Data report: permeability and microfabric of core samples from IODP Expedition 348, Hole C0002P, Nankai Trough accretionary prism

Abstract

This report documents the results of constant-flow permeability tests in the vertical (along core) direction administered at effective isotropic confining stresses of 0.28 MPa (40 psi) and 0.55 MPa (80 psi). Specimens from the Nankai accretionary prism were collected from Hole C0002P of the Integrated Ocean Drilling Program. Beds dip at steep angles (typically 80° or more) throughout the cored interval (2174.98-2209.64 meters below seafloor). We tested specimens that consist of indurated clayey siltstone and medium to coarse siltstone. Environmental scanning electron microscopy shows that grain fabric is random and does not vary significantly among the specimens tested. Hydraulic conductivity values range from 3.83 × 10 -9 to 2.68 × 10 -8 cm/s. Intrinsic permeability values range from 3.80 × 10 -18 to 2.66 × 10 -17 m 2 . IntroductionThe primary objective of Integrated Ocean Drilling Program (IODP) Expedition 348 was to characterize the variations of lithology and structure at intermediate depths of the Nankai Trough accretionary prism (offshore southwest Japan). Site C0002 (Fig. F1) is located on the upper plate of the subduction zone above the seismogenic (presumably locked) portion of the plate boundary thrust system (see the "Expedition 348 summary" chapter [Tobin et al., 2015a]). The long-term goal of deeper drilling at this site is to cross the megasplay at seismogenic depths where coseismic slip occurred during the 1944 Tonankai earthquake (Ichinose et al., 2003). During Expedition 348, IODP collected a full suite of logging-while-drilling data, cuttings at ~5 m intervals, and cores over a 55.5 m interval from 2163 to 2218.5 meters below seafloor (mbsf). The cores are the deepest ever recovered from an active accretionary prism.Intrinsic permeability (k) and hydraulic conductivity (K) values for natural clay-rich sediment and sedimentary rock (e.g., Neuzil, 1994;Aplin et al., 2006; Gamage et al., 2011) typically span several orders of magnitude. That natural variability exists because their hydrogeological properties depend on many factors, some of which are inherited from the time of mud deposition. Grain size and shape, sorting, particle orientation, surface charges on clay particles, and microfabric are important, as are the superimposed effects of burial diagenesis (e.g., Moon and Hurst, 1984;Bennett et al., 1989).The cores from Hole C0002P contain numerous layers and irregular lenses of fine sand-and siltstone, with thicknesses ranging from laminae (millimeter scale) to ~20 cm. Those coarser textures should increase values of permeability. Furthermore, the strata dip steeply over the cored interval, typically at angles >80° (see the "Expedition 348 summary" chapter [Tobin et al., 2015a]). Those orientations should alter the anisotropy of permeability (i.e., horizontal versus vertical) relative to a normally compacted sedimentary basin. Our study contributes new data to the transect-wide Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), thereby allowing for hydrogeological comparisons ...

In Situ Permeability and Scale Dependence of an Active Accretionary Prism Determined From Cross‐Borehole Experiments

“…Scale dependence of permeability in the Nankai accretionary prism. Permeabilities estimated from several methods and scales are shown, including: laboratory experiments (gray circles; Takahashi et al, 2013;Song & Underwood, 2017;Valdez (2018, supporting information), single probe Modular Formation Dynamics Tester test (green square; Saffer et al, 2013), drawdown (DD; yellow diamond) and hydraulic fracture (HF; white diamond) Modular Formation Dynamics Tester tests; Boutt et al, 2012), tidal loading response (purple star; Kinoshita et al, 2017), and cross-hole test analysis (this study; triangles). Gray area shows range of fault zone permeabilities from inverse modeling studies at several subduction margins (Saffer, 2015).…”

“…Takahashi et al () conducted triaxial experiments on core samples of the accretionary prism from Site C0002 and measured permeabilities of 2.9 × 10 −19 to 2.3 × 10 −18 m 2 under estimated in situ pressure conditions (effective stress of 7.9–9.0 MPa). Song and Underwood () reported values of 4.3 × 10 −18 to 2.7 × 10 −17 m 2 from constant‐flow tests on core samples conducted at room temperature and at effective stresses of 0.28 MPa. Valdez (, supporting information) obtained permeabilities of 2.5 × 10 −18 to 5.3 × 10 −17 m 2 for core samples of the accretionary prism from Site C0009, at effective stresses of 11–12 MPa.…”

Effective Porosity Profile at IODP Site C0002 in the Heart of the Nankai Accretionary Prism, and Its Use for Predicting In Situ Seismic Velocities

“…The Katz‐Thompson permeability (Katz & Thompson, 1986, 1987) of the sample from Hole C0002R is ∼3 × 10 −19 m 2 , which is 2 orders of magnitude lower than reported by Song and Underwood (2017) at ∼2,200 mbsf based on constant‐flow permeability tests.…”