Changes in seismic velocity and attenuation during deformation of granite

Lockner, D. A.; Walsh, J. B.; Byerlee, J. D.

doi:10.1029/jb082i033p05374

Cited by 217 publications

(139 citation statements)

References 14 publications

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“…There is ample experimental evidence to indicate the presence of preferred crack orientation in rocks (e.g., IIDA et al, 1967;GUPTA, 1973;WANG et al, 1975;LOCKNER et al, 1977;SOGA et al, 1978). Most previous theoretical calculations were made for an isotropic case in which cracks are assumed to be distributed and oriented spatially at random in an isotropic medium (e.g., WU, 1966;WALSH, 1969;KUSTER and TOKSOZ, 1974;BUDIANSKY and O'CONNELL, 1976).…”

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confidence: 99%

Seismic velocity anisotropy in a medium cotaining oriented cracks. Transversely isotropic case.

1982

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A new method was developed for calculating effective elastic parameters of a medium containing oblate spheroidal cracks having parallel planes. This new method is free from the restrictions of isotropic matrix material and low crack density. Velocity anisotropy was calculated for the case of oriented cracks filled with fluid. Effects of crack aspect ratio, fluid bulk modulus, and crack volume on velocity anisotropy were investigated. The present results showed smaller anisotropy than that given by ANDERSON et al. (1974) for a medium containing oriented spheroidal cracks. The relation between velocity and crack density parameter (ratio of porosity to aspect ratio of cracks divided

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confidence: 99%

Seismic velocity anisotropy in a medium cotaining oriented cracks. Transversely isotropic case.

1982

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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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“…Because the ordinate here is taken in the logarithmic scale, the dilatant strain is found to increase exponentially except just before the ultimate failure: 3.6 Elastic wave velocity variation Elastic wave velocities of rocks decrease when the samples are subjected to differential stress large enough to cause dilatancy. Many workers GUPTA, 1973;SPETZLER and MARTIN, 1974;LOCKNER et al, 1977;SOGA et al, 1978;SEYA et al, 1979;GRANRYD et al, 1983) have measured P-wave and Swave velocities of rocks during compressive loading.…”

Section: 5mentioning

confidence: 99%

Experimental study of strain-rate dependence and pressure dependence of failure properties of granite.

1987

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Effects of the strain rate and pressure on various brittle properties of granite under compressional loading are studied experimentally. Granite specimens were tested to failure under various constant strain rates at confining pressures of 0.1 to 200 MPa. The strain rates in these tests varied from 10-4 to 10-8 S s-1. The results show that the strength of granite decreases linearly as the logarithm of the strain rate decreases, and that the strain-rate dependence on the strength is enhanced at high confining pressures. The dilatant strain and elastic wave velocity variations with stress were found to be independent of the strain rate if the stress is normalized by the strength. The dilatant-strain-versus-stress curve is significantly affected by confining pressure but the confining pressure effect on the dilatant strain versus normalized stress is small. The acoustic emission rate is accelerated at a stress level closer to the failure strength as the strain rate decreases. Some of the timedependent properties are explained by a theory based on the concept of subcritical stress-corrosion cracking. But it is also clear that the stress-corrosion cracking theory does not provide reasonable explanations of the variation of acoustic emission rate with stress and the variation of strain with stress at the stage immediately before fracture.

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Changes in seismic velocity and attenuation during deformation of granite

Cited by 217 publications

References 14 publications

Seismic velocity anisotropy in a medium cotaining oriented cracks. Transversely isotropic case.

Seismic velocity anisotropy in a medium cotaining oriented cracks. Transversely isotropic case.

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

Experimental study of strain-rate dependence and pressure dependence of failure properties of granite.

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