Experimental verification of stress‐induced anisotropy

Cruts, Helma M. A.; Groenenboom, Jeroen; Duijndam, A. J. W.; Fokkema, J.T.

doi:10.1190/1.1887537

Cited by 30 publications

(11 citation statements)

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“…The laboratory experiments of Cruts et al (1995), measuring 1 MHz shear waves in triaxially-stressed 20 cm sandstone cubes, also confirmed that (comparatively) small changes of strain modify microcrack geometry to produce changes in shear-wave splitting. These experiments were on dry specimens (the "drained" condition, Zatsepin and Crampin, 1997).…”

Section: Introductionmentioning

confidence: 68%

“…Consequently, almost all rocks contain distributions of stress-aligned fluid-filled intergranular EDA-cracks (Crampin, 1994). Field observations (see references in INTRODUCTION), laboratory experiments (King et al, 1994;Cruts et al, 1995), and numerical modelling with APE Crampin, 1995, 1997;Crampin andZatsepin, 1995, 1997) suggest that the microcrack geometry, in particular crack aspect ratio, is critically sensitive to small changes in strain. Such changes are almost transparent to P-wave propagation, but shear-wave splitting carries detailed three-dimensional information about the EDA-crack geometry along the ray path (Crampin, 1981).…”

Section: Universalitymentioning

confidence: 99%

See 1 more Smart Citation

Changes of Strain before Earthquakes: The Possibility of Routine Monitoring of Both Long-Term and Short-Term Precursors.

Crampin¹,

Zatsepin²

1997

J,Phys,Earth

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Earthquakesare extraordinarily complicated phenomena and deterministic prediction of the magnitude, time and place of large earthquakes is likely to be intrinsically impossible. A more simple phenomenon, the build up of deformation which leads to the earthquake, can be monitored by the behaviour of seismic shear waves, and this offers a way of forecasting the proximity of large earthquakes. Recent results, including field observations of shear waves before earthquakes, laboratory experiments with stress cells, and theoretical modelling of microscale deformation, demonstrate that long-term precursory build-up of deformation can be monitored for some years before a large earthquake. There may even be the possibility of identifying short-term precursors a few hours or days before the earthquake. This paper suggests that reliable routine earthquake forecasting would require controlled seismic experiments between a specific pattern of deep wells.

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Section: Introductionmentioning

confidence: 68%

Section: Universalitymentioning

confidence: 99%

Changes of Strain before Earthquakes: The Possibility of Routine Monitoring of Both Long-Term and Short-Term Precursors.

Crampin¹,

Zatsepin²

1997

J,Phys,Earth

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“…When the crack population is anisotropic, either in the original unstressed condition, or as a result of the stress field, then these can impact the overall elastic anisotropy of the rock. Laboratory demonstrations of stress-induced anisotropy have been reported by numerous authors (e.g., Lockner et al, 1977;Zamora and Poirier, 1990;and Sayers et al, 1990;Yin, 1992;Cruts et al, 1995).…”

Section: Stress-induced Velocity Anisotropymentioning

confidence: 99%

Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

Mavko¹

2000

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JUSTIFICATIONDuring Phase I, we performed our rock physics, geologic, and seismic feasibility analysis for fracture characterization. We addressed the problem of seismic fracture detection and characterization, in general, and specifically at our field site in West Texas. In this analysis, we were able to implement a number of fracture modeling procedures and to quantitatively assess the theoretical detectability of reservoir fractures. This allowed us to identify which of the several seismic attributes are most likely to be useful for fracture detection at the site. One of our results showed that Thomsen's parameters should be very useful for indicating gas-filled fractures at the site. We also outlined Monte Carlo approaches that can be applied for feasibility analysis at any site.Prior to our study, most seismic fracture detection methods have focused on qualitatively detecting seismic anisotropy. While anisotropy is critical, when used alone it has left us with interpretation ambiguities and nonuniqueness. During Phase 1 of this project, we found that by statistically integrating geologic and seismic information we can develop nontraditional methods for fracture detection. For example, we found that quantifying the correlations between fracture occurrence and depositional environment, and between fracture spacing and layer thickness, we allow us to decrease the uncertainty of fracture interpretation using seismic anisotropy. One of the reasons for this is that different depositional environments (and rock facies) give rise to differences in their seismic signatures (impedances, velocities, and Poisson's ratio.Phase II will allow us to validate and improve these methodologies by carrying out a smallscale field pilot study. Taking methods to the field, always allows us to make them more applicable. In the field, we will be able to more accurately assess the uncertainties introduced by measurement noise, source and receiver response, coupling, and near surface acoustic properties. We can then more realistically develop ways to reduce the uncertainty, as well as to identify which aspects of the geology and fracture distribution we can characterize most robustly. The small-scale field study will also help us to establish empirical fracture parameters that are needed as inputs to rock physics models. For example, ALL of the effective medium models for fracture-induced anisotropy require fracture stiffness as inputs (these are sometimes characterized as moduli or aspect ratios). There is no realistic way to assign these values DOE FINAL TECHNICAL REPORT ON PHASE 4 theoretically, so being able to calibrate them in a small pilot will give us the critical inputs we need for interpreting the full scale seismic survey in phase III. Finally, the data from the pilot will allow us to add an aspect of "data mining" to the study. In Phase I, we have exploited our best theoretical tools, but the real field data will give us the opportunity to discover other, unpredicted, signatures of fractures that might prove valuable.Our a...

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“…For instance, acoustic measurements in granites (Nur and Simmons, 1969), sandstone (Cruts et al, 1995), and soils Zeng, 1999; have shown that P-and S-wave velocities (Vp and Vs, respectively) depend on the angle between the applied stress and wave propagation and polarization. Cruts et al (1995) found shear birefringence in the symmetry plane when the stress pattern is anisotropic. In addition, velocity anisotropy can be more sensitive to stress in soft sediments than in consolidated rocks .…”

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

“…Research in soft sediments and stress anisotropy has been done on static properties, such as Young modulus, stress versus strain, strength (Wong and Arthur, 1985;Jiang et al, 1997;Hoque and Tatsuoka, 1998). Research on stress-induced anisotropy of dynamic properties, i.e., acoustic velocities, has been done for a wide range of compressive stresses in consolidated rocks (Nur and Simmons, 1969;Best et al, 1994;Cruts et al, 1995;Furre et al, 1995;). In contrast, in soft sediments, stress-induced velocity anisotropy has been studied only at low compressive stresses up to 8 bars Zeng, 1999;.…”

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Mavko¹

2006

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Summary of Accomplishments and ResultsWe completed our planned work on anisotropy in loose unconsolidated sediments.An important accomplishment was to understand the seismic velocity anisotropy resulting from the combined roles of depositional stratification and stress in unconsolidated sands. This work has lead to one Ph.D. dissertation, and two conference presentations (SEG, 2003). The expanded abstracts from the conference proceedings were attached in the annual report for [2003][2004]. The completed Ph.D. dissertation is forms part of this final report as attachment A.The dissertation presents an experimental study of velocity anisotropy in unconsolidated sands at measured compressive stresses up to 40 bars, which correspond to the first hundred meters of the subsurface. Two types of velocity anisotropy are considered, that due to intrinsic textural anisotropy, and that due to stress anisotropy.Three types of tests were performed: (1) hydrostatic pressure, (2) quasihydrostatic stress, in which, cubic samples are placed in the polyaxial cell and approximately equal forces are applied in each of the three principal directions; and (3) uniaxial strain, in which, cubic samples are placed in the polyaxial cell and an axial stress is applied in the Zdirection, while the horizontal platens are held fixed, at approximately zero displacement. The hydrostatic pressure test is used to compare the standard velocity measurements with the velocity anisotropy measured in the polyaxial cell. The quasi-hydrostatic stress test is used to study the velocity anisotropy resulting from intrinsic anisotropy of the granular materials. The uniaxial strain test is used to study the velocity anisotropy resulting from stress anisotropy in sands. We found that intrinsic and stress-induced anisotropy can be detected in sands using Vp. The intrinsic velocity anisotropy was studied using P-wave velocities and the textural anisotropy was studied using the spatial autocorrelation function of sediment images for sands and glass beads. The results suggest that P-wave velocity anisotropy and textural anisotropy are related for grain segregation or stratification. We found that sand samples display a bi-linear dependence of velocity anisotropy with stress anisotropy. There exists a transition stress beyond which the stressinduced anisotropy outweighs the intrinsic anisotropy for three different sands. In addition, the dissertation discusses the problem of extrapolating acoustic velocities measured under hydrostatic pressure to quasi-hydrostatic stress. Measured Vp under hydrostatic pressure is higher than Vp measured under quasi-hydrostatic stress in the sand, for the same depositional anisotropy and similar isotropic stress. This difference might be due to boundary effects in the apparatus, and due to complexity of the stress field inside of the granular material samples. Finally, we found that the model of Norris I find that intrinsic and stress-induced anisotropy can be detected in sands using Vp. I study the intrinsic velocity anisotropy usi...

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Experimental verification of stress‐induced anisotropy

Cited by 30 publications

References 1 publication

Changes of Strain before Earthquakes: The Possibility of Routine Monitoring of Both Long-Term and Short-Term Precursors.

Changes of Strain before Earthquakes: The Possibility of Routine Monitoring of Both Long-Term and Short-Term Precursors.

Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

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