Mechanical compaction of sand/clay mixtures

Abstract

[1] Compaction of siliciclastic sediments is of interest for the study of numerous transport processes occurring in sedimentary basins. Mechanical compaction of sand/ clay mixtures depends on the clay content, the effective stress history, and both the mechanical compaction coefficients and the depositional porosities of the two endmembers (clean sand and pure shale). The porosity/depth profiles of siliciclastic sediments result from the superposition of two kinds of spatial variations. The first component corresponds to compaction of the mixture with depth of burial. The second component corresponds to small-scale variations of the clay content during deposition and clay infiltration processes. The porosity/depth data are bounded by a minimum porosity/depth envelope corresponding to clay content at the limit between the shaly sand domain and the sandy shale domain. There are two possible upper bounds corresponding to small or large clay contents. The porosity of the clean sand endmember decreases with the depth of burial until a critical porosity of 0.25-0.40 is reached. This critical porosity corresponds to the porosity of random assemblages of more or less spherical grains and depends on the grain-size distribution of the sand grain assemblage. The critical porosity of the shale end-member is much smaller because of the high aspect ratio of the clay particles. The model developed here is applied to downhole measurements made in a borehole that penetrates 3 km of Mio-Pleistocene shaly sand series. The compaction model agrees well with the observed compaction profile.

Influence of surface conductivity on the apparent zeta potential of calcite

“…Equation (5) developed by Revil et al [14,15] is very close to the HS equation (Eq. (6)), except that the electrical conductivity of the bulk pore water w σ in the HS equation is replaced by the product of the electrical formation factor and electrical conductivity of the sample, Fσ, in Eq.…”

“…al. [14,15] for the streaming potential coupling coefficient when surface conductivity effects can be neglected. By combining Eqs.…”

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

“…It also closely approximates well documented porositydepth behaviour under normal compaction, at least within the upper 2-3 km of the crust where mechanical processes predominate (Athy 1930;Weller 1959;Magara 1978;Fowler & Yang 1998;Bahr et al 2001;Yang 2001;Revil et al 2002). Chemical compaction exerts significant influence at greater depth, initiating at temperatures of 70-100 • C, and it might lead to deviations from strictly exponential porosity-depth behaviour (Bjørlykke 1999).…”

How well can we predict permeability in sedimentary basins? Deriving and evaluating porosity–permeability equations for noncemented sand and clay mixtures

“…Revil & Cathles (1999) and Revil (2002) used a modified Kozeny-Carman equation to calculate the permeability of the sand fraction (k sd* ) and a power law equation similar to Eq. 3 to calculate the permeability of the clay fraction (k cl* ).…”