Previous   |    Next

doi:10.2204/iodp.proc.322.211.2015

Results

Table T1 summarizes values of water content and porosity for trimmings measured before and after each flow-through test. In some cases, water content decreased relative to shipboard values, and those discrepancies probably were caused by escape of moisture during shipment and storage of the WR specimens. For two specimens (322-C0012A-8R-3 and 333-C0011D-49X-5), values of porosity increased after the flow-through test. That perturbation was probably caused by expansion of water-filled microcracks after the confining pressure of 0.55 MPa was released. Each individual test result is illustrated in the “Appendix.” Table T2 shows values of volumetric flow rate, discharge velocity, steady-state head loss, steady-state hydraulic gradient, hydraulic conductivity, and intrinsic permeability for each test. Table T4 summarizes the average values of permeability for each horizontal and vertical specimen and the corresponding k_h/k_v ratio.

As also noted by Dugan and Zhao (2013), drilling and coring disturbance was both extensive and severe during Expedition 322. Consequently, permeability values for those cores should be interpreted with caution, essentially serving as upper limits on in situ permeability. At Site C0011 (flank of Kashinosaki Knoll), the highest value of vertical hydraulic conductivity (K_v) is 1.31 × 10^–8 cm/s, with k = 1.31 × 10^–17 m². The lowest value of K_v is 3.70 × 10^–10 cm/s, with k_v = 3.67 × 10^–19 m². The highest value of horizontal hydraulic conductivity (K_h) is 1.76 × 10^–8 cm/s, with k_h = 1.75 × 10^–17 m². The lowest value of K_h is 5.06 × 10^–10 cm/s, with k_h = 5.02 × 10^–19. The ratio k_h/k_v is generally close to 1.0, ranging from 0.87 to 1.78 and averaging 1.26. Sample 322-C0011B-3R-4 yielded unusually inconsistent results for the four replicate tests (Table T2); its average permeability value is significantly greater than averages for nearby Sample 333-C0011D-49X-5 (Table T4), and that scatter may also be a symptom of coring damage.

At Site C0012 (crest of Kashinosaki Knoll), the highest value of K_v is 3.25 × 10^–8 cm/s, with a corresponding k_v of 3.23 × 10^–17 m². The lowest value of vertical K_v is 1.69 × 10^–9 cm/s, with k_v = 1.68 × 10^–18 m². The highest value of K_h is 1.76 × 10^–8 cm/s, with k_h = 1.75 × 10^–17 m². The lowest value of K_h is 5.06 × 10^–10 cm/s, with k_h = 5.02 × 10^–19 m². The k_h/k_v ratio is generally close to 1.0, ranging from 0.87 to 2.82 and averaging 1.57. The largest amount of anisotropy occurs in a sample from an interval of slumping, where bedding dips are ~60°.

Figure F7 illustrates how values of vertical and horizontal permeability change with depth of burial. The range of values is consistent with the test results of Dugan and Zhao (2013) and Screaton et al. (2013) over comparable depth intervals. For the most part, values of both vertical and horizontal permeability decrease with depth, but the anisotropy of permeability remains close to 1. Figure F8 displays the relation between permeability and porosity at an effective confining stress of 0.55 MPa. As expected, the test results show a systematic decrease in permeability as porosity decreases.

Figure F9 catalogs the rose diagrams of particle orientation and corresponding values for the standard deviation, index of orientation, mean angle, and resultant vector length (see Table T3 for microfabric statistics). The cumulative frequency curves are plotted on Figure F10. The standard deviation for grain orientation ranges from 48.6° to 62.5°, and the index of orientation ranges from 0.14 to 0.33. The mean angle ranges from 8.77° to 178.11°, and the resultant vector length ranges from 0.055 to 0.220. All such values are consistent with random arrangements of particles. Ratios of i_h/i_v range from ~0.87 to 2.82. For the majority of specimens, microfabric on the vertical cut face shows better preferred orientation than microfabric on the horizontal cut (i.e., i_h < i_v). No trend is apparent between the indexes of orientation and depth of burial (Fig. F11). Similarly, we see no meaningful trend in k_h/k_v vs. depth (Fig. F11). Linear regression shows that the relation between permeability anisotropy and i values is not statistically significant. Samples with higher anisotropy of permeability (k_h/k_v > 1) tend to display better grain alignment on the vertical cut face, but the correlation coefficient is only 0.167 for the regression between k_h/k_v and i_h/i_v. We surmise that enhanced grain alignment probably affects permeability more as compaction progresses below the range of our sampling.

Top of page   |    Previous   |    Next