HAL : insu-00627726, version 1

DOI : 10.1029/2010GC003381

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Geochemistry Geophysics Geosystems 12 (2011) 1-17

Interpretation of porosity and LWD resistivity from the Nankai accretionary wedge in light of clay physicochemical properties: Evidence for erosion and local overpressuring

Marianne Conin 1, P. Henry 1, S. Bourlange 2, Hugues Raimbourg 3, Thierry Reuschlé 4

(2011)

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.

1 :	Centre européen de recherche et d'enseignement de géosciences de l'environnement (CEREGE)
	CNRS : UMR7330 – Institut de recherche pour le développement [IRD] – INSU – Aix-Marseille Université - AMU
2 :	Centre de recherches petrographiques et géochimiques (CRPG)
	CNRS : UPR2300 – INSU
3 :	Institut des Sciences de la Terre d'Orléans (ISTO)
	Université d'Orléans – CNRS : UMR6113 – Université François Rabelais - Tours – INSU
4 :	Institut de physique du globe de Strasbourg (IPGS)
	CNRS : UMR7516 – INSU – Université de Strasbourg

Équipe de recherche : GE

domaine

:

Planète et Univers/Sciences de la Terre/Tectonique Sciences de l'environnement/Milieux et Changements globaux

mots-clés : accretionary wedge – porosity – resistivity model – compaction – erosion – overpressure.

insu-00627726, version 1

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Contributeur : Nathalie Pothier <>

Soumis le : Jeudi 29 Septembre 2011, 14:35:11

Dernière modification le : Mardi 7 Mai 2013, 16:23:14