The permeability of illite-rich shale from the Wilcox formation has been measured as a function of effective pressure for bedding-parallel flow of 1 M NaCl pore fluid. Permeability k decreases from ∼300×10−21 m2 to 3×10−21 m2 as effective pressure Pe is increased from 3 to 12 MPa; these values confirm that shales form effective barriers to fluid transport in sedimentary strata over extended geologic times. The variation of k with Pe for Wilcox shale is given by k = k0 [1 − (Pe/P1)m]3, where P1 = 19.3 (±1.6) MPa and m = 0.159 (±0.007). The value of k0 for Wilcox shale is of the order of 10−17 m2 and may vary among samples by as much as 70%. Effective pressure is given in terms of the external confining pressure Pc and internal pore pressure Pp by Pe = Pc − χPp, where χ = 0.99 (±0.06). While our measurements yield χ = ∼1 for shale with a clay content of ∼45%, others have reported χ values for clay-bearing sandstones that rise from ∼0.75 to 7.1 with increasing clay content (from 0 to 20%). The trends between χ and clay content revealed by these comparisons imply that the value of χ depends upon the relative distributions of compliant clay minerals and other stiffer minerals. These values of χ also suggest that effective pressures within interbedded sandstones and shales may differ, even at the same equilibrium Pc and Pp conditions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JB000273

Permeability of Wilcox shale and its effective pressure law

direction relative to bedding, clay content (40–65%), and effective pressure Pe (2– 12 MPa). Permeability k is anisotropic at low Pe; measured k values for flow parallel to bedding at Pe = 3 MPa exceed those for flow perpendicular to bedding by a factor of 10, both for low clay content (LC) and high clay content (HC) samples. With increasing Pe, k becomes increasingly isotropic, showing little directional dependence at 10–12 MPa. Permeability depends on clay content; k measured for LC samples exceed those of HC samples by a factor of 5. Permeability decreases irreversibly with the application of Pe, following a cubic law of the form k = k0 [1 � (Pe/P1) m ] 3 , where k0 varies over 3 orders of magnitude, depending on orientation and clay content, m is dependent only on orientation (equal to 0.166 for bedding-parallel flow and 0.52 for flow across bedding), and P1 (18–27 MPa) appears to be similar for all orientations and clay contents. Anisotropy and reductions in permeability with Pe are attributed to the presence of crack-like voids parallel to bedding and their closure upon loading, respectively. INDEX TERMS: 5114 Physical Properties of Rocks: Permeability and porosity; 5139 Physical Properties of Rocks: Transport properties; 5112 Physical Properties of Rocks: Microstructure; 1832 Hydrology: Groundwater transport; KEYWORDS: permeability, shale, connected pore space

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004JB003052

Permeability of illite-bearing shale: 1. Anisotropy and effects of clay content and loading

TEM study of in situ organic matter on continental margins: occurrence and the “monolayer” hypothesis

Compaction trends of clay-rich deep sea sediments

Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m2 on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to 15 km from the crest in the back arc direction. Combined with previous measurements, we find that the magnitude and spatial pattern of heat flow are similar to those at continental arcs. The heat flow in the Grenada basin to the west of the active arc is 0.06 W/m2, a factor of 2 lower than that found in the previous and most recent study. There is no thermal evidence for significant shallow fluid advection at any of these sites. Present-day volcanism is confined to the region with the highest heat flow.

/pdf/heat-flow-in-the-lesser-antilles-island-arc-and-adjacent-3were46y5y.pdf

Heat flow in the Lesser Antilles island arc and adjacent back arc Grenada basin

Porometry and fabric of marine clay and carbonate sediments: Determinants of permeability

In situ porosity and permeability were measured on Great Bahama Bank sediments using electrical conductivity and permeability probes. Core samples were recovered at the probe measurement sites for laboratory determinations of porosity and permeability. Penetration depths of cores and probes were approximately 2.5 m subbottom. In situ porosities of the oolitic sands for depths of 0–2.5 m subbottom ranged between 36% and 50%, and at sites in the somewhat muddier oolitic sediments the porosities ranged from 42% to 61%. The in situ permeabilities ranged from 0.0032 cm/s (3.3 darcys) to 0.068 cm/s (71 darcys) at the sites where porosities were determined. Laboratory values of porosity are comparable to values obtained by in situ measurements; however, laboratory permeability values are approximately an order of magnitude lower than in situ values. The reduced permeability measured in the laboratory is attributed to disturbance of the microfabric during coring, transport, and laboratory sampling. A det...

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 1: Measurements

Selected oolitic sediments from the Great Bahama Bank were studied to assess (1) the role of microfabric in determining porosity and permeability, and (2) particle packing relationships, i. e., grain support versus matrix support. Scanning electron microscopy and light microscopy revealed that the sediment consists of ooids, which are the major constituents of the sand‐size fraction, supported by a matrix composed predominantly of aragonite needles. The supporting matrix of aragonite needle clusters, which constitutes only about 10–20% of the total sediment dry weight, is the microstructural characteristic that increases the porosity and lowers the wet bulk density compared to a grain‐supported microfabric characteristic of clean sands. The presence of a fine‐grained matrix reduces the permeability of these sediments relative to clean sands. The influence of the microfabric is clearly reflected in the mass physical and depositional (particle packing) properties of the sediment. Laboratory values ...

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 2: Microfabric

We analyzed geotechnical and acoustic properties of sediments from Lau Basin backarc Sites 834, 835,838, and 839 to examine the large-scale heat and fluid circulation in the Lau Basin. We hypothesize that a feedback system exists in which sediment properties, particularly permeability, affect large-scale heat and fluid circulation and are, in turn, affected by the circulation of fluids. Sediments in the Lau backarc basin display none of the expected trends in physical and acoustic properties as a function of depth and are probably underconsolidated. The sediments can consolidate normally, however, as shown by measuring both compressional- and shear-wave velocity in a controlled laboratory triaxial setting. In-situ underconsolidation might occur because high sedimentation rates could prevent the sediments from dewatering and consolidating normally, or water lost during the consolidation process could be rapidly replaced by fluids circulating through the system convectively. Although initial sedimentation rates were extremely high in the Lau Basin, laboratory measurements indicate that the overlying clayey nannofossil oozes are sufficiently permeable to allow the passage of fluids through the sediments on the scale of several years; however, a comparison of vertical and horizontal components of flow indicates that horizontal fluid flow is 3 orders of magnitude greater than vertical flow. The highly permeable vitric silts and sands probably dominate the horizontal component of fluid flow. Measured vertical heat flow at these sites is much lower than would be predicted by a simple cooling model, suggesting that heat is flowing laterally. A large difference in measured heat flow exists between the lowermost stratigraphic units of Sites 834 and 835, indicating that lateral fluid flow may be occurring. The chemistry of pore fluids measured at Sites 834, 835, and 838 shows an increase and subsequent decrease in dissolved calcium with depth within the sediment column, again suggesting lateral fluid flow. The dissolved-calcium profile at Site 839 shows a seawater signature and no consistent trend downhole, indicating possible downwelling of bottom water throughout the entire sediment column. The volume of fluid required to (1) dissipate the excess heat expected but not measured and (2) prevent the sediments from consolidating normally in these Lau backarc sites is very small, about 8 m3 at Site 834. Very small gradients are required to replace this amount of fluid lost during the 5.5 m.y. of sediment deposition. In general, sites of downwelling are much more diffuse and cooler than sites of upwelling. Site 839 probably is a downwelling site. The remaining three sites possibly are located in a zone of lateral fluid flow within a large-scale, convective circulation cell.

http://www-odp.tamu.edu/publications/135_SR/VOLUME/CHAPTERS/sr135_48.pdf

48. geotechnical and logging evidence for underconsolidation of lau basin sediments: rapid sedimentation vs. fluid flow1

Distribution of pore space and degree of cementation appear to be the main factors controlling the permeability of sediments retrieved from the Lau Basin. The undisturbed microfabrics of two lithologies, nannofossil ooze and vitric sandy silt, commonly found at Holes 834A, 835A, 838A, and 839Aof Leg 135 were examined by scanning electron microscopy equipped with energy dispersive X-ray spectral analysis and image analysis systems. The results of these analyses were compared with laboratory determinations of porosity, grain-size distribution, and permeability on discrete samples from the same sediment depths. The permeability of the vitric sandy silt is 3-5 orders of magnitude higher than the nannofossil ooze samples. The porosity of nannofossil ooze ranges from 6% to 12% greater than the porosity of vitric sandy silt, which partially reflects the finer texture of nannofossil ooze. Although the correlation of higher porosity with lower permeability is not surprising, factors other than simply grain-size distribution must be invoked to explain the large differences in permeability found in these samples.

http://www-odp.tamu.edu/publications/135_SR/VOLUME/CHAPTERS/sr135_49.pdf

Kathleen M. Fischer

Papers

Porometry and fabric of marine clay and carbonate sediments: Determinants of permeability

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 1: Measurements

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 2: Microfabric

48. geotechnical and logging evidence for underconsolidation of lau basin sediments: rapid sedimentation vs. fluid flow1

49. geotechnical properties of lau basin sediments from a microfabric perspective1