Natural gas hydrate deposits: a review of in situ properties

Pearson, Chris; Halleck, P.M.; McGuire, P.L.; Hermes, R.; Mathews, Mark

doi:10.1021/j100244a041

Cited by 179 publications

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“…They further assumed that n = m, which simplifies the Archie function. These values of a and m are also similar to those found for deep sea sediment cores from elsewhere (e.g., Wang et al, 1976;Pearson et al, 1983).…”

Section: Leg 146 Resistivity and Porosity Datasupporting

confidence: 84%

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Gas hydrate concentration estimates from chlorinity, electrical resistivity and seismic velocity

Riedel

Collett²,

Hyndman

2005

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Gas hydrate beneath the N. Cascadia continental slope off Vancouver Island occurs as a regional diffuse layer above the BSR and as local high concentrations in large vent or upwelling structures. Regional concentrations of gas hydrate beneath the N. Cascadia continental slope off Vancouver Island have been estimated earlier using multichannel seismic, seafloor electrical, and IODP Leg 146 downhole data. The concentrations of between 15 and 30% of pore saturation in a 100 m thick layer above the BSR are much higher than estimated elsewhere where there is good data, especially the Blake Ridge and central Cascadia off Oregon on ODP Leg 204. Although both of these other studies involved different sediment environments, a careful re-evaluation of the N. Cascadia estimates seemed desirable. We have re-evaluated the methods used to calculate the gas hydrate concentrations from pore-water chlorinity (salinity), electrical resistivity, and seismic velocity, describing in detail the assumptions and uncertainties. Use of the porewater chlorinity/salinity and electrical resistivity directly have low reliability because of the effect on the no-hydrate reference of hydrate formation and dissociation, and the effect of pore fluid freshening by clay dehydration. At ODP Site 889/890 hydrate concentrations range from 5-10% to 30-40%, depending on the no-hydrate reference salinity used. Use of core salinity data along with the downhole and seafloor electrical resistivity data allows calculation of both the in situ reference salinity and the hydrate concentrations. The most important uncertainty in this method is the relation between 2 resistivity and porosity, i.e., Archie's Law parameters. Significantly different relations were determined from the ODP Leg 146 core and downhole log data, the log data resistivity-porosity relation giving much lower concentrations. Finally, seismic velocities from sonic-logs and multichannel data can be used to calculate gas hydrate concentrations, if an appropriate no-hydrate velocity-depth profile can be estimated. A velocity-hydrate concentration relation is also required. Depending on which nohydrate/no-gas velocity baseline is used, estimated hydrate concentrations range from as low as 5% to above 25% saturation. In spite of having three nearly independent methods of estimating hydrate concentrations, it is concluded that the data allow regional concentrations in the 100 m layer above the BSR from less than 5% to over 25% saturation (3-13% of sediment volume). ODP drilling in the region scheduled for the fall of 2005 should help resolve the uncertainties.

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Section: Leg 146 Resistivity and Porosity Datasupporting

confidence: 84%

“…The parameter n (also called saturation exponent) can be estimated by averaging values for different lithologies (Pearson et al, 1983). A value of 1.94 was for example calculated as a pooled estimate for Site 889 (Collett, 2000).…”

Section: Saturation Exponent Nmentioning

confidence: 99%

Gas hydrate concentration estimates from chlorinity, electrical resistivity and seismic velocity

Riedel

Collett²,

Hyndman

2005

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“…The measured conductivity drops as the conductivity probe penetrates the core and the probe tip transitions from being surrounded by a conductive pressurization fluid to being increasingly surrounded by low-conductivity material. Conductivity can drop further in high-S h silty-sands where conductive pore fluid is replaced by insulative gas hydrate (Lee et al, 2010b;Pearson et al, 1983;Spangenberg and Kulenkampff, 2006).…”

Section: Electrical Conductivitymentioning

confidence: 99%

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Santamarina

Dai

Terzariol

et al. 2015

Marine and Petroleum Geology

191

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a b s t r a c tNatural hydrate-bearing sediments from the Nankai Trough, offshore Japan, were studied using the Pressure Core Characterization Tools (PCCTs) to obtain geomechanical, hydrological, electrical, and biological properties under in situ pressure, temperature, and restored effective stress conditions. Measurement results, combined with index-property data and analytical physics-based models, provide unique insight into hydrate-bearing sediments in situ. Tested cores contain some silty-sands, but are predominantly sandy-and clayey-silts. Hydrate saturations S h range from 0.15 to 0.74, with significant concentrations in the silty-sands. Wave velocity and flexible-wall permeameter measurements on neverdepressurized pressure-core sediments suggest hydrates in the coarser-grained zones, the silty-sands where S h exceeds 0.4, contribute to soil-skeletal stability and are load-bearing. In the sandy-and clayey-silts, where S h < 0.4, the state of effective stress and stress history are significant factors determining sediment stiffness. Controlled depressurization tests show that hydrate dissociation occurs too quickly to maintain thermodynamic equilibrium, and pressureetemperature conditions track the hydrate stability boundary in pure-water, rather than that in seawater, in spite of both the in situ pore water and the water used to maintain specimen pore pressure prior to dissociation being saline. Hydrate dissociation accompanied with fines migration caused up to 2.4% vertical strain contraction. The firstever direct shear measurements on never-depressurized pressure-core specimens show hydratebearing sediments have higher sediment strength and peak friction angle than post-dissociation sediments, but the residual friction angle remains the same in both cases. Permeability measurements made before and after hydrate dissociation demonstrate that water permeability increases after dissociation, but the gain is limited by the transition from hydrate saturation before dissociation to gas saturation after dissociation. In a proof-of-concept study, sediment microbial communities were successfully extracted and stored under high-pressure, anoxic conditions. Depressurized samples of these extractions were incubated in air, where microbes exhibited temperature-dependent growth rates.Published by Elsevier Ltd.

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“…where 1.19386 is an empirical constant determined by Pearson et al [1983] and R(z) is the deep resistivity recorded with the array induction tool (AIT). The gamma ray log shows that in the hydratebearing intervals the lithology is generally similar to the formation above 900 m, indicating that the baseline is a valid reference to estimate hydrate saturation in these intervals without correcting for lithology.…”

Section: Logging Datamentioning

confidence: 99%

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

2002

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[1] The Mallik 2L-38 research well was drilled to 1150 m under the Mackenzie Delta, Canada, and penetrated a subpermafrost interval where methane hydrate occupies up to 80% of the pore space. A suite of high-quality downhole logs was acquired to measure in situ the physical properties of these hydrate-bearing sediments. Similar to other hydrate deposits, resistivity and compressional and shear sonic velocity data increase with higher hydrate saturation owing to electrical insulation of the pore space and stiffening of the sediment framework. In addition, sonic waveforms show strong amplitude losses of both compressional and shear waves in intervals where methane hydrate is observed. We use monopole and dipole waveforms to estimate compressional and shear attenuation. Comparing with hydrate saturation values derived from the resistivity log, we observe a linear increase in both attenuation measurements with increasing hydrate saturation, which is not intuitive for stiffening sediments. Numerical modeling of the waveforms allows us to reproduce the recorded waveforms and illustrate these results. We also use a model for wave propagation in frozen porous media to explain qualitatively the loss of sonic waveform amplitude in hydratebearing sediments. We suggest that this model can be improved and extended, allowing hydrate saturation to be quantified from attenuation measurements in similar environments and providing new insight into how hydrate and its sediment host interact.

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Natural gas hydrate deposits: a review of in situ properties

Abstract: The presence of hydrates also tends to lower the heat capacities ties of sediments, but these effects are coinparative'ysmall and not useful for exploration.

Cited by 179 publications

References 0 publications

Gas hydrate concentration estimates from chlorinity, electrical resistivity and seismic velocity

Gas hydrate concentration estimates from chlorinity, electrical resistivity and seismic velocity

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

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