Detection of gas hydrate with downhole logs and assessment of gas hydrate concentrations (saturations) and gas volumes on the Blake Ridge with electrical resistivity log data

Collett, Timothy S.; Ladd, John W.

doi:10.2973/odp.proc.sr.164.219.2000

Cited by 158 publications

(167 citation statements)

References 11 publications

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“…Procedures followed standard Archie analyses (Archie, 1942;Collett and Ladd, 2000), and a detailed description of the methods and assumptions involved can be found in the "Methods" chapter. More detailed analyses of gas hydrate concentrations from the downhole resistivity log data were conducted after the expedition by Malinverno et al (2008) and Chen et al Malinverno et al (2008) presented a method to calculate gas hydrate concentrations from the direct comparison of core-derived salinity and downhole log data from Site U1325 that honors the spatial uncertainty in the measurements from different boreholes located ~25 m apart.…”

Section: Gas Hydrate Concentration Estimatesmentioning

confidence: 99%

Expedition 311 Synthesis: scientific findings

Riedel¹,

Collett²,

Malone³

2010

Proceedings of the IODP

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Integrated Ocean Drilling Program Expedition 311 was conducted to study gas hydrate occurrences and their evolution along a transect spanning the entire northern Cascadia accretionary margin. A transect of four research sites (U1325, U1326, U1327, and U1329) was established over a distance of 32 km, extending from Site U1326 near the deformation front to Site U1329 at the eastern limit of the inferred gas hydrate occurrence zone. In addition to the transect, a fifth site (U1328) was established at a cold vent setting with active fluid and gas expulsion, which provided an opportunity to compare regional pervasive fluid-flow regimes to a site of focused fluid advection. In this synthesis, a revised gas hydrate formation model is proposed based on a combination of geophysical, geochemical, and sedimentological data acquired during and after Expedition 311 and from previous studies. The main elements of this revised model are as follows:1. Fluid expulsion by tectonic compression of accreted sediments at nonuniform expulsion rates along the transect results in the evolution of variable pore water regimes across the margin. Sites closer to the deformation front are characterized by pore fluids enriched in dissolved salts at depth, where zeolite formation from ash diagenesis is dominant. In contrast, the landward portion of the margin shows a freshening of pore fluids with depth as a result of the progressive overprinting of diagenetic salt generation with freshwater generation from the smectite-to-illite transition at greater depth. 2. In situ methane produced by microbial CO 2 reduction within the gas hydrate stability zone is the prevalent gas source for gas hydrate formation. 3. Some minor methane advection from depth is required overall to explain the occurrence of gas hydrate (and the associated downhole isotopic signatures of CH 4 and CO 2 ) within the sediments of the accretionary prism and the absence of gas hydrate within the abyssal plain sediments. In contrast, methane migrating from depth is a dominant source for gas hydrate formation at the cold vent Site U1328 (Bullseye vent). 4. Gas hydrate preferentially forms in coarser grained sandy/silt turbidites, resulting in very high local gas hydrate concentrations. Typically, gas hydrate occupies <5% of the pore space throughout the gas hydrate stability zone. Higher gas hydrate saturations were observed in intervals with abundant coarse-

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Section: Gas Hydrate Concentration Estimatesmentioning

confidence: 99%

Expedition 311 Synthesis: scientific findings

Riedel¹,

Collett²,

Malone³

2010

Proceedings of the IODP

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“…These compounds are metastable and exist only under certain pressure and temperature conditions which exist naturally in deep marine sediments and in polar regions where permafrost is present. The estimated global volume of methane stored in hydrate ranges from 2 to 4 Â 10 16 m 3 at STP (temperature of 273.15 K and pressure of 101.325 kPa) [Kvenvolden, 1988] which, combined with its metastability, has led to hydrates becoming of international importance with regard to: their potential as a future energy resource [Collett and Ladd, 2000;Kvenvolden, 1998]; their role in global warming [Haq, 1998]; and their potential as a geotechnical hazard [Ashi, 1999;Berndt et al, 2002;Kayen and Lee, 1991;Mienert et al, 1998;Popenoe et al, 1993].…”

Section: Nature and Distribution Of Marine Gas Hydratesmentioning

confidence: 99%

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

2005

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[1] Remote seismic methods, which measure the compressional wave (P wave) velocity (V p ) and shear wave (S wave) velocity (V s ), can be used to assess the distribution and concentration of marine gas hydrates in situ. However, interpreting seismic data requires an understanding of the seismic properties of hydrate-bearing sediments, which has proved problematic because of difficulties in recovering intact hydrate-bearing sediment samples and in performing valid laboratory tests. Therefore a dedicated gas hydrate resonant column (GHRC) was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both V p and V s made at frequencies and strains relevant to marine seismic investigations. Thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested. The results show a bipartite relationship between velocities and hydrate pore saturation, with a marked transition between 3 and 5% hydrate pore saturation for both V p and V s . This suggests that methane hydrate initially cements sand grain contacts then infills the pore space. These results show in detail for the first time, using a resonant column, how hydrate cementation affects elastic wave properties in quartz sand. This information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation.Citation: Priest, J. A., A. I. Best, and C. R. I. Clayton (2005), A laboratory investigation into the seismic velocities of methane gas hydrate-bearing sand,

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“…Gas hydrate concentrations may be estimated from downhole electrical resistivity (e.g., Collett and Ladd, 2000;Hyndman et al, 1999) because, compared to the saline pore water, gas hydrate is a nearly perfect insulator. The resistivity from downhole logs in the Cascadia Basin Site 888 is ~1.0 Ωm to a depth of several hundred meters, typical of deep-sea oceanbottom sediments.…”

Section: Electrical Resistivitymentioning

confidence: 99%

Gas hydrate on the northern Cascadia margin: regional geophysics and structural framework

Riedel¹,

Willoughby²,

Chen³

et al. 2006

Proceedings of the IODP

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Integrated Ocean Drilling Program Expedition 311 is based on extensive site survey data and historic research at the northern Cascadia margin since 1985. This research includes various regional geophysical surveys using a broad spectrum of seismic techniques, coring and logging by the Ocean Drilling Program Leg 146, heat flow measurements, shallow piston coring, and bottom video observations across a cold-vent field, as well as novel controlled-source electromagnetic and seafloor compliance surveying techniques. The wealth of data available allowed construction of structural cross-sections of the margin, development of models for the formation of gas hydrate in an accretionary prism, and estimation of gas hydrate and free gas concentrations. Expedition 311 established for the first time a transect of drill sites across the northern Cascadia margin to study the evolution of gas hydrate formation over the entire gas hydrate stability field of the accretionary complex. This paper reviews the tectonic framework at the northern Cascadia margin and summarizes the scientific studies that led to the drilling objectives of Expedition 311 Cascadia gas hydrate.

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Detection of gas hydrate with downhole logs and assessment of gas hydrate concentrations (saturations) and gas volumes on the Blake Ridge with electrical resistivity log data

Cited by 158 publications

References 11 publications

Expedition 311 Synthesis: scientific findings

Expedition 311 Synthesis: scientific findings

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

Gas hydrate on the northern Cascadia margin: regional geophysics and structural framework

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