Experiments on stress dependent borehole acoustic waves

Hsu, Chaur-Jian; Kane, M.; Winkler, Kenneth W.; Wang, Canyun; Johnson, David Linton

doi:10.1121/1.3624819

Cited by 8 publications

(3 citation statements)

References 24 publications

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“…This would imply that the quadrupole dispersion is essentially insensitive to near-wellbore effects for the cases considered, even when the spatial variation of shear velocities is quite significant near the borehole. This is consistent with approximations derived from perturbation analyses (Sinha et al, 2003) and recent experimental results (Hsu et al, 2011).…”

Section: Velocity Distribution and Quadrupole Wave Dispersionsupporting

confidence: 91%

Novel finite-element approach applied to borehole quadrupole dispersion analysis in stress-sensitive formations

Jørgensen

Burns

2013

GEOPHYSICS

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Near a borehole, stress concentration effects may cause a complex spatial variation of elastic anisotropy. Stress-induced sonic anisotropy results when moduli and velocities are stress dependent and the state of stress is nonhydrostatic. For such cases, the appropriate material model is that of an elastic orthorhombic medium with material axes aligned with the principal axes of stress. We simulate the dispersion characteristics of quadrupole waves propagating along a borehole in a stress-sensitive formation. To include sensitivity to stress in the analysis, we derive a finite-element modeling approach which includes the stress-velocity relationship, the perturbed stress and velocity field near the borehole, and solutions to the full coupled anisotropic and 3D wave equation. We characterized the anisotropy around the borehole for different in situ stress conditions, and we derived the effects on quadrupole dispersion characteristics. Of particular interest was the phase velocity of the quadrupole wave, which at low frequencies provides an estimate of formation shear-wave velocity. Results indicated that the quadrupole mode dispersion was relatively insensitive to the hoop stress effects around a borehole giving greater confidence to shear-wave estimates made from these modes. The proposed ring-element formulation, which includes Fourier expansions of the field variables in the direction of the circumference, is well suited to this analysis and can be adapted to include other effects, such as a finite-length borehole.

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Section: Velocity Distribution and Quadrupole Wave Dispersionsupporting

confidence: 91%

Novel finite-element approach applied to borehole quadrupole dispersion analysis in stress-sensitive formations

Jørgensen

Burns

2013

GEOPHYSICS

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“…; Hsu et al . ) and field (Balland and Renaud ) to induce considerable azimuthal variations in the compressional and shear wave speeds. These azimuthal variations are also referred to as an “anisotropy”, but while it is related to the formation anisotropy due to mineral, crack, and fracture alignment, layering, or in situ stress, one must be aware that stress concentrations contribute to these additional changes in the material properties around the borehole (Plona et al .…”

Section: Resultsmentioning

confidence: 99%

Static and dynamic pressure sensitivity anisotropy of a calcareous shale

Ong

Schmitt

Kofman

et al. 2016

Geophysical Prospecting

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Optimizing the productivity of nonconventional, low‐permeability “shale” reservoirs requires detailed knowledge of the mechanical properties of such materials. These rocks' elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information. Here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional Duvernay reservoir of Alberta, Canada. The complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 MPa. Wave speed anisotropies of up to 35% are observed at even the highest confining pressures. Furthermore, the stress sensitivity of the wave speeds, and hence moduli, is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure, whereas those along the bedding plane show, unexpectedly, nearly no pressure dependence. These observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images. These results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions, for the concentration of stress within such formations, and for estimation of static engineering moduli from sonic log wave speeds.

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“…Generally, the observed seismic records result from both source and propagation effects. The effect of prestress on the propagation of elastic waves is widely investigated in seismology (Harkrider et al., 1994; Tromp & Trampert, 2018; Walton, 1973; Zatsepin & Crampin, 1997) and borehole geophysics (Hsu et al., 2011; Liu et al., 2019; Sayers, 2007; Schmitt et al., 2012; Sinha & Kostek, 1996; Wang & Tang, 2005). Moreover, the literature describing seismic sources in unstressed media can refer to the groundbreaking work of Burridge and Knopoff (1964).…”

Section: Introductionmentioning

confidence: 99%

Seismic Sources in Stress‐Induced Anisotropic Media

2022

JGR Solid Earth

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Rocks in the upper mantle are extensively subjected to initial stress. The rock exhibits elastic anisotropy under the deviatoric stress, which affects the seismic response of underground structures. This paper aims to study the effect of stress‐induced anisotropy on the seismic source. The seismic moment tensor generated by a shear faulting in a homogeneous isotropic medium with initial stress is derived by using the motion description in the intermediate configuration, the constitutive relation of third‐order elasticity, and the boundary condition considering the effect of initial stress. Then the seismic moment tensor is decomposed to investigate seismic source characters quantitatively. Our results show that shear faulting in a stress‐induced anisotropic medium can produce significant non‐double‐couple (non‐DC) mechanisms, including compensated linear vector dipole (CLVD) and isotropic (ISO) components. ISO and CLVD components vary linearly with the initial shear stress on faults. In addition, stress‐induced anisotropy causes the double‐couple (DC) to deviate from the plane defined by the fault normal and slip direction. The initial stress not only affects the source intensity but also affects the propagation of seismic waves. The radiation patterns of longitudinal waves have non‐uniform lobes, which shows the characteristic of anisotropy. Stress‐induced anisotropic parameters are smaller than intrinsic anisotropy at high‐stress levels and a nearly linear function of the increased initial stress. These results underscore the importance of considering stress‐induced anisotropy in the inversion of focal mechanisms and provide a new perspective for monitoring underground stress.

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Experiments on stress dependent borehole acoustic waves

Cited by 8 publications

References 24 publications

Novel finite-element approach applied to borehole quadrupole dispersion analysis in stress-sensitive formations

Novel finite-element approach applied to borehole quadrupole dispersion analysis in stress-sensitive formations

Static and dynamic pressure sensitivity anisotropy of a calcareous shale

Seismic Sources in Stress‐Induced Anisotropic Media

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