Static and dynamic stiffness measurements with Opalinus Clay

Lozovyi, Serhii; Bauer, Andreas

doi:10.1111/1365-2478.12720

Cited by 26 publications

(28 citation statements)

References 36 publications

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“…In general, strain rates below 2 μstrain/h during consolidation were considered sufficiently low to have almost no effect on the shale stiffness. For Opalinus Clay, however, the elastic properties no longer changed in a significant way for a consolidation strain rate below 50 μstrain/h (Lozovyi and Bauer, 2018).…”

Section: Samples and Testing Proceduresmentioning

confidence: 95%

From Static to Dynamic Stiffness of Shales: Frequency and Stress Dependence

Lozovyi

Bauer

2019

Rock Mech Rock Eng

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The relation between static and dynamic stiffness in shales is important for many engineering applications. Dynamic stiffness, calculated from wave velocities, is often related to static stiffness through simple empirical correlations. The reason for this is that dynamic properties are often easier to obtain; however, it is the static properties that define the actual subsurface response to stress or pore pressure changes. Rocks are not elastic media, and stiffness depends on the stress state, stress-change amplitude, loading rate, drainage conditions, fluid saturation, and scale. All these factors require consideration when static and dynamic stiffness properties are to be related. Two mechanisms that may have a strong effect on the stiffness of shales were studied in this experimental work: (i) a reduction of undrained static stiffness with an increase in stress amplitude and (ii) a frequency dependence (or dispersion) of dynamic stiffness. Laboratory tests were performed on four fully brine-saturated undrained field shales from different overburden formations. Experiments were conducted using a low-frequency apparatus-a triaxial loading cell with the ability to measure dynamic stiffness at seismic frequencies (1-150 Hz) and ultrasonic velocities (500 kHz). Shale anisotropy was characterized by testing differently oriented core plugs. Static and dynamic stiffness of shales The results demonstrated that all the tested shales exhibited a dispersion of dynamic stiffness from seismic to ultrasonic frequencies. Young's modulus dispersion for the tested shales ranged from nearly 30% to above 100%. Wave velocity dispersion was on the order of 10-20% for P-waves and 20-40% for S-waves. In static tests, the undrained rock stiffness gradually decreased with increasing stress amplitude. For one shale, the static undrained Young's modulus was reduced by 50% when amplitude of the loading-unloading measurement cycle was increased from 1 MPa to 3 MPa. This finding is explained by non-elastic deformations that increase with the stress level. A method of zero-stress extrapolation of static stiffness was used to obtain the purely elastic response. The stiffness for the limit of zero stresschange amplitude agreed well with the dynamic response at seismic frequency, providing a link between static and dynamic stiffness.

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Section: Samples and Testing Proceduresmentioning

confidence: 95%

From Static to Dynamic Stiffness of Shales: Frequency and Stress Dependence

Lozovyi

Bauer

2019

Rock Mech Rock Eng

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“…The representative parameters and fluid bulk modulus estimated from known temperature, pressure and salinity using Batzle and Wang equations (Batzle and Wang, 1992) are listed in Table 4. Figure 9 -Figure 18 show a comparison between optimized model and measurements for Jurassic shale sample provided by Hornby (1998), Kimmeridge shale sample provided by Hornby (1998), a shale sample ("Shale 2") provided by Hofmann (2006), Norwegian Sea shale sample provided by Dewhurst et al (2011), Mancos shale sample provided by Sarker and Batzle (2010), Opalinus Clay sample ("Shaly facies 3") provided by Lozovyi and Bauer (2019), Pierre shale sample with water saturation of 0.23 provided by Szewczyk et al (2018), Pierre shale sample with water saturation of 0.7 provided by Szewczyk et al (2018), D2 shale, and B3 shale provided by SINTEF, respectively. Interesting findings are as follows:…”

Section: Model Vs Experimental Datamentioning

confidence: 99%

“…In particular, shales often show strong elastic anisotropy that originates from the alignment and platy nature of its constituent minerals, as underpinned by laboratory measurements provided by many authors (e.g. Vernik and Nur, 1992;Wang, 2002b;Szewczyk et al, 2018;Lozovyi and Bauer, 2019). It has also been recognized that the elastic anisotropy has impact on seismic imaging (e.g., Thomsen, 1986), AVO (Amplitude Variation with Offset) response (e.g.…”

Section: Introductionmentioning

confidence: 98%

Rock Physics Model of Shale: Predictive Aspect

2021

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 A predictive rock model is developed based on the recently published Sayers-den Boer approach and compaction-dependent domain orientation  Anisotropy parameters delta and epsilon can be reasonably estimated from limited information using the model  Optimized parameters based on measured data, interplatelet medium properties, are consistent with the saturated fluid and existing studies Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

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“…Estimated Skempton's parameters are compared with existing measurement results. Holt et al (2018b) provided measured values for three shales, while Lozovyi and Bauer (2019) gave results for a shaly facies of Opalinus Clay. Skempton's parameters of the stiffer grain case are consistent with shale "B" and "M" of Holt et al (2018b) and the shaly facies of Lozovyi and Bauer (2019), while the anisotropic grain case is consistent with shale "D" of Holt et al (2018b).…”

Section: Comparison With Existing Measurementsmentioning

confidence: 99%

“…Shales often show strong elastic anisotropy that originates from the alignment and platy habit of its constituent minerals, as underpinned by existing laboratory measurements (e.g. Vernik and Nur 1992;Wang 2002;Szewczyk et al 2018;Lozovyi and Bauer 2019). Shale strength is also anisotropic, with less resistance for failure within the symmetry plane ("weak plane") than in other directions (e.g.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic Wellbore Stability Analysis: Impact on Failure Prediction

Asaka

Holt

2020

Rock Mech Rock Eng

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Shale formations are the main source of borehole stability problems during drilling operations. Suboptimal predictions of borehole failure may partly be caused by neglecting the anisotropic nature of shales: Conventional wellbore stability analysis is based on borehole stresses computed from isotropic linear elasticity (Kirsch solution) with the assumption of no induced pore pressure. This is very convenient for a practical implementation but does not always work for shales. Here, anisotropic wellbore stability analysis was performed targeting an offshore gas field to investigate in particular the impact of elastic anisotropy on borehole failure predictions. Stress concentration around a circular borehole in anisotropic shale was calculated by the Amadei solutions, and induced pore pressure was obtained from the Skempton parameters based on anisotropic poroelasticity. Borehole failure regions and modes were then predicted using the effective stresses and those are apparently consistent with observations. A comparison with the conventional approach suggests the importance of accounting for elastic anisotropy: Predicted failure regions, modes, and also the associated mud weight limits can be completely different. This observation may have significant implications for other fields since shale often show strong elastic anisotropy.

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Static and dynamic stiffness measurements with Opalinus Clay

Cited by 26 publications

References 36 publications

From Static to Dynamic Stiffness of Shales: Frequency and Stress Dependence

From Static to Dynamic Stiffness of Shales: Frequency and Stress Dependence

Rock Physics Model of Shale: Predictive Aspect

Anisotropic Wellbore Stability Analysis: Impact on Failure Prediction

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