Physical Chemical Characteristics of Natural Gas Hydrate

Osegovic, John P.; Tatro, Shelli R.; Holman, Sarah A.

doi:10.1007/1-4020-3972-7_3

Cited by 12 publications

(5 citation statements)

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“…The sample is repressurized with methane gas before the dissociation front reaches the sample's central axis. Hydrate persisting near the sample's central axis forms a surface for rapid growth of new hydrate following the repressurization step [ Osegovic et al , 2006]. Capillary forces draw water to the hydrate formation front [ Gupta et al , 2006; Kneafsey et al , 2007] (Figure 4c), reducing the water available for hydrate formation near the sample perimeter.…”

Section: Laboratory Results For Gas‐rich Methane Hydrate‐bearing Sedmentioning

confidence: 99%

Physical property changes in hydrate‐bearing sediment due to depressurization and subsequent repressurization

et al. 2008

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[1] Physical property measurements of sediment cores containing natural gas hydrate are typically performed on material exposed, at least briefly, to non-in situ conditions during recovery. To examine the effects of a brief excursion from the gas-hydrate stability field, as can occur when pressure cores are transferred to pressurized storage vessels, we measured physical properties on laboratory-formed sand packs containing methane hydrate and methane pore gas. After depressurizing samples to atmospheric pressure, we repressurized them into the methane-hydrate stability field and remeasured their physical properties. Thermal conductivity, shear strength, acoustic compressional and shear wave amplitudes, and speeds of the original and depressurized/repressurized samples are compared. X-ray computed tomography images track how the gas-hydrate distribution changes in the hydrate-cemented sands owing to the depressurizaton/repressurization process. Because depressurization-induced property changes can be substantial and are not easily predicted, particularly in water-saturated, hydrate-bearing sediment, maintaining pressure and temperature conditions throughout the core recovery and measurement process is critical for using laboratory measurements to estimate in situ properties.

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Section: Laboratory Results For Gas‐rich Methane Hydrate‐bearing Sedmentioning

confidence: 99%

Physical property changes in hydrate‐bearing sediment due to depressurization and subsequent repressurization

et al. 2008

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“…The following processes develop as temperature increases (refer to Figure 1). [8] In the absence of hydrates, gas solubility in water increases as temperature decreases and pressure increases, as prescribed in Henry's law [Lide, 1997;Osegovic et al, 2006]. The presence of hydrates facilitates further hydrate formation, and hence the equilibrium concentration of gas in water decreases and gas solubility in water increases with temperature [Handa, 1990;Aya et al, 1997;Davie et al, 2004;Servio and Englezos, 2001;Duan and Mao, 2006]; this observation applies to the A-B path in the stability ''H + L w '' zone in Figure 1.…”

Section: Underlying Processesmentioning

confidence: 95%

Gas hydrate dissociation in sediments: Pressure‐temperature evolution

Kwon

Cho

Santamarina

2008

Geochem Geophys Geosyst

111

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[1] Hydrate-bearing sediments may destabilize spontaneously as part of geological processes, unavoidably during petroleum drilling/production operations or intentionally as part of gas extraction from the hydrate itself. In all cases, high pore fluid pressure generation is anticipated during hydrate dissociation. A comprehensive formulation is derived for the prediction of fluid pressure evolution in hydrate-bearing sediments subjected to thermal stimulation without mass transfer. The formulation considers pressure-and temperature-dependent volume changes in all phases, effective stress-controlled sediment compressibility, capillarity, and the relative solubilities of fluids. Salient implications are explored through parametric studies. The model properly reproduces experimental data, including the PT evolution along the phase boundary during dissociation and the effect of capillarity. Pore fluid pressure generation is proportional to the initial hydrate fraction and the sediment bulk stiffness; is inversely proportional to the initial gas fraction and gas solubility; and is limited by changes in effective stress that cause the failure of the sediment. When the sediment stiffness is high, the generated pore pressure reflects thermal and pressure changes in water, hydrate, and mineral densities. Comparative analyses for CO 2 and CH 4 highlight the role of gas solubility in excess pore fluid pressure generation. Dissociation in small pores experiences melting point depression due to changes in water activity, and lower pore fluid pressure generation due to the higher gas pressure in small gas bubbles. Capillarity effects may be disregarded in silts and sands, when hydrates are present in nodules and lenses and when the sediment experiences hydraulic fracture.

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“…Gas solubility in water in the absence of hydrates. The pressure and temperature PT dependent gas concentration in water M P,T [mol/m 3 ] can be approximated using Henry's law as a linear function of pressure P: [Osegovic et al 2006;Wilhelm et al 1977]. Hence, the solubility of CH 4 and CO 2 in water rises with increasing pressure and decreasing temperature.…”

Section: Gas Solubilitymentioning

confidence: 99%

Hydrate bearing clayey sediments: Formation and gas production concepts

Jang

Santamarina

2016

Marine and Petroleum Geology

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Hydro-thermo-chemo and mechanically coupled processes determine hydrate morphology and control gas production from hydrate-bearing sediments. Force balance, together with mass and energy conservation analyses anchored in published data provide robust asymptotic solutions that reflect governing processes in hydrate systems. Results demonstrate that hydrate segregation in clayey sediments results in a two-material system whereby hydrate lenses are surrounded by hydrate-free water-saturated clay. Hydrate saturation can reach 2% by concentrating the excess dissolved gas in the pore water and 20% from metabolizable carbon. Higher hydrate saturations are often found in natural sediments and imply methane transport by advection or diffusion processes. Hydrate dissociation is a strongly endothermic event; the available latent heat in a reservoir can sustain significant hydrate dissociation without triggering ice formation during depressurization. The volume of hydrate expands 2-to-4 times upon dissociation or CO 2-CH 4 replacement. Volume expansion can be controlled to maintain lenses open and to create new open mode discontinuities that favor gas recovery. Pore size is the most critical sediment parameter for hydrate formation and gas recovery and is controlled by the smallest grains in a sediment. Therefore any characterization must carefully consider the amount of fines and their associated mineralogy.

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Physical Chemical Characteristics of Natural Gas Hydrate

Cited by 12 publications

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Physical property changes in hydrate‐bearing sediment due to depressurization and subsequent repressurization

Physical property changes in hydrate‐bearing sediment due to depressurization and subsequent repressurization

Gas hydrate dissociation in sediments: Pressure‐temperature evolution

Hydrate bearing clayey sediments: Formation and gas production concepts

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