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ANAXIMANDER Report Summary

Project ID: EVK3-CT-2002-00068
Funded under: FP5-EESD
Country: Spain

Methods for studying the textural, physical, geotechnical, and compositional parameters of sediments containing gas hydrate

Four aspects of the use of sedimentological experiments for the study of sediments containing marine gas hydrate can be mentioned. The same aspects have been used for sediments non containing gas hydrate in order to establish and assess differences and the relative importance of quantifiable parameters from marine sediments. The four aspects are the following:

- Determination of textural parameters that favour gas hydrate presence, from grain size (gravel, sand, silt and clay) to statistical parameter aspects (mean, sorting, skewenes and kurtosis).

- Determination of three physical parameters of those sediments containing gas hydrates using a continuous, non-destructive high-resolution Multi-Sensor Core Logger (MSCL). The measured parameters include wet-bulk density (by Gamma Ray Attenuation, GRAPE), magnetic susceptibility (MS) and P-wave velocity

- Discrete measurements of geotechnical properties of sediments containing gas hydrate. The parameters comprise the following index properties: water content, grain density, porosity and undrained shear strength.

- Determination of sand fraction composition and calcium carbonate content. Composition of sand fraction was determined by visual identification and by counting 350 grains per sample with the aims of a binocular. The following grains were considered to identify in sediments containing gas hydrate: quartz, light minerals, pyrite, glauconite, rock fragments, and forams (well and bad/broken preserved).

The innovative aspects of this result are three:
- Definition of those useful quantificable parameters to be measured in sediments containing gas hydrate;
- Comparison of sediments containing and non-containing gas hydrate; and
- Relationship between physical/geotechnical properties and the sedimentary processes and Texture of marine sediments. The linkage between these properties is not necessarily straightforward and their correlation must be considered in the context of the type of measurement and its scale, and sedimentary environment.

Sedimentological methods are a widely used of approach for direct detection of gas hydrate in marine sediments. The fact that natural gas hydrate is affected by changes in pressure and temperature makes its observation very difficult under laboratory conditions. This fact increases the value of the results obtained from the natural conditions, because it provides ground truth measurements for constraining geological framework. Although this result focuses on sediments from mud volcanoes, many of the concepts/parameters will be able also to apply to marine sediments from other environments on the continental margins and abyssal plains.

The knowledge of sediments containing gas hydrate from mud vocalnoes has improve significantly after the set of measured parameters. In particular it may provide useful information for:
- Identification of hydrate and hydrate-berating sediment in other sedimentary environments and their distribution with depth

- Source area of the gas

- Conduits that supply fluid gas and gas into the hydrate stability zone

- Estimation of porosity and methane saturation.


Ercilla GEMMA, (Scientific Researcher)
Tel.: +34-93-2309500
Fax: +34-93-2309555
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