The influence of the cataclastic matrix on the petrophysical properties of deformation bands in arkosic sandstones (original) (raw)
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AAPG Bulletin, 2009
A series of deformation bands from various reservoir sandstones deformed at different burial depths have been studied with respect to microstructural and petrophysical variations. In many of the examples explored, the internal microstructure, porosity, and permeability vary along the bands at the centimeter or even millimeter scale, changing and in most cases reducing the ability of the bands to act as barriers to fluid flow. Porosity varies by up to 18% and permeability by up to two orders of magnitude. Such petrophysical variations are found along different types of deformation bands, but the range depends upon the deformation mechanisms, in particular on the degree of cataclasis and dissolution in cataclastic and dissolution bands, and on the phyllosilicate content in disaggregation bands. For cataclastic bands, the grain-size distribution changes along the bands with regard to the degree of cataclasis. Furthermore, the increased specific surface area of the pore-grain interface as a result of cataclasis causes higher permeability reduction in cataclastic bands than in other types of deformation bands. Phyllosilicate content can influence the thickness of phyllosilicate bands. However, no apparent correlation between thickness and intensity of cataclasis in the studied cataclastic deformation bands is observed.
Materiales de Construcción, 2007
Las areniscas miocenas estudiadas han sido y son ampliamente utilizadas en patrimonio histórico y en obra civil moderna, localizándose las canteras actuales en el borde de la depresión del Ebro. Se ha realizado un exhaustivo estudio de las características petrofísicas de estos materiales, que pese a presentar la misma edad y pertenecer a la misma cuenca sedimentaria presentan características mineralógicas y texturales diferentes que les confieren diferentes propiedades físicas, mecánicas y una diferente durabilidad. Las características petrográficas y petrofísicas se han evaluado mediante la realización de ensayos según las normas UNE, NORMAL y ASTM. Para todos los ensayos se ha realizado un tratamiento estadístico de los resultados para evaluar las posibles inhomogeneidades texturales y composicionales presentes en el material y que pueden originar modificaciones en su comportamiento. Los resultados ponen de manifiesto que estas areniscas presentan un importante valor industrial como materiales de usos constructivos, siendo la arenisca de Alcañiz la que presenta una mayor durabilidad como consecuencia de la configuración de su sistema poroso. Palabras clave: arenisca, propiedades físicas, durabilidad, petrofísica, piedra de construcción. Miocene sandstones studied were used extensively to build Aragon's architectural heritage, are still used in modern construction. The quarries presently located on the edge of the Ebro Valley depression. The present paper describes an exhaustive petrophysical study of these materials, which while, of the same age and from the same deposition basin, exhibit different mineralogical and textural characteristics and as a result, different physical and mechanical properties and durability. The petrographic and petrophysical characteristics of these materials were evaluated with tests prescribed in UNE (Spanish), NORMAL and ASTM standards. All the results were subjected to statistical analysis to identify possible textural and compositional nonuniformities in the material that may underlie behavioural changes. The results of the present paper show that their petrophysical characteristics afford these sandstones substantial industrial value as construction materials. Durability was found to be longest in the Alcañiz stone, as a result of the geometry of its pore network.
Deformation bands in sandstone: a review
Journal of the Geological Society, 2007
Deformation bands are the most common strain localization feature found in deformed porous 10 sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected 11 sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones 12 where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, 13 and/or compaction. Deformation bands with a component of shear are most common and typically 14 accommodate shear offsets of millimetres to centimetres. They can occur as single structures or cluster zones, 15 and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, 16 mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation 17 band formed. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show 18 the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. 19 Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show little influence 20 on fluid flow unless assisted by chemical compaction or cementation.
Geological Society, London, Special Publications, 2016
Deformation bands significantly alter the local petrophysical properties of sandstone reservoirs, although it is not known how the intrinsically variable characteristics of sandstones (e.g. grain size, sorting and mineralogy) influence the nature and distribution of deformation bands. To address this, cataclastic deformation bands within fine- and coarse-grained Triassic Sherwood Sandstone at Thurstaston, UK were analysed, for the first time, using a suite of petrographical techniques, outcrop studies, helium porosimetry and image analysis. Deformation bands are more abundant in the coarse-grained sandstone than in the underlying fine-grained sandstone. North- and south-dipping conjugate sets of cataclastic bands in the coarse-grained sandstone broadly increase in density (defined by number/m2) when approaching faults. Microstructural analysis revealed that primary grain size controls deformation band density. Deformation bands in both coarse and fine sandstones led to significantly...