GEOSCAN, résultats de la recherche


TitreLarge-scale depositional characteristics of the Ulleung Basin and its impact on electrical resistivity and Archie-parameters for gas hydrate saturation estimates
AuteurRiedel, M; Collett, T S; Kim, H -S; Bahk, J -J; Kim, J -H; Ryu, B -J; Kim, G Y
SourceMarine and Petroleum Geology vol. 47, 2013 p. 222-235,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120307
ÉditeurElsevier BV
Documentpublication en série
Mediapapier; en ligne; numérique
Lat/Long OENS130.0000 132.0000 37.5000 36.0000
Sujetsgaz; hydrate; hydrocarbures; gaz d'hydrocarbure; gaz d'origine biologique; géologie marine; combustibles fossiles
Illustrationslocation maps; plots; tables; profiles
ProgrammeHydrates de gaz, Caractérisation des Hydrates de gaz
Résumé(disponible en anglais seulement)
Gas hydrate saturation estimates were obtained from an Archie-analysis of the Logging-while-drilling (LWD) electrical resistivity logs under consideration of the regional geological framework of sediment deposition in the Ulleung Basin, East Sea, off Korea. Porosity was determined from the LWD bulk density log and core-derived values of grain density. In situ measurements of pore-fluid salinity as well as formation temperature define a background trend for pore-fluid resistivity at each drill site. The LWD data were used to define sets of empirical Archie-constants for different depth-intervals of the logged borehole at all sites drilled during the Ulleung Basin Gas Hydrate Expedition 2 (UBGH2). A clustering of data with distinctly different trend-lines is evident in the cross-plot of porosity and formation factor for all sites drilled during UBGH2. The reason for the clustering is related to the difference between hemipelagic sediments (mostly covering the top ~100 mbsf) and mass-transport deposits (MTD) and/or the occurrence of biogenic opal. For sites located in the north-eastern portion of the Ulleung Basin a set of individual Archie-parameters for a shallow depth interval (hemi-pelagic) and a deeper zone (MTD) was achieved. The deeper zone shows typically higher resistivities for the same range of porosities seen in the upper zone, reflecting a shift in sediment properties. The presence of large amounts of biogenic opal (up to and often over 50% as defined by XRD data) was especially observed at Sites UBGH2-2 1 and UBGH2-2 2 (as well as UBGH1-9 from a previous drilling expedition in 2007). The boundary between these two zones can also easily be identified in gamma-ray logs, which also show unusually low readings in the opal-rich interval. Only by incorporating different Archie-parameters for the different zones a reasonable estimate of gas hydrate saturation was achieved that also matches results from other techniques such as pore-water freshening, velocity-based calculations, and pressure-core degassing experiments. Seismically, individual boundaries between zones were determined using a grid of regional 2D seismic data. Zoning from the Archie-analysis for sites in the south-western portion of the Ulleung Basin was also observed, but at these sites it is linked to individually stacked mass-transport deposits (MTDs) only and does not reflect a mineralogical occurrence of biogenic opal or hemi-pelagic sedimentation. The individual MTD events represent differently compacted material often associated with a strong decrease in porosity (and increase in density), warranting a separate set of empirical Archie-parameters.