Effects of pore collapse and grain crushing on ultrasonic velocities andVp/Vs

Abstract. We analyse deformation bands related to horizontal contraction with an intermittent period of horizontal extension in Miocene turbidites of the Whakataki Formation south of Castlepoint, Wairarapa, North Island, New Zealand. In the Whakataki Formation, three sets of cataclastic deformation bands are identified: (1) normal-sense compactional shear bands (CSBs), (2) reverse-sense CSBs, and (3) reverse-sense shear-enhanced compaction bands (SECBs). During extension, CSBs are associated with normal faults. When propagating through clay-rich interbeds, extensional bands are characterised by clay smear and grain size reduction. During contraction, sandstone-dominated sequences host SECBs, and rare CSBs, that are generally distributed in pervasive patterns. A quantitative spacing analysis shows that most outcrops are characterised by mixed spatial distributions of deformation bands, interpreted as a consequence of overprint due to progressive deformation or distinct multiple generations of deformation bands from different deformation phases. As many deformation bands are parallel to adjacent juvenile normal faults and reverse faults, bands are likely precursors to faults. With progressive deformation, the linkage of distributed deformation bands across sedimentary beds occurs to form through-going faults. During this process, bands associated with the wall-, tip-, and interaction-damage zones overprint earlier distributions resulting in complex spatial patterns. Regularly spaced bands are pervasively distributed when far away from faults. Microstructural analysis shows that all deformation bands form by inelastic pore collapse and grain crushing with an absolute reduction in porosity relative to the host rock between 5 % and 14 %. Hence, deformation bands likely act as fluid flow barriers. Faults and their associated damage zones exhibit a spacing of 9 m on the scale of 10 km and are more commonly observed in areas characterised by higher mudstone-to-sandstone ratios. As a result, extensive clay smear is common in these faults, enhancing the sealing capacity of faults. Therefore, the formation of deformation bands and faults leads to progressive flow compartmentalisation from the scale of 9 m down to about 10 cm – the typical spacing of distributed, regularly spaced deformation bands.

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Effect of Pore Collapse and Grain Crushing on the Frequency Dependence of Elastic Wave Velocities in a Porous Sandstone

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-020-02213-0 ◽

2020 ◽

Vol 53 (11) ◽

pp. 5081-5093

Author(s):

Chao Sun ◽

Jan V. M. Borgomano ◽

Jérôme Fortin ◽

ShangXu Wang

Keyword(s):

Elastic Wave ◽

Frequency Dependence ◽

Pore Collapse ◽

Wave Velocities ◽

Grain Crushing ◽

Porous Sandstone

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Grain Crushing, Pore Collapse and Strain Localization in Porous Sandstone

Mechanics of Natural Solids ◽

10.1007/978-3-642-03578-4_11 ◽

2009 ◽

pp. 239-254 ◽

Cited By ~ 1

Author(s):

Teng-fong Wong ◽

Patrick Baud

Keyword(s):

Strain Localization ◽

Pore Collapse ◽

Grain Crushing ◽

Porous Sandstone

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Effect of Loading Path and Porosity on the Failure Mode of Porous Rocks

Applied Mechanics Reviews ◽

10.1115/1.3119759 ◽

1992 ◽

Vol 45 (8) ◽

pp. 281-293 ◽

Cited By ~ 74

Author(s):

Teng-fong Wong ◽

Hiram Szeto ◽

Jiaxiang Zhang

Keyword(s):

Acoustic Emission ◽

Strain Hardening ◽

Yield Locus ◽

Loading Path ◽

High Porosity ◽

Porous Rocks ◽

Stress Space ◽

Pore Collapse ◽

Clastic Rocks ◽

Grain Crushing

Grain crushing and pore collapse are the dominant compaction mechanisms in high porosity clastic rocks. These micromechanical processes control the evolution of strain hardening during cataclastic flow, and they can also result in embrittlement of the rock. The mechanics of the transition from brittle fracture to homogeneous cataclastic flow for the Berea and Kayenta sandstones were investigated in the laboratory. The mechanical data show that the transition is sensitively dependent on the stress state as well as the porosity. In the stress space, the complete locus for brittle failure by shear localization can be determined by tests on normally consolidated and overconsolidated samples along different loading paths. Using porosity as the hardening parameter, the evolution of the inelastic yield locus with strain hardening can be mapped out in the stress space. This yield locus expands with decreasing porosity. Scanning electron microscope and acoustic emission measurements were used to elucidate the micromechanics. The onset of grain crushing and pore collapse was marked by a surge in acoustic emission activity. A Hertzian fracture mechanics model was formulated to analyze the roles of porosity, grain size and fracture toughness in controlling the onset of hydrostatic and shear-enhanced compaction. Stereological measurements of the microcrack density show that significant stress-induced anisotropy was induced by shear-enhanced compaction, with preferred orientations of the stress-induced microcracks subparallel to the maximum compression direction.

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Distribution, microphysical properties, and tectonic control of deformation bands in the Miocene accretionary prism (Whakataki Formation) of the Hikurangi subduction zone

10.5194/se-2020-80 ◽

2020 ◽

Author(s):

Kathryn E. Elphick ◽

Craig R. Sloss ◽

Klaus Regenauer-Lieb ◽

Christoph E. Schrank

Keyword(s):

Microstructural Analysis ◽

Shear Bands ◽

Accretionary Prism ◽

Normal Faults ◽

Pore Collapse ◽

Deformation Bands ◽

Progressive Deformation ◽

Compaction Bands ◽

Grain Crushing ◽

Normal Sense

Abstract. We analyse deformation bands related to both horizontal contraction and horizontal extension in Miocene turbidites of the Whakataki Formation south of Castlepoint, Wairarapa, North Island, New Zealand. In the Whakataki Formation, four sets of cataclastic deformation bands are identified: (1) normal-sense Compactional Shear Bands (CSBs); (2) normal-sense Shear-Enhanced Compaction Bands (SECBs); (3) reverse-sense CSBs; and (4) reverse-sense SECBs. During extension, CSBs form most frequently with rare SECBs. Extensional CSBs are often, but not exclusively, associated with normal faults. During contraction, distributed SECBs are observed most commonly, sometimes clustering around small reverse faults and thrusts. Contractional CSBs are primarily found in the damage zones of reverse faults. The quantitative spacing analysis shows that most outcrops are characterised by mixed spatial distributions of deformation bands, interpreted as a consequence of overprint due to progressive deformation or distinct multiple generations of deformation bands from different deformation phases. Since many deformation bands are parallel to adjacent juvenile normal- and reverse-faults, bands are likely precursors to faults. With progressive deformation, the linkage of distributed deformation bands across sedimentary beds occurs to form through-going faults. During this process, bands associated with the wall-, tip-, and interaction damage zones overprint earlier distributions resulting in complex spatial patterns. Regularly spaced bands are pervasively distributed when far away from faults. Microstructural analysis shows that all deformation bands form by inelastic pore collapse and grain crushing with an absolute reduction in porosity relative to the host rock between 5 and 14 %. Hence, deformation bands likely act as fluid flow barriers. Faults and their associated damage zones exhibit a spacing of order ten metres on the scale of 10 km and are more commonly observed in areas characterised by higher mudstone to sandstone ratios. As a result, extensive clay smear is common in these faults, enhancing the sealing capacity of faults. Therefore, the formation of deformation bands and faults leads to progressive flow compartmentalisation from the scale of ten metres down to about ten centimetres, the typical spacing of distributed deformation bands.

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The effect of grain size and porosity on compaction localisation in high-porosity sandstones

10.5194/egusphere-egu21-11020 ◽

2021 ◽

Author(s):

Elliot Rice-Birchall ◽

Daniel Faulkner ◽

John Bedford

Keyword(s):

Grain Size ◽

Axial Strain ◽

Size Reduction ◽

High Porosity ◽

Pore Collapse ◽

Band Formation ◽

Compaction Bands ◽

Grain Crushing ◽

Porosity Reduction ◽

Compaction Band

<p>As sandstone reservoirs are depleted, the pore pressure reduction can sometimes result in pore collapse and the formation of compaction bands. These are localised features which can significantly reduce the bulk permeability of the reservoir and are therefore problematic in the oil, water, geothermal, and CO<sub>2</sub> sequestration industries. However, the influence that grain size, grain shape and sorting have on compaction band formation in sandstone is still poorly understood, due to the fact that finding natural sandstones with specific properties is challenging. Consequently, a method of forming synthetic sandstones has been developed, in order to produce a suite of sandstone specimens with controlled grain size and porosity characteristics. During production of the synthetic sandstones, amorphous quartz cement and sodium chloride are precipitated between sand grains as a product of the reaction between sodium silicate and hydrochloric acid. The salt can then be dissolved, resulting in synthetic sandstones that have very comparable physical properties to their natural counterparts. In this study, triaxial experiments were performed on synthetic sandstone cores with four different grain size ranges of 250-300, 425-500, 600-710 and 850-1000 microns, at three different starting porosities of 27%, 32% and 37%. The samples were each axially loaded from a point along their hydrostat corresponding to 85% of their hydrostatic yield point, P*, values. These conditions mean that failure will occur within the shear-enhanced compaction regime so as to try and produce localised compaction structures. All samples were taken to 5% axial strain. The microstructural results indicate that localisation of deformation within the samples did occur and was favoured in the low starting porosity, small grain size samples. Localisation of deformation was most easily recognised by grain size reduction through grain crushing. This was weakly correlated to a change in porosity but recognition of the localisation of deformation was difficult to make using variations in porosity alone. Porosity reduction was not necessarily associated with a reduction in grain size. With increasing grain size and starting porosity, the deformation becomes more distributed in the samples with the highest starting porosity samples (37%) exhibiting more widely distributed grain crushing which was less intense overall. The results indicate a significant grain size and starting porosity influence on localisation, but also that compaction can occur by two mechanisms; one involving mostly grain rearrangement and the other primarily by grain fracturing. Consequently, the localisation of deformation is most evident in grain size reduction and is only weakly shown by porosity reduction.</p>

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Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids

Materials ◽

10.3390/ma14112731 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2731

Author(s):

Ameya Rege

Keyword(s):

Constitutive Model ◽

Cell Walls ◽

Compressive Strain ◽

Pore Collapse ◽

Compressive Response ◽

Linear Elastic ◽

Nonlinear Springs ◽

Different Types ◽

Point Of Intersection ◽

Good Agreement

The macroscopic mechanical behavior of open-porous cellular materials is dictated by the geometric and material properties of their microscopic cell walls. The overall compressive response of such materials is divided into three regimes, namely, the linear elastic, plateau and densification. In this paper, a constitutive model is presented, which captures not only the linear elastic regime and the subsequent pore-collapse, but is also shown to be capable of capturing the hardening upon the densification of the network. Here, the network is considered to be made up of idealized square-shaped cells, whose cell walls undergo bending and buckling under compression. Depending on the choice of damage criterion, viz. elastic buckling or irreversible bending, the cell walls collapse. These collapsed cells are then assumed to behave as nonlinear springs, acting as a foundation to the elastic network of active open cells. To this end, the network is decomposed into an active network and a collapsed one. The compressive strain at the onset of densification is then shown to be quantified by the point of intersection of the two network stress-strain curves. A parameter sensitivity analysis is presented to demonstrate the range of different material characteristics that the model is capable of capturing. The proposed constitutive model is further validated against two different types of nanoporous materials and shows good agreement.

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Modelling of Pore Collapse during Polymer Sintering: Viscoelastic Model with Enclosed Gas

Materials ◽

10.3390/ma14092182 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2182

Author(s):

Florian Wohlgemuth ◽

Dirk Lellinger ◽

Ingo Alig

Keyword(s):

Surface Tension ◽

Gas Transport ◽

Selective Laser Sintering ◽

Viscoelastic Model ◽

Polymer Melt ◽

Gas Diffusion ◽

Gas Pressure ◽

Parameter Study ◽

Time Interval ◽

Pore Collapse

Frenkel’s model for the late stage of coalescence of viscous particles has been extended to describe pore collapse in a viscoelastic melt during polymer sintering. The shrinkage of a pore in a polymer melt driven by surface tension is extended by taking into account the effects of trapped gas and gas transport out of the pore. Viscoelasticity has been shown to have a considerable impact on the time scale of the coalescence process. In addition, gas diffusion modifies the coalescence dynamics. Based on a parameter study, different regimes for the pore collapse have been identified. At the beginning of pore collapse, surface tension is considerably stronger than gas pressure within the pore. In this time interval (surface-tension-driven regime), the pore shrinks even in the absence of gas diffusion through the matrix. In the absence of gas transport, the shrinkage dynamic slows down and stops when the surface tension balances the gas pressure in the pore. If gas transport out of the pore is possible, surface tension and gas pressure are balanced while the gas pressure slowly decreases (diffusion-controlled regime). The final phase of pore collapse, which occurs when the gas pressure within the pore decreases sufficiently, is controlled again by surface tension. The limitations of the model are discussed. To analyze the interplay between different mechanisms and process steps during selective laser sintering, the respective time scales are compared using experimental data.

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