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doi:10.2204/iodp.proc.314315316.214.2011

Results

Table T1 summarizes the values of gravimetric water content and porosity for trimmings measured before and after each constant flow–through test. The table also indicates average height and diameter of each specimen and backpressure saturation. The values of gravimetric water content and porosity differ from shipboard measurements but in an inconsistent manner. In cases where water content appears to decrease relative to shipboard values, these discrepancies may be due to partial loss of moisture during shipment and storage of the whole-round specimens. For one specimen (Sample 316-C0006E-7H-2, 117 cm), the value of porosity after the flow-through test is significantly greater than the value of porosity before the test. This could be a result of operator error and/or expansion of water-filled microcracks after the specimen was released from the confining pressure. It is important to note that the same specimen could not be trimmed for a test in the horizontal flow direction because of excessive fracturing. We consider the vertical test results to be unreliable for Sample 316-C0006E-7H-2, 117 cm. The data have been included in Table T2 but were omitted from the illustrations.

Table T2 summarizes the average values of vertical (kv) and horizontal (kh) permeability and the corresponding kh/kv ratio for each specimen. Volumetric flow rate (Q), discharge velocity (v), steady-state head loss (Δhs), steady-state hydraulic gradient (is), hydraulic conductivity (K), and intrinsic permeability (k) from four test runs conducted for each specimen at 0.55 MPa (80 psi) effective stress (σ′) are summarized in Table T3.

At Site C0006, the highest value of vertical hydraulic conductivity is 1.60 × 10–6 cm/s with corresponding intrinsic permeability of 1.63 × 10–15 m2. The lowest value of vertical hydraulic conductivity is 2.63 × 10–10 cm/s with intrinsic permeability equal to 2.68 × 10–19 m2. The highest value of horizontal hydraulic conductivity is 2.07 × 10–6 cm/s with intrinsic permeability equal to 2.11 × 10–15 m2, and the lowest value of horizontal hydraulic conductivity is 3.25 × 10–10 cm/s with intrinsic permeability equal to 3.32 × 10–19 m2. The kh/kv permeability ratio is generally >1.0, ranging from 0.02 to 19.9 and averaging 4.27.

At Site C0007 the highest value of vertical hydraulic conductivity is 1.24 × 10–9 cm/s with corresponding intrinsic permeability of 1.27 × 10–18 m2. The lowest value of vertical hydraulic conductivity is 9.54 × 10–10 cm/s with intrinsic permeability equal to 9.73 × 10–19 m2. The highest value of horizontal hydraulic conductivity is 1.15 × 10–9 cm/s with intrinsic permeability equal to 1.17 × 10–18 m2, and the lowest value of horizontal hydraulic conductivity is 8.09 × 10–10 cm/s with intrinsic permeability equal to 8.26 × 10–19 m2. The kh/kv ratio for Site C0007 ranges from 1.21 to 0.65 with a mean value 0.93.

Figure F7 shows how vertical and horizontal permeability values, together with the corresponding kh/kv ratio, change as the sampling depth increases. Values of vertical and horizontal permeability both decrease with increasing depth except for one anomalous sample that was taken from 300 m core depth below (CSF) (Sample 316-C0006E-39X-3, 48 cm). The anisotropy ratio for permeability shows a modest decrease with depth and an anomalous result at 150 m CSF (Sample 316-C0006E-22X-6, 5 cm).

Figure F8 displays the relation between permeability and porosity for tests conducted at an effective confining stress of 0.55 MPa. Porosity values were calculated from the post-test water content measurements (Table T1). The data do not show a systematic trend in the relation between porosity and permeability. In fact, for samples with porosity values between 35% and 45%, values of intrinsic permeability change by four orders of magnitude. There is an apparent segregation of values between the two sites. We note a shift toward higher porosities and lower permeabilities at Site C0007, although the number of samples tested is not large enough to demonstrate a definitive statistical difference.

Figure F9 shows all of the specimen images that were taken by ESEM. Figure F10 shows rose diagrams of particle orientation and corresponding values for the standard deviation and index of orientation. These values are also tabulated in Table T4. The standard deviation for grain orientation ranges from 30.5° to 56.5°, and the index of orientation ranges from 0.18 to 0.58. Figure F11 shows all corresponding cumulative frequency curves for particle orientation. With one exception, the standard deviations of orientation and the indexes of orientation are consistent with highly random arrangements of particles. Indexes of orientation are typically greater for the vertical section (parallel to core axis) than for the horizontal section (perpendicular to core axis). No clearly defined relation is apparent between the average indexes of orientation and depth of burial. Interpretation of these results, however, needs to take the dip of bedding into account, and for many samples the beds dip at angles >30° (Fig. F2; Table T2). For example, even if beds of mudstone display a strong bedding-parallel fabric (e.g., shale fissility) but dip close to 45°, we would not expect to see significant differences between the SEM images for horizontal and vertical sections.

Figure F12A illustrates the relation between permeability anisotropy and the microfabric orientation index for the horizontal section. Figure F12B shows how the anisotropy of permeability changes as a function of the orientation index ratio. Ratios of ih/iv range from ~0.5 to 1.3. For the majority of specimens, microfabric on the vertical cut face shows better preferred orientation than microfabric on the horizontal cut (ih < iv). Samples with significant increases in the anisotropy of permeability (kh/kv > 1) also show significant improvements of preferred orientation on the vertical cut face. This sensitivity of permeability to changes in grain fabric is to be expected as a weak fissility begins to develop with progressive compaction of the mudstone.