Shear Band Characterization of Triaxial Sand Specimens Using Computed Tomography

Suits, L David; Sheahan, TC; Batiste, SN; Alshibli, KA; Sture, Stein; Lankton, M. R.

doi:10.1520/gtj12080

Cited by 31 publications

(3 citation statements)

References 7 publications

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“…On a horizontal section through the damaged zone, we observe numerous dark spots (low density, probably large pores/discontinuities) as well as a pattern of bright radial linear structures (high-density zones) (Figure 14a). To our knowledge, such radial features have not been observed in triaxial loading experiments in consolidated rocks, but similar features were observed in [Batiste et al, 2004] (Figure 14b). Similar features have also been found experimentally by Desrues et al [1996] and were reproduced by Fazekas et al [2006] using distinct element method (DEM) numerical simulation on unconsolidated granular media.…”

Section: Strain Localization Patternssupporting

confidence: 80%

Mechanical instability induced by water weakening in laboratory fluid injection tests

David¹,

Dautriat

Sarout

et al. 2015

JGR Solid Earth

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To assess water‐weakening effects in reservoir rocks, previous experimental studies have focused on changes in the failure envelopes derived from mechanical tests conducted on rocks fully saturated either with water or with inert fluids. So far, little attention has been paid to the mechanical behavior during fluid injection under conditions similar to enhanced oil recovery operations. We studied the effect of fluid injection on the mechanical behavior of the weakly consolidated Sherwood sandstone in laboratory experiments. Our specimens were instrumented with 16 ultrasonic P wave transducers for both passive and active acoustic monitoring during loading and fluid injection to record the acoustic signature of fluid migration in the pore space and the development of damage. Calibration triaxial tests were conducted on three samples saturated with air, water, or oil. In a second series of experiments, water and inert oil were injected into samples critically loaded up to 80% or 70% of the dry or oil‐saturated compressive strength, respectively, to assess the impact of fluid migration on mechanical strength and elastic properties. The fluids were injected with a low back pressure to minimize effective stress variations during injection. Our observations show that creep takes place with a much higher strain rate for water injection compared to oil injection. The most remarkable difference is that water injection in both dry and oil‐saturated samples triggers mechanical instability (macroscopic failure) within half an hour whereas oil injection does not after several hours. The analysis of X‐ray computed tomography images of postmortem samples revealed that the mechanical instability was probably linked to loss of cohesion in the water‐invaded region.

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Section: Strain Localization Patternssupporting

confidence: 80%

Mechanical instability induced by water weakening in laboratory fluid injection tests

David¹,

Dautriat

Sarout

et al. 2015

JGR Solid Earth

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“…white arrows) which, in some cases, propagate toward the surfaces forming radial features. Such type of deformation with multiple radial fractures has been observed also by David et al (2015b) on Sherwood sandstone samples after injection tests, following the same experimental methodology, and by Batiste et al (2004) and Desrues et al (1996) on a sand pack deformed in triaxial experiments. The similarity between these observations lead David et al (2015b) to interpret such features as due to a loss of cohesion between the grains in the waterinvaded part.…”

Section: Microstructures Resulting From Injection Testssupporting

confidence: 65%

Water-Induced Damage in Microporous Carbonate Rock by Low-Pressure Injection Test

et al. 2021

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In the present work, we investigate the mechanical weakening and deformation induced by water on a microporous carbonate rock, the Obourg Chalk from Mons Basin (Belgium), through conventional triaxial tests and injection tests. The injection tests were conducted by waterflooding critically loaded rock samples, initially in dry condition, in a way to minimize the variations in the effective pressures. Furthermore, the samples were instrumented with P-wave piezoelectric transducers to provide active ultrasonic monitoring while injecting. The results show a significant reduction in the mechanical strength of this chalk. Analysis of the mechanical tests and the associated deformation allows us to describe the mechanical behavior as a function of the confining pressure, which draws a brittle-ductile transition spanning from low to high confining pressure. The injection tests, moreover, revealed that the amount of water injected before triggering mechanical instability decreases exponentially with respect to the applied differential stress on the rock sample. The data, therefore, suggest that the failure might be controlled by a mechanical coupling between the water-invaded zone and the dry one. Since water-weakening plays an important role in several fields like oil industry, through secondary and tertiary recovery of hydrocarbons, Enhanced Geothermal Systems (EGS), as well as in the mechanical stability of underground cavities, the outcome of this work is of primary importance in mitigating any kind of problems related to these operations.

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“…At axial strain, a = 25%, q/p was 1.25 for the loose specimens of Ottawa sand and Siligran and 1.4 for Q-Rok. All specimens continued to dilate even at large strains possibly due to formation of new shearing bands as seen in 3D computed tomography images [68][69][70]. Dilation was considerably greater for the dense specimens than for the loose specimens.…”

Section: Triaxial Testsmentioning

confidence: 92%

Effect of Particle Morphology on Stiffness, Strength and Volumetric Behavior of Rounded and Angular Natural Sand

Sharma¹,

Leib-Day²,

Thakur

et al. 2021

Materials

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Stress–strain and volume change behavior for clean sands which have distinct particle shape (rounded and angular) with very similar chemical (mineralogical) composition, size, and texture in one-dimensional (1D) compression and drained triaxial compression are presented. The effect of particle morphology on the crushing behavior in one-dimensional loading is explored using laser light diffraction technique which is suitable for particle crushing because of its high resolution and small specimen volume capability. Particle size distribution in both volume/mass and number distributions are considered for improved understanding associated with the process of comminution. Number distributions present a clearer picture of particle crushing. It is argued that particle crushing in granular assemblies initiates in larger particles, rather than in smaller particle. It was found that rounded sand specimens showed greater crushing than angular sand specimens with higher uniformity coefficient. In 1D compression, loose specimens compress approximately 10% more than dense specimens irrespective of particle shape. Densification of angular sand results in improvement in stiffness (approximately 40%) and is comparable to that of loose rounded sand. In general, density has a greater influence on the behavior of granular materials than particle morphology. The effect of particle shape was found to be greater in loose specimens than in dense specimens. The effect of grain shape on critical state friction angle is also quantified.

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Shear Band Characterization of Triaxial Sand Specimens Using Computed Tomography

Cited by 31 publications

References 7 publications

Mechanical instability induced by water weakening in laboratory fluid injection tests

Mechanical instability induced by water weakening in laboratory fluid injection tests

Water-Induced Damage in Microporous Carbonate Rock by Low-Pressure Injection Test

Effect of Particle Morphology on Stiffness, Strength and Volumetric Behavior of Rounded and Angular Natural Sand

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