Wave dispersion and attenuation due to multi-scale wave-induced fluid flow in layered partially saturated pore-crack media

2022 ◽  
Vol 208 ◽  
pp. 109447
Author(s):  
Miaomiao Xu ◽  
Xingyao Yin ◽  
Zhaoyun Zong
Keyword(s):  
Fluid Flow ◽  
Wave Dispersion ◽  
Multi Scale ◽  
Partially Saturated ◽  
Wave Induced ◽  
Dispersion And Attenuation

Impact of fluid saturation on the reflection coefficient of a poroelastic layer

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. N1-N12 ◽  
Author(s):  
Beatriz Quintal ◽  
Stefan M. Schmalholz ◽  
Yuri Y. Podladchikov
Keyword(s):  
Fluid Flow ◽  
Reflection Coefficient ◽  
Analytical Solution ◽  
Quality Factor ◽  
Velocity Dispersion ◽  
Normal Incidence ◽  
Sand Layer ◽  
Partially Saturated ◽  
Fluid Saturation ◽  
Wave Induced

The impact of changes in saturation on the frequency-dependent reflection coefficient of a partially saturated layer was studied. Seismic attenuation and velocity dispersion in partially saturated (i.e., patchy saturated) poroelastic media were accounted for by using the analytical solution of the 1D White’s model for wave-induced fluid flow. White’s solution was applied in combination with an analytical solution for the normal-incidence reflection coefficient of an attenuating layer embedded in an elastic or attenuating background medium to investigate the effects of attenuation, velocity dispersion, and tuning on the reflection coefficient. Approximations for the frequency-dependent quality factor, its minimum value, and the frequency at which the minimum value of the quality factor occurs were derived. The approximations are valid for any two alternating sets of petrophysical parameters. An approximation for the normal-incidence reflection coefficient of an attenuating thin (compared to the wavelength) layer was also derived. This approximation gives insight into the influence of contrasts in acoustic impedance and/or attenuation on the reflectivity of a thin layer. Laboratory data for reflections from a water-saturated sand layer and from a dry sand layer were further fit with petrophysical parameters for unconsolidated sand partially saturated with water and air. The results showed that wave-induced fluid flow can explain low-frequency reflection anomalies, which are related to fluid saturation and can be observed in seismic field data. The results further indicate that reflection coefficients of partially saturated layers (e.g., hydrocarbon reservoirs) can vary significantly with frequency, especially at low seismic frequencies where partial saturation may often cause high attenuation.

FRACTAL WAVEFIELD ANALYSIS TO CHARACTERIZE GEOMETRIC PROPERTIES OF FRACTURED MEDIA

Fractals ◽  
2007 ◽  
Vol 15 (02) ◽  
pp. 127-138
Author(s):  
ALEXANDER DROUJININE ◽  
VLADIMIR ROK
Keyword(s):  
Homogeneous Medium ◽  
Wave Dispersion ◽  
Analytic Solutions ◽  
Body Waves ◽  
Fracture Detection ◽  
Fracture Characterization ◽  
Multi Scale ◽  
Poroelastic Media ◽  
Inverse Q Filtering ◽  
Dispersion And Attenuation

We have investigated wave scattering by chaotic fractured systems of fractal geometry with random spatial variation that causes energy loss of the directly propagated field. We have examined simple analytic solutions in fractal poroelastic media. These solutions may be characterized by their frequency-power-law (FPL) signature caused by wave dispersion and attenuation. It has been proved that medium memory effects cause smoothing of the wavefield in the vicinity of the wavefront and rapid amplitude decay far from the wavefront. It appears that finite-bandwidth signals are delayed with respect to the wavefront in comparable elastic media. To examine the FPL dependence of direct body waves propagating in a homogeneous medium containing fractal inhomogeneities, we compute acoustic finite-difference snapshots in the frequency range f = 20 - 200 Hz. Numerical results show that the fractal dimension can be estimated from the FPL dependence of the scattered wavefield. Applications to fracture characterization are considered. Results are important for multi-scale depth imaging, inverse Q filtering, fracture detection, and integrated geophysical reservoir monitoring.

scholarly journals A New Anelasticity Model for Wave Propagation in Partially Saturated Rocks

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7619
Author(s):  
Chunfang Wu ◽  
Jing Ba ◽  
Xiaoqin Zhong ◽  
José M. Carcione ◽  
Lin Zhang ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Ordos Basin ◽  
Rock Properties ◽  
Tight Sandstone ◽  
Reservoir Rocks ◽  
Multi Scale ◽  
Partially Saturated ◽  
Single Scale ◽  
Confining Pressures ◽  
Dispersion And Attenuation

Elastic wave propagation in partially saturated reservoir rocks induces fluid flow in multi-scale pore spaces, leading to wave anelasticity (velocity dispersion and attenuation). The propagation characteristics cannot be described by a single-scale flow-induced dissipation mechanism. To overcome this problem, we combine the White patchy-saturation theory and the squirt flow model to obtain a new anelasticity theory for wave propagation. We consider a tight sandstone Qingyang area, Ordos Basin, and perform ultrasonic measurements at partial saturation and different confining pressures, where the rock properties are obtained at full-gas saturation. The comparison between the experimental data and the theoretical results yields a fairly good agreement, indicating the efficacy of the new theory.

Extended Gassmann Equation with Dynamic Volumetric Strain: Modeling Wave Dispersion and Attenuation of Heterogenous Porous Rocks

Geophysics ◽  
2021 ◽  
pp. 1-97
Author(s):  
Luanxiao Zhao ◽  
Yirong Wang ◽  
Qiuliang Yao ◽  
Jianhua Geng ◽  
Hui Li ◽  
...  
Keyword(s):  
Fluid Pressure ◽  
Volumetric Strain ◽  
Wave Dispersion ◽  
Heterogeneous Porous Media ◽  
Porous Rocks ◽  
Analytical Methodology ◽  
Heterogeneous Rocks ◽  
Rock Characterization ◽  
Wave Induced ◽  
Dispersion And Attenuation

Sedimentary rocks are often heterogeneous porous media inherently containing complex distributions of heterogeneities (e.g., fluid patches, cracks). Understanding and modeling their frequency-dependent elastic and adsorption behaviors is of great interest for subsurface rock characterization from multi-scale geophysical measurements. The physical parameter of dynamic volumetric strain (DVS) associated with wave-induced fluid flow is proposed to understand the common physics and connections behind known poroelastic models for modeling dispersion behaviors of heterogeneous rocks. We derive the theoretical formulations of DVS for patchy saturated rock at mesoscopic scale and cracked porous rock at microscopic grain scales, essentially embodying the wave-induced fluid pressure relaxation process. By incorporating the DVS into the classical Gassmann equation, a simple but practical “dynamic equivalent” modeling approach, extended Gassmann equation, is developed to characterize the dispersion and attenuation of complex heterogeneous rocks at non-zero frequencies. Using the extended Gassmann equation, the effect of microscopic or mesoscopic heterogeneities with complex distributions on the wave dispersion and attenuation signatures can be captured. The proposed theoretical framework provides a simple and straightforward analytical methodology to calculate wave dispersion and attenuation in porous rocks with multiple sets of heterogeneities exhibiting complex characteristics. We also demonstrate that, with the appropriate consideration of multiple crack sets and complex fluids patches distribution, the modeling results can better interpret the experimental data sets of dispersion and attenuation for heterogeneous porous rocks.

scholarly journals Attenuation of Seismic Waves in Partially Saturated Berea Sandstone as a Function of Frequency and Confining Pressure

2021 ◽  
Vol 9 ◽  
Author(s):  
Nicola Tisato ◽  
Claudio Madonna ◽  
Erik H. Saenger
Keyword(s):  
Fluid Flow ◽  
Wave Attenuation ◽  
Confining Pressure ◽  
Berea Sandstone ◽  
Experimental Conditions ◽  
Frequency Dependent ◽  
Near Surface ◽  
Partially Saturated ◽  
Near Surface Geophysics ◽  
Wave Induced

Frequency-dependent attenuation (1/Q) should be used as a seismic attribute to improve the accuracy of seismic methods and imaging of the subsurface. In rocks, 1/Q is highly sensitive to the presence of saturating fluids. Thus, 1/Q could be crucial to monitor volcanic and hydrothermal domains and to explore hydrocarbon and water reservoirs. The experimental determination of seismic and teleseismic attenuation (i.e., for frequencies < 100 Hz) is challenging, and as a consequence, 1/Q is still uncertain for a broad range of lithologies and experimental conditions. Moreover, the physics of elastic energy absorption (i.e., 1/Q) is often poorly constrained and understood. Here, we provide a series of measurements of seismic wave attenuation and dynamic Young’s modulus for dry and partially saturated Berea sandstone in the 1–100 Hz bandwidth and for confining pressure ranging between 0 and 20 MPa. We present systematic relationships between the frequency-dependent 1/Q and the liquid saturation, and the confining pressure. Data in the seismic bandwidth are compared to phenomenological models, ultrasonic elastic properties and theoretical models for wave-induced-fluid-flow (i.e., squirt-flow and patchy-saturation). The analysis suggests that the observed frequency-dependent attenuation is caused by wave-induced-fluid-flow but also that the physics behind this attenuation mechanism is not yet fully determined. We also show, that as predicted by wave-induced-fluid-flow theories, attenuation is strongly dependent on confining pressure. Our results can help to interpret data for near-surface geophysics to improve the imaging of the subsurface.

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