Sand Textural Control on Shear-Enhanced Compaction Band Development in Poorly-Lithified Sandstone

Abstract

Sand textural control on SECB (shear-enhanced compaction band) formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Provence (France). Field observations show that SECBs are densely distributed in a coarse-grained unit with moderate porosity (27%), whereas few SECBs are developed within the overlying fine-grained, high-porosity (39%) unit. Results from textural characterization show that the main difference between the two sand units is grain size and sorting, whereas they are similar with respect to composition and grain angularity. Packing density is introduced as an important parameter for comparing the compaction properties independent of the textural variations between the two units. Compaction experiments show a slightly faster compaction of the coarse-grained sand as compared to the fine-grained sand, and more pronounced grain crushing is observed in the coarse-grained unit. The results indicate that the preferential localization of SECBs to the coarse-grained unit is controlled by a slightly denser packing of the coarse-grained material at the time of band formation together with higher stress concentrations on grain contacts. Hence, this study emphasizes that porosity alone is an insufficient parameter for predicting deformation band evolution in sand (stone).

Deformation ‘boundary front’ movements in subglacial tills—A microsedimentological perspective from till sequences near Pine Point, NWT, Canada

“…It seems probable, given the rheology of these tills with relatively high clay contents, that the grain stacks pre‐dated the microshears and may indicate extension and boudinage within the till (Goscombe, Passchier, & Hand, ; Passchier & Trouw, ). In discussions on the evolution of microstructures in sediments it has been shown that there is a set of microstructure development types that passes from grain stacks to edge‐to‐edge grain crushing, to microshears and finally deformation bands (Fossen et al, ; Haines et al, ; Haines, Marone, & Saffer, ; Hiemstra & van der Meer, ; Menzies et al, ; Skurtveit et al, ; Figure ).…”

Assessing continuum plasticity postulates with grain stress and local strain measurements in triaxially compressed sand

“…There is significant evidence that unconsolidated sands and sediments and poorly lithified sandstones undergo shear banding, accompanied by either dilation at low pressures or compaction at high pressures, throughout the Earth’s upper crust ( 16 – 19 ). The mechanical behavior of these materials, and specifically their propensity to develop shear and deformation bands, is of significant importance because of their application as reservoirs for hydrocarbon extraction and CO 2 storage ( 20 ).…”

“…The mechanical behavior of these materials, and specifically their propensity to develop shear and deformation bands, is of significant importance because of their application as reservoirs for hydrocarbon extraction and CO 2 storage ( 20 ). These materials have therefore been tested under conditions similar to those found in their reservoir applications (5 to 50 MPa) ( 13 , 19 – 22 ), and their mechanical behaviors have been interpreted using critical state plasticity theories ( 16 – 18 ).…”