An effective medium inversion algorithm for gas hydrate quantification and its application to laboratory and borehole measurements of gas hydrate-bearing sediments Chand, Shyam Minshull, Tim A. Priest, Jeff A. Best, Angus I. Clayton, Christopher R. I. Waite, William F. 2007-08-14T14:30:55Z 2007-08-14T14:30:55Z 2006-07-04
dc.description Author Posting. © Blackwell, 2006. This article is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 166 (2006): 543–552, doi:10.1111/j.1365-246X.2006.03038.x. en
dc.description.abstract The presence of gas hydrate in marine sediments alters their physical properties. In some circumstances, gas hydrate may cement sediment grains together and dramatically increase the seismic P- and S-wave velocities of the composite medium. Hydrate may also form a load-bearing structure within the sediment microstructure, but with different seismic wave attenuation characteristics, changing the attenuation behaviour of the composite. Here we introduce an inversion algorithm based on effective medium modelling to infer hydrate saturations from velocity and attenuation measurements on hydrate-bearing sediments. The velocity increase is modelled as extra binding developed by gas hydrate that strengthens the sediment microstructure. The attenuation increase is modelled through a difference in fluid flow properties caused by different permeabilities in the sediment and hydrate microstructures. We relate velocity and attenuation increases in hydrate-bearing sediments to their hydrate content, using an effective medium inversion algorithm based on the self-consistent approximation (SCA), differential effective medium (DEM) theory, and Biot and squirt flow mechanisms of fluid flow. The inversion algorithm is able to convert observations in compressional and shear wave velocities and attenuations to hydrate saturation in the sediment pore space. We applied our algorithm to a data set from the Mallik 2L–38 well, Mackenzie delta, Canada, and to data from laboratory measurements on gas-rich and water-saturated sand samples. Predictions using our algorithm match the borehole data and water-saturated laboratory data if the proportion of hydrate contributing to the load-bearing structure increases with hydrate saturation. The predictions match the gas-rich laboratory data if that proportion decreases with hydrate saturation. We attribute this difference to differences in hydrate formation mechanisms between the two environments. en
dc.description.sponsorship This work was funded by European Commission under the contract EVK3-CT-2000-00043 (HYDRATECH). JAP and AIB were partly funded by Natural Environment Research Council. en
dc.format.mimetype application/pdf
dc.identifier.citation Geophysical Journal International 166 (2006): 543–552 en
dc.identifier.doi 10.1111/j.1365-246X.2006.03038.x
dc.language.iso en_US en
dc.publisher Blackwell Publishing en
dc.subject Attenuation en
dc.subject Elastic wave theory en
dc.subject Gas hydrate en
dc.subject P waves en
dc.subject S waves en
dc.title An effective medium inversion algorithm for gas hydrate quantification and its application to laboratory and borehole measurements of gas hydrate-bearing sediments en
dc.type Article en
dspace.entity.type Publication
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