Phase Field Approaches to the Kinetic Modeling of Hydrate Phase Transitions
Bjørn Kvamme, Atle Svandal, Trygve Buanes, Tatyana Kuznetsova, 2009. "Phase Field Approaches to the Kinetic Modeling of Hydrate Phase Transitions", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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A phase field theory (PFT) with model parameters evaluated from atomistic simulations and experiments is applied for describing the nucleation and growth and the dissolution of CO2 hydrate in aqueous solutions under conditions typical to underwater natural-gas-hydrate reservoirs. We show that the size of the critical fluctuations (nuclei) is comparable to the interface thickness, and thus the PFT predicts a considerably lower nucleation barrier height and higher nucleation rate than the classical approach that relies on a sharp interface. The growth rates of CO2 hydrate corresponding to different growth geometries (planar, circular, and dendritic) have been determined. The predicted growth rates are consistent with experiments performed under similar conditions. An alternative phase approach, based on cellular automata, has also been formulated and applied to the same model systems. Time dependence for this approach is derived by relating the diffusivity to the interface thickness. For small times, the two approaches appear to give similar results but deviate significantly for larger time scales. Dissolution rates of the hydrate phase have been studied as a function of CO2 concentration in the aqueous solution. On the basis of a simple model of foreign particles, qualitative simulations were performed to describe hydrate formation in porous media. The Avrami-Kolmogorov exponent evaluated from these simulations varies substantially with the volume fraction occupied by the foreign particles.
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In September 2004, the American Association of Petroleum Geologists (AAPG) convened a Hedberg Research Conference in Vancouver, British Columbia, Canada titled "Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards." As a continuation of the Hedberg Research Conference in Vancouver, the conveners of the conference and the editors of this Memoir have worked with more than 150 authors and coauthors to prepare this Memoir on gas hydrates. This publication follows the goals of the Hedberg conference; however, the contents of this Memoir were expanded to include all aspects of gas hydrates in nature. This Memoir contains 39 individual contributions, ranging from long topical summaries to shorter focused research papers. This Memoir has been published in two parts, with digital versions of all the complete research papers included on the enclosed CD. The hardcopy portion of the Memoir includes abstracts and several key figures for each of the contributions along with a complete copy of a gas hydrate technical review. The digital portion of this Memoir has been organized into a series of topical sections consisting of review articles, marine gas hydrate papers, and gas hydrate laboratory and modeling studies. Because of the rapidly emerging worldwide interest in gas hydrates, this comprehensive treatise on the geology of gas hydrates will be valuable to both the gas hydrate research community and exploration/development geologists working in arctic and deep marine environments.