Mechanical compaction and strain localization in Bleurswiller sandstone

Baud, Patrick; Reuschlé, Thierry; Ji, Yuntao; Cheung, C. S. N.; Wong, Teng-fong

doi:10.1002/2015jb012192

Cited by 69 publications

(57 citation statements)

References 40 publications

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“…Figures show the numerical scheme verification and results of deformation processes on this sandstone for both brittle and ductile behaviors. Simulation results of shear damage and grain crushing that lead to the formation of localized bands show to be consistent with experimental observations . Depending on the confining pressure level, the rock exhibits shear or compaction localized bands.…”

Section: Computational Results and Discussionsupporting

confidence: 81%

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

Garavand

Stefanov

Rebetsky

et al. 2020

Num Anal Meth Geomechanics

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Summary In many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear‐induced dilation and shear‐enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near‐wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed‐mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog‐eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear‐enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress.

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Section: Computational Results and Discussionsupporting

confidence: 81%

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

Garavand

Stefanov

Rebetsky

et al. 2020

Num Anal Meth Geomechanics

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show abstract

“…a layer of reduced porosity). This is supported by the results from a recent study by Baud et al (2015), which examined compaction bandbearing sandstones using X-ray-computed tomography. The authors show that when compaction bands are formed in a rock with porosity clusters, their path is more tortuous than in material with homogeneous porosity; consequently, the bands do not comprise efficient permeability barriers in three dimensions.…”

Section: Microstructural Controls On Permeability Evolutionsupporting

confidence: 74%

Inelastic compaction and permeability evolution in volcanic rock

2017

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Abstract. Active volcanoes are mechanically dynamic environments, and edifice-forming material may often be subjected to significant amounts of stress and strain. It is understood that porous volcanic rock can compact inelastically under a wide range of in situ conditions. In this contribution, we explore the evolution of porosity and permeability -critical properties influencing the style and magnitude of volcanic activity -as a function of inelastic compaction of porous andesite under triaxial conditions. Progressive axial strain accumulation is associated with progressive porosity loss. The efficiency of compaction was found to be related to the effective confining pressure under which deformation occurred: at higher effective pressure, more porosity was lost for any given amount of axial strain. Permeability evolution is more complex, with small amounts of stress-induced compaction ( < 0.05, i.e. less than 5 % reduction in sample length) yielding an increase in permeability under all effective pressures tested, occasionally by almost 1 order of magnitude. This phenomenon is considered here to be the result of improved connectivity of formerly isolated porosity during triaxial loading. This effect is then overshadowed by a decrease in permeability with further inelastic strain accumulation, especially notable at high axial strains (> 0.20) where samples may undergo a reduction in permeability by 2 orders of magnitude relative to their initial values. A physical limit to compaction is discussed, which we suggest is echoed in a limit to the potential for permeability reduction in compacting volcanic rock. Compiled literature data illustrate that at high axial strain (both in the brittle and ductile regimes), porosity φ and permeability k tend to converge towards intermediate values (i.e. 0.10 ≤ φ ≤ 0.20; 10 −14 ≤ k ≤10 −13 m 2 ). These results are discussed in light of their potential ramifications for impacting edifice outgassing -and in turn, eruptive activity -in active volcanoes.

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“…During all the experiments, p c and p p were kept constant by compensating for deviations by using servo‐controlled pressure intensifiers. The recorded movement of the p p intensifier yields the change in pore volume during nonhydrostatic deformation and unloading of the sample, which we normalize to give the porosity change δϕ , related to the volumetric strain undergone by a sample [ Baud et al ., ]. We show this differential as positive during dilation and negative during compaction.…”

Section: Methodsmentioning

confidence: 73%

Strain‐induced permeability increase in volcanic rock

Farquharson

Heap

Baud

2016

Geophysical Research Letters

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The extrusion of dense, viscous magma typically occurs along pronounced conduit‐parallel faults. To better understand the evolution of fault permeability with increasing strain, we measured the permeability of low‐porosity volcanic rock samples (basalt and andesite) that were deformed in the brittle regime to various levels of inelastic strain. We observed a progressive increase in sample permeability with increasing inelastic strain (i.e., with continued sliding on the fault plane). At the maximum imposed inelastic strain (0.11), sample permeability had increased by 3 orders of magnitude or more for all sample sets. Microstructural observations show that narrow shear fractures evolve into more complex fracture systems characterized by thick zones of friction‐induced cataclasis (gouge) with increasing inelastic strain. These data suggest that the permeability of conduit‐parallel faults hosted in the rock at the conduit‐wall rock interface will increase during lava extrusion, thus facilitating outgassing and hindering the transition to explosive behavior.

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Mechanical compaction and strain localization in Bleurswiller sandstone

Cited by 69 publications

References 40 publications

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

Inelastic compaction and permeability evolution in volcanic rock

Strain‐induced permeability increase in volcanic rock

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