It is becoming increasingly recognized that the flood of anthropogenic CO2 into the atmosphere should be reduced in order to mitigate the Earth’s atmospheric greenhouse and slow climate change. If immediate action is required, then a number of greenhouse gas reduction strategies may need to be implemented even before complete study of their impacts can be fully understood. Energy production through combustion produces large amounts of CO2 in a relatively small number of locations at which CO2 capture and compression to a liquid, transportable form can be achieved. Physical disposal offers the best option for sequestering this waste CO2. Because of the costs of transportation, geological sequestration will be most applicable for one set of power plants, deep ocean sequestration may be most applicable for some others. In both cases, the sequestration processes can provide some economic benefits. Ocean CO2 disposal can produce desalinated, treated water as a byproduct.

This article provides a comprehensive reference list to the extensive studies of marine natural gas hydrate surveys and studies on the northern Cascadian margin of Western Canada. The references are divided into each of the major study methods, surveys, analyses and conclusions. A number of MSc and PhD theses are included. We first refer to the articles that address the local tectonics and sedimentary accretionary prism in which the hydrate forms, then those that describe the numerous geophysical and geological surveys and studies, and finally the articles that address the most important conclusions that have resulted from this work on the distribution , concentrations, and amounts of hydrates, and on the processes of hydrate formation and dissociation.

Understanding when hydrates will nucleate has notable importance in the area of flow assurance. Attempts to model hydrate formation in subsea pipelines currently requires an arbitrary assignment of a nucleation subcooling. Previous studies showed that sII hydrate containing a model water-soluble former, tetrahydrofuran, would nucleate over a narrow temperature range of a few degrees with constant cooling. It is desirable to know if gas phase hydrate formers, which are typically more hydrophobic and hence have a very low solubility in water, also exhibit this nucleation behavior. In this study, differential scanning calorimetry has been applied to determine the hydrate nucleation point for gas phase hydrate formers. Constant cooling ramps and isothermal approaches were combined to explore the probability of hydrate nucleation. In the temperature ramping experiments, methane and xenon were used at various pressures and cooling rates. In both systems, hydrate nucleation occurred over a narrow temperature range (2-3°C). Using methane at lower pressures, ice nucleated before hydrate; whereas at higher pressures, hydrate formed first. A subcooling driving force of around 30°C was necessary for hydrate nucleation from both guest molecules. The cooling rates (0.5-3°C/min) did not show any statistically significant effect on the nucleation temperature for a given pressure. The isothermal method was used for a methane system with pure water and a water-in-West African crude emulsion. Two isotherms (-5 and -10°C) were used to determine nucleation time. In both systems, the time required for nucleation decreased with increased subcooling.

Here, we present a dissolution study of exposed hydrate from outcrops at Barkley Canyon. Previously, a field experiment on synthetic methane hydrate samples showed that mass transfer controlled dissolution in under-saturated seawater. However, seafloor hydrate outcrops have been shown to have significant longevity compared to expected dissolution rates based upon convective boundary layer diffusion calculations. To help resolve this apparent disconnect between the dissolution rates of synthetic and natural hydrate, an in situ dissolution experiment was performed on two distinct natural hydrate fabrics. A hydrate mound at Barkley Canyon was observed to contain a “yellow” hydrate fabric overlying a “white” hydrate fabric. The yellow hydrate fabric was associated with a light condensate phase and was hard to core. The white hydrate fabric was more porous and relatively easier to core. Cores from both fabrics were inserted to a mesh chamber within a few meters of the hydrate mound. Time-lapse photography monitored the dissolution of the hydrate cores over a two day period. The diameter shrinkage rate for the yellow hydrate was 45.5 nm/s corresponding to a retreat rate of 0.7 m/yr for an exposed surface. The white hydrate dissolved faster at 67.7 nm/s yielding a retreat rate of 1.1 m/yr. It is possible these hydrate mounds were exposed due to the fishing trawler incident in 2001. If these dissolution experiments give a correct simulation, then the exposed faces should have retreated ~ 3.5 m and 5.5 m, respectively, from 2001 to this expedition in August 2006. While the appearance of the hydrate mounds appeared quite similar to photographs taken in 2002, these dissolution experiments show natural hydrate dissolves rapidly in ambient seawater. The natural hydrate dissolution rate is on the same order as the synthetic dissolution experiment strongly implying another control for the dissolution rates of natural hydrate outcrops. Several factors could contribute to the apparent longevity of these exposed mounds from upward flux of methane-rich fluid to protective bacterial coatings.

The dissociation behavior of the CH4+CO2 binary gas hydrate has been investigated using Nuclear Magnetic Resonance (NMR) spectroscopy. This technique allows us to distinguish the hydrate structure present, as well as to quantify phase concentrations. Single-pulse excitation was used in combination with magic-angle spinning (MAS). Time-resolved in situ decomposition experiments were carried out at different compositions in sealed, pressurized samples. The decomposition profiles of the CH4+CO2 binary gas hydrate system obtained at various compositions suggest that the decomposition rate is a strong function of the fractional cage occupancy and temperature. An unexpected CH4 hydrate reformation was observed during our decomposition experiments when the temperature reached the ice melting point. A decrease on the CO2 content in the hydrate phase was found during the decomposition experiment, as the pressure and temperature of the system increases.

The oil and gas industry is often plagued by the formation of clathrate hydrates in oil pipelines. While the industry originally had a heuristic of avoidance of clathrate hydrates they are moving to a heuristic of risk management. To successfully implement a risk management heuristic, time dependent phenomena of clathrate hydrate formation and flowline plugging must be known. The study of time dependent phenomena of formation and agglomeration are investigated using a TA Instruments AR-G2 rheometer with a pressure cell capable of operating at up to 13.8 MPa. Pressurized rheological experiments examine clathrate hydrates formed in situ. Both shear and oscillatory experiments have been conducted on the samples, giving flow and viscoelastic parameters. Shear experiments show sharp increases in viscosity upon clathrate hydrate formation indicating rapid aggregation. Transient oscillation experiments show a sharp increase in the elastic and loss moduli followed by a decrease in the loss moduli. Thus, both in situ clathrate hydrate formation and annealing are quantified. In addition these oscillatory measurements provided a novel technique for non-destructive investigation of clathrate hydrate aggregation over time.

As the oil industry moves from a heuristic of avoidance of hydrates to a heuristic of risk management time dependent phenomena of hydrate formation and plugging must be known. One of the key parameters to this process is the aggregation of hydrate particles, the fractal networks they form, and the effect these two parameters have on flow. Unfortunately the aggregation and fractal structure information is extremely difficult to acquire experimentally, for this reason a three-dimension discrete element method (3D-DEM) model has been implemented. The 3D-DEM model calculates detailed solutions to Newton's equations of motion for individual particles. In addition these particles are coupled with the surrounding fluid through computational fluid dynamics (CFD). This coupled 3D-DEM can be used to investigate what the effects of shear, suspending viscosity, attractive forces, and other relevant variables have on the structure, stresses, and positions of the hydrate particles over time. In addition, the effect on viscosity has been calculated using CFD and compared back to basic hard sphere theory.

Hydrate plugging of hydrocarbon production conduits can cause large operational problems resulting in considerable economical losses. Modeling capabilities to predict hydrate plugging occurrences would help to improve facility design and operation in order to reduce the extent of such events. It would also contribute to a more effective and safer remediation process. This paper systematically describes different operational scenarios where hydrate plugging might occur and how a hydrate plug formation prediction tool would be beneficial. The current understanding of the mechanisms for hydrate formation, agglomeration and plugging of a pipeline are also presented. The results from this survey combined with the identified industrial needs are then used as a basis for the assessment of the capabilities of an existing hydrate plug formation model, called CSMHyK (The Colorado School of Mines Hydrate Kinetic Model). This has recently been implemented in the transient multiphase flow simulator OLGA as a separate module. Finally, examples using the current model in several operational scenarios are shown to illustrate some of its important capabilities. The results from these examples and the operational scenarios analysis are then used to discuss the future development needs of the CSMHyK model.

A number of notable studies on pure ionic clathrate hydrates have utilized their unique ionic characteristics for electric applications, including their use as an electrolyte for nickel-metal hydride batteries. Although quaternary ammonium salt hydrates have recently been applied to gas separation and storage areas with the expectation of the small co-guest occupancy in empty cages, most of the researches have been oriented to macroscopic approaches based on hydrate phase equilibria and many other process variables. On the other hand, spectroscopic analyses for identifying the structure transition of ionic clathrate hydrates together with a comprehensive consideration of their complex phase patterns have not yet been reported in spite of their importance to the energy and environmental fields. Accordingly, in this study, we present the report of an extraordinary structural transition accompanying the occurrence of more than two coexisting clathrate hydrate phases and channel-induced tuning pattern in ionic double hydrate systems. In particular, the tuning observation uniquely occurring in the ionic clathrate hydrates is quite surprising, even though the tuning behavior is more commonly observed in the non-ionic hydrate systems. The remarkable feature of this work is that the icy ionic hydrate materials can be effectively used in energy devices. Moreover, the microscopic analyses of ionic clathrate hydrates for identifying the physicochemical characteristics are expected to provide new insights into a variety of inclusion chemistry fields.

It is well known that methane hydrate undergoes several phase transformations at high pressures. At room temperature and low to moderate pressure, methane and water form a stable cubic structure I (sI) hydrate that is also known as MH-I. The structure is transformed to a hexagonal phase (sH/MH-II) above 1.0GPa. Another phase transformation occurs above 1.9GPa where the filled ice structure (MH-III) is stable up to 40 GPa before a new high pressure phase transition occurs. Experiments at such high pressures have to be performed in a diamond anvil cell (DAC). Our main interest, though, is to form sH methane hydrate at a lower pressure than reported in previous studies but with some methane in the large cages consequently increasing the methane content. This can be accomplished by introducing the molecules of the large hydrate forming substance (tert-butyl methyl ether/TBME) at a concentration slightly below the stoichiometric amount as suggested by molecular dynamics simulations. In this study we have synthesized mixed methane hydrate of sI and sH and loaded the clathrate with methane into several DACs. Raman spectra were collected at room temperature and pressures in the range of 0.1 to 11.3 GPa. The existence of sH methane hydrate was observed down to 0.2 GPa. However, the existence of methane in the large cages was visible only at pressure higher than 1.0 GPa. The excess methane in the system apparently destabilizes the sH clathrate at pressure below 1.0 GPa as it transforms to sI clathrate.