Conin, Marianne J. et al. (2011): Interpretation of porosity and LWD resistivity from the Nankai accretionary wedge in light of clay physicochemical properties; evidence for erosion and local overpressuring

Leg/Site/Hole:
IODP 314 C0001
IODP 315 C0001
Identifier:
2013-046507
georefid

10.1029/2010GC003381
doi

Creator:
Conin, Marianne J.
Universite Aix-Marseille III, CEREGE, Aix en Provence, France
author

Henry, Pierre
CNRS, France
author

Bourlange, S.
Orleans University, France
author

Raimbourg, Hugues
Institut de Physique du Globe de Strasbourg, France
author

Reuschle, T.
author

Identification:
Interpretation of porosity and LWD resistivity from the Nankai accretionary wedge in light of clay physicochemical properties; evidence for erosion and local overpressuring
2011
Geochemistry, Geophysics, Geosystems - G (super 3)
American Geophysical Union and The Geochemical Society, United States
12
In this study, we used porosity to assess the compaction state of the Nankai accretionary wedge sediments and any implications for stress and pore pressure. However, hydrous minerals affect porosity measurements, and accounting for them is essential toward defining the interstitial porosity truly representative of the compaction state. The water content of sediments was measured in core samples and estimated from logging data using a resistivity model for shale. We used the cation exchange capacity to correct the porosity data for the amount of water bound to clay minerals and to correct the porosity estimates for the surface conductivity of hydrous minerals. The results indicate that several apparent porosity anomalies are significantly reduced by this correction, implying that they are in part artifacts from hydrous minerals. The correction also improves the fit of porosity estimated from logging-while-drilling (LWD) resistivity data to porosity measured on cores. Low overall porosities at the toe of the accretionary wedge and in the splay fault area are best explained by erosion, and we estimated the quantity of sediments eroded within the splay fault area by comparing porosity-effective stress relationships of the sediments to a reference curve. Additionally, a comparison of LWD data with core data (resistivity and P wave velocity) obtained at Site C0001 landward of the mega-splay fault area, suggested a contribution from the fracture porosity to in situ properties on the formation.
Coverage:Geographic coordinates:
North:33.1400
West:136.4300East: 136.4300
South:33.1400

Oceanography; accretionary wedges; body waves; clastic sediments; clay; clay minerals; elastic waves; electrical conductivity; electrical methods; erosion; fractures; geophysical methods; Integrated Ocean Drilling Program; interpretation; IODP Site C0001; marine geology; measurement-while-drilling; Nankai Trough; NanTroSEIZE; North Pacific; Northwest Pacific; overpressure; P-waves; Pacific Ocean; permeability; physicochemical properties; porosity; resistivity; sediments; seismic waves; sheet silicates; silicates; velocity; well-logging; West Pacific;

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