Research note: Seismic attenuation due to wave‐induced fluid flow at microscopic and mesoscopic scales

Rubino, J. Germán; Holliger, Klaus

doi:10.1111/1365-2478.12009

Cited by 41 publications

(32 citation statements)

References 22 publications

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“…Although part of this intrinsic anisotropy may be due to the presence of microcracks, squirt flow effects are neglected in the modeling. However, as pointed out by Rubino and Holliger (), it is possible to account for squirt flow attenuation due to the presence of fluid‐saturated microcracks in the background by allowing the dry frame background stiffness coefficients to be complex valued and frequency dependent. It is also worth noting that although we have used Gassmann's () equations to relate the stiffness coefficients for the dry and saturated frame, a more generic approach may be needed depending on the nature of the considered intrinsic anisotropy.…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of Seismic Attenuation and Phase Velocity to Intrinsic Background Anisotropy in Fractured Porous Rocks: A Numerical Study

et al. 2017

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Many researchers have analyzed seismic attenuation and velocity dispersion due to wave‐induced fluid flow (WIFF) related to the presence of fluid‐saturated fractures embedded in an isotropic porous background. Most fractured formations do, however, exhibit some degree of intrinsic elastic and hydraulic anisotropy of the background, and the impact of which on the effective seismic properties remains largely unexplored. In this work, we extend a numerical upscaling procedure to account for the potential intrinsic elastic and hydraulic anisotropy of the background. To do this, we represent the background of a representative sample of the fractured formation of interest with an anisotropic poroelastic medium and apply a set of relaxation experiments to compute the effective anisotropic seismic properties. A comprehensive numerical analysis allows us to observe that, for samples containing hydraulically connected fractures, the anisotropic behavior of both P and S waves differs significantly from that observed for an isotropic background. The anisotropy of the stiffness of the background plays a fundamental role for WIFF between the fractures and the background as well as for WIFF between connected fractures. Conversely, the anisotropy of the background permeability affects the characteristic frequency, the angle dependence, and the magnitude of the effects related to WIFF between fractures and background. In addition, different correlations between hydraulic and elastic background anisotropy lead to different degrees of effective seismic anisotropy. Our results therefore indicate that accounting for the effects of intrinsic background anisotropy on WIFF is crucial for a quantitative interpretation of seismic anisotropy measurements in fluid‐saturated fractured formations.

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Section: Discussionmentioning

confidence: 99%

Sensitivity of Seismic Attenuation and Phase Velocity to Intrinsic Background Anisotropy in Fractured Porous Rocks: A Numerical Study

et al. 2017

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“…In other words, the observed dispersion corresponds to the undrained/unrelaxed transition. The pore-scale squirt flow between pores of different shapes and orientations is believed the main cause for the undrained/unrelaxed transition (Rubino & Holliger, 2013). We compared the measurement results with the squirt-flow model provided by Gurevich et al (2010).…”

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confidence: 99%

Pressure and Fluid Effect on Frequency‐Dependent Elastic Moduli in Fully Saturated Tight Sandstone

et al. 2017

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We developed a system to explore the effects of pressure and fluid viscosity on the dispersion and attenuation of fully saturated tight sandstones, especially at seismic frequencies. Calibration of the new system revealed that the system can operate reliably at frequencies of [2–200, 106] Hz. Tight sandstone with a “crack–pore” microstructure was tested under nitrogen gas (dry), brine, and glycerin saturation. A frequency‐dependent effect was not found for the dry case. However, apparent dispersion and attenuation for the undrained/unrelaxed transition was clearly observed for sample under brine or glycerin saturation, the magnitude of which was largely suppressed by increasing effective pressure. The measurement results illustrated that increasing the fluid viscosity or the effective pressure will shift the dispersion curve to the lower frequency range. A simple squirt‐flow model with dual‐porosity scheme was used to compare with the measurement results. Although the estimated values deviated slightly from the data, the trend fitted the saturated data relatively well, especially at low effective pressures. Therefore, considering the crack–pore microstructure of the tight sandstone, dispersion and attenuation are induced predominantly by the squirt‐flow stiffening effect from cracks to pores.

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“…V P dispersion highly depends on the subsurface geology and can be fed into numerical models for better understanding of rock physical properties. For example, V P dispersion in sediments with high gas hydrate concentration has two f c , mimicking the numerical results for media with both microscopic and mesoscopic fluid flows (Rubino and Holliger ) or with connected fractures (Rubino et al . ; Fig.…”

Section: Discussionmentioning

confidence: 61%

“…For more complicated models, numerical simulation can be used. For example, Rubino and Holliger () modelled Q –1 and V in a medium with both microscopic and mesoscopic fluid flows induced by seismic waves; Rubino et al . () modelled the effects of fracture connectivity.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of velocity dispersion using full‐waveform multichannel sonic logging data: A case study

Sun

Milkereit

Tisato

2016

Geophysical Prospecting

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Seismic attenuation and velocity dispersion are potentially able to reveal the rock physical properties of the subsurface. Conventionally, a frequency‐independent quality factor (Q) is measured. This Q is equivalent to the total velocity dispersion in a seismic record and is inadequate for analysing the attenuation mechanism or rock physical properties. Here a new method is proposed to extract the velocity dispersion curves so that more attributes can be obtained from full‐waveform multichannel sonic logging data, especially the critical frequency (fc) if it is within the bandwidth of the data. This method first decomposes the seismic data into a series of frequency components, computes the semblance of each frequency component for different velocity values, cross‐correlates the semblance matrices of adjacent frequency components to get the velocity gradients, and finally integrates to obtain a velocity dispersion curve. Results of this method are of satisfactory accuracy and robustness. This method is applied to the data acquired in Mallik 5L‐38 gas hydrate research well in Mackenzie Delta, Northwest Territories, Canada. The observed P‐wave velocity dispersion compares well with the geological setting. In the gas hydrate zone (about 900 m–1100 m), high concentration of gas hydrate causes very strong velocity dispersion and a distinct fc at about 15 kHz, likely due to strong scattering of centimetre‐scale inclusions of gas hydrate; concurrently, water flow in connected cracks in some ranges of this zone adds a large part of velocity dispersion and a dimmer fc at about 9.5 kHz. Immediate underneath the gas hydrate zone, abundant free water in weakly laminated sediments causes quite strong velocity dispersion and an fc at about 6.5 kHz. Velocity dispersion is mild and without an obvious fc in sediments above the gas hydrate zone.

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Research note: Seismic attenuation due to wave‐induced fluid flow at microscopic and mesoscopic scales

Cited by 41 publications

References 22 publications

Sensitivity of Seismic Attenuation and Phase Velocity to Intrinsic Background Anisotropy in Fractured Porous Rocks: A Numerical Study

Sensitivity of Seismic Attenuation and Phase Velocity to Intrinsic Background Anisotropy in Fractured Porous Rocks: A Numerical Study

Pressure and Fluid Effect on Frequency‐Dependent Elastic Moduli in Fully Saturated Tight Sandstone

Analysis of velocity dispersion using full‐waveform multichannel sonic logging data: A case study

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