Journal Article

Characterizing electrical properties and permeability changes of hydrate bearing sediments using ERT data

Mike Priegnitz, Jan Thaler, Erik Spangenberg, Judith M. Schicks, Jörg Schrötter and Sven Abendroth

in Geophysical Journal International

Volume 202, issue 3, pages 1599-1612
ISSN: 0956-540X
Published online July 2015 | e-ISSN: 1365-246X | DOI: https://dx.doi.org/10.1093/gji/ggv245

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A LArge Reservoir Simulator (LARS) was equipped with an electrical resistivity tomography (ERT) array to monitor hydrate formation and dissociation experiments. During two hydrate formation experiments reaching 90 per cent bulk hydrate saturation, frequent measurements of the electrical properties within the sediment sample were performed. Subsequently, several common mixing rules, including two different interpretations of Archie's law, were tested to convert the obtained distribution of the electrical resistivity into the spatial distribution of local hydrate saturation. It turned out that the best results estimating values of local hydrate saturation were obtained using the Archievarphi approach where the increasing hydrate phase is interpreted as part of the sediment grain framework reducing the sample's porosity. These values of local hydrate saturation were used to determine local permeabilities by applying the Carman-Kozeny relation. The formed hydrates were dissociated via depressurization. The decomposition onset as well as areas featuring hydrates and free gas were inferred from the ERT results. Supplemental consideration of temperature and pressure data granted information on discrete areas of hydrate dissociation.

Keywords: Tomography; Electrical properties; Gas and hydrate systems; Permeability and porosity

Journal Article.  9814 words.  Illustrated.

Subjects: Geophysics ; Oceanography and Hydrology