Browsing by Subject "Methane hydrate"
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Item Characterizing the petrophysical properties of shallow marine environments and their potential as methane hydrate reservoirs(2015-05) Nole, Michael Anthony; Daigle, Hugh; Mohanty, KishoreIn shallow marine sedimentary environments, characterization of sediment petrophysical and thermodynamic properties is imperative for understanding the subsurface transport of fluids and their chemical constituents. This work first presents an objective method of scanning electron microscope image analysis that directly quantifies microporosity in clay-rich, fine-grained sediments typical of the shallow marine subsurface. The method is powerful because it is fast, easy, and provides a direct microporosity estimation technique to augment or replace experimental data. When used appropriately, the method can be implemented on microporous sediments and sedimentary rock in general. With an understanding of how microporosity manifests in shallow marine sediments, the impact of small pore sizes on methane hydrate solubility is then examined for core samples taken from 3 sites in the Nankai Trough offshore Japan, an area that has been heavily surveyed in recent years for its potential to host economically recoverable deposits of methane hydrate for use as a natural gas resource. Small pores in fine-grained shaley intervals are shown to significantly increase the aqueous solubility of methane in pore water relative to surrounding coarser-grained sediment strata, which can have broad implications for methane hydrate formation, including lack of formation in the clayey intervals and strong diffusive fluxes of methane into coarser sediment layers. Finally, an existing methane hydrate reservoir simulator is modified to model methane hydrate accumulations in marine environments with heterogeneous layered sediments. The impact of pore size on solubility is included in the model along with steady state microbial methanogenesis and diffusion of salt in the pore water. The simulator is then used to successfully model methane hydrate accumulations in 1D and 2D at Walker Ridge Site 313 in the Gulf of Mexico, where well logs and seismic surveys throughout the region abound. This work is an important step in building a general 3D methane hydrate reservoir simulator for shallow marine environments around the globe.Item Effect of a discrete three-phase methane equilibrium zone on the bottom-simulating reflection(2016-12) Shushtarian, Arash; Daigle, HughMarine gas hydrates are stable under conditions of low temperature and high pressure in the upper few hundreds of meters below the seafloor in a variety of geological setting. At a discrete horizon where thermodynamically favored phase switches from hydrate to gas, a characteristic seismic reflection referred as the bottom-simulating reflection (BSR) is produced. Furthermore, in sediments with a distribution of pore sizes, the gas and hydrate phases can coexist in pores of different sizes, giving a rise to three-phase equilibrium zone. This three-phase zone causes the BSR to have distinct characteristics that differ from those observed with a discrete phase boundary. The main objective of this thesis is to model the seismic response of a potential three-phase zone at the Walker Ridge Block 313H in the northern Gulf of Mexico. I modeled the BSR arising from this three-phase zone and analyzed the characteristics of the BSR and their relationships to the thickness and phase saturation within the three-phase zone. This was done by determining the elastic properties of the formation via rock physics models and their mathematical convolution with a seismic wavelet to create synthetic seismograms. Results show that the main factor for the intensity of the BSR is the abundance of the free gas in the three-phase zone. Free gas saturation as low as 5% in the three-phase zone is enough to make the BSR visible in synthetic seismograms regardless of the hydrate saturation. Results of this thesis are significant for resource prospecting based on seismic data, drilling hazard identification, as well as the importance of hydrate as a potential source of energy and its influence on the global climate. For seismic prospecting, the presence of a three-phase zone inferred from BSR characteristic indicates the minimum methane flux into the base of the hydrate stability zone, and can be used to infer whether sufficient methane is available to form hydrate. For drilling hazard identification, the BSR characteristic indicates a possible shallower occurrence of gas than would be estimated under the assumption of a discrete phase boundary.Item Effect of surfactants on methane hydrate formation and dissociation(2011-05) Ramaswamy, Divya; Sharma, Mukul M.; Bryant, Steven L.Dissociation of gas hydrates has been the primary concern of the oil and gas industry for flow assurance, mainly in an offshore environment. There is also a growing interest in the rapid formation of gas hydrates for gas storage, transport of natural gas and carbon sequestration. In this thesis, we experimentally measure the kinetics of formation and dissociation of methane hydrates and the effect of various anionic and cationic surfactants such as sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB) and alpha olefin sulfonate (AOS) on the association/dissociation rate constants. The importance and necessity of micelle formation in these surfactants has been studied. The effect of foam generation on the rate of formation of these hydrates has also been measured. SDS was found to significantly decrease the induction time for hydrate formation. There was an added decrease in the induction time when a foamed mixture of water and SDS was used. On the other hand CTAB and AOS had an inhibiting effect. The contribution of micelles towards promoting hydrate formation was demonstrated with a series of experiments using SDS. The micelles formed by these surfactants appear to serve as nucleation sites for the association of hydrates. New experimental data is presented to show that some surfactants and the use of foam can significantly increase the rate of hydrate formation. Other surfactants are shown to act as inhibitors. A new experimental setup is presented that allows us to distinguish between surfactants that act as promoters and inhibitors for hydrate formation.