exploit a variety of hydrate-based technologies (e.g., energy recovery/storage). For the advanced hydrate management strategy in the flowlines, as well as the application of hydrate technologies, it is essential to understand the interfacial properties and kinetics of hydrates. Hydrate management strategies to prevent hydrate blockages from occurring include the injection of hydrate inhibitor chemicals. One of the attractive alternatives to synthetic hydrate inhibitors is exploitation of a non-plugging oil (with surface active molecules acting as natural anti-agglomerants, AAs). Hence, it is important to evaluate an oil for its potential as a non-plugging oil, considering its significant economic savings, since the properties to prevent hydrate plugging already exist in the oil without additional cost. This work provides new understanding of hydrate behavior related to flow assurance by focusing on gas hydrate interparticle interactions in the presence of non-plugging oils, and the interactions between gas hydrates and water droplets in a liquid hydrocarbon phase. Knowledge of the latter hydrate-droplet interactions is severely limited, especially in the presence of non-plugging oil. A new experimental method using the High-Pressure Micromechanical Force (HP-MMF) apparatus was developed that enabled representative oil sampling. Using this method, the non-plugging potential of seven oil samples were evaluated from the gas hydrate interparticle cohesive force. Significant reduction of up to 99.8% to the cohesive force demonstrated by specific oils was attributed to the presence of natural surfactants that play the role as AAs. Based on the reductions, these oils can be categorized as potential non-plugging oils with lower risk of hydrate particle agglomeration. The gas hydrate interparticle cohesive forces measured in this thesis work will be used as the input to the hydrate agglomeration model that is incorporated in the in-house multiphase flow software (i.e., CSMHyK coupled to OLGA). Using directly measured cohesive forces from the thesis results will help to increase the accuracy in the computational simulations. In addition, the HP-MMF method was found to be a unique tool that can be utilized for the detection of asphaltene-hydrate mixed agglomerates. The results from the work also elucidated new knowledge/quantification for the hydrate-droplet interactions that are more significant than the interparticle interactions. For an advanced hydrate management strategy in flow assurance as well as the application of a gas hydrate technology, it is important to understand the kinetics and morphologies of gas hydrate crystals during the growth period in saline water. In this work, a novel seed/template crystal method was established to investigate the effect of salinity to the sII tetrahydrofuran (THF) hydrate growth kinetics rate and morphology. For the experiment performed in the presence of 3.5 wt.% NaCl, the single crystal growth rates were retarded by an average of ~83% that can be attributed to the salt exclusion at the growing crystal interface. Considering the increased interest in the application of gas hydrates, microscale studies were conducted to gain insight into the kinetics for mixed CO2/C2H6 hydrate using confocal Raman spectroscopy. In all the Raman measurements, peaks representing both CO2 and C2H6 were detected on the selected hydrate crystals, indicating no inhibition effects from either CO2 or C2H6 for incorporation of the guests into the cavities of a sI hydrate structure. Analysis using Raman mapping showed that the surface of hydrate crystals was heterogeneously distributed, with the composition varied across the crystal surface area.
With the ability to store and concentrate gases inside the hydrate lattice, the exchange kinetics process of pure CH4 in gas hydrate cages by CO2 was investigated. Capture/storage of CO2 in a hydrate lattice presents an attractive potential solution for sustainable technologies. In this work, the exchange kinetics process of pure CH4 in gas hydrate cages by CO2 was studied microscopically and by using in-situ laser Raman spectroscopy. The transformation of the CH4 hydrate crystals to mixed CH4-CO2 hydrate was investigated for their exchange/dissociation kinetics for CH4 hydrate into mixed CH4-CO2 hydrate at different penetration depths. It was found from this work that the incorporation of CO2 into the hydrate phase follows a concentration gradient from the surface to the core of the hydrate particle, supporting the shrinking core model.
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