scholarly journals Effect of Fracture Aperture on P-Wave Attenuation: A Seismic Physical Modelling Study

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Aniekan Martin Ekanem ◽  
Xiang Yang Li ◽  
Mark Chapman ◽  
Main Ian ◽  
Jianxin Wei
Keyword(s):  
Wave Attenuation ◽  
Physical Modelling ◽  
Spectral Ratio ◽  
P Wave ◽  
Scale Model ◽  
Ratio Method ◽  
Fracture Aperture ◽  
Water Tank ◽  
Fracture Density ◽  
Transmission Method

We used the seismic physical modelling approach to study the effect of fracture thickness or aperture on P-wave attenuation, using a laboratory scale model of two horizontal layers. The first layer is isotropic while the second layer has six fractured blocks, each consisting of thin penny-shaped chips of 3 mm fixed diameter and same thickness to simulate a set of aligned vertical fractures. The thickness of the chips varies according to the blocks while the fracture density remains the same in each block. 2D reflection data were acquired with the physical model submerged in a water tank in a direction perpendicular to the fracture strikes using the pulse and transmission method. The induced attenuation was estimated from the preprocessed CMP gathers using the QVO method, which is an extension of the classical spectral ratio method of attenuation measurement from seismic data. The results of our analysis show a direct relationship between attenuation and the fracture thickness or aperture. The induced attenuation increases systematically with fracture thickness, implying more scattering of the wave energy in the direction of increasing aperture. This information may be useful to differentiate the effect caused by thin microcracks from that of large open fractures.

scholarly journals Seismic wave attenuation in the uppermost glacier ice of Storglaciären, Sweden

2010 ◽  
Vol 56 (196) ◽  
pp. 249-256 ◽  
Author(s):  
Alessio Gusmeroli ◽  
Roger A. Clark ◽  
Tavi Murray ◽  
Adam D. Booth ◽  
Bernd Kulessa ◽  
...  
Keyword(s):  
Seismic Wave ◽  
Wave Attenuation ◽  
Seismic Refraction ◽  
Spectral Ratio ◽  
P Wave ◽  
Ratio Method ◽  
Polar Ice ◽  
Seismic Line ◽  
Seismic Wave Attenuation ◽  
Glacier Ice

AbstractWe conducted seismic refraction surveys in the upper ablation area of Storglaciären, a small valley glacier located in Swedish Lapland. We estimated seismic-wave attenuation using the spectral-ratio method on the energy travelling in the uppermost ice with an average temperature of approximately −1 °C. Attenuation values were derived between 100 and 300 Hz using the P-wave quality factor, QP, the inverse of the internal friction. By assuming constant attenuation along the seismic line we obtained mean QP = 6 ± 1. We also observed that QP varies from 8 ± 1 to 5 ± 1 from the near-offset to the far-offset region of the line, respectively. Since the wave propagates deeper at far offsets, this variation is interpreted by considering the temperature profile of the study area; far-offset arrivals sampled warmer and thus more-attenuative ice. Our estimates are considerably lower than those reported for field studies in polar ice (∼500–1700 at −28°C and 50–160 at −10°C) and, hence, are supportive of laboratory experiments that show attenuation increases with rising ice temperature. Our results provide new in situ estimates of QP for glacier ice and demonstrate a valuable method for future investigations in both alpine and polar ice.

scholarly journals Event couple spectral ratio Q method for earthquake clusters: application to North-West Bohemia

2018 ◽  
Author(s):  
Marius Kriegerowski ◽  
Simone Cesca ◽  
Matthias Ohrnberger ◽  
Torsten Dahm ◽  
Frank Krüger
Keyword(s):  
Wave Attenuation ◽  
Attenuation Factor ◽  
Source Region ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Earthquake Swarms ◽  
North West ◽  
High Attenuation ◽  
West Bohemia ◽  
Spectral Ratio Method

Abstract. We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q−1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wavefield seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms, but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to North-West Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp 

P-wave attenuation anisotropy in fractured media: A seismic physical modelling study

2012 ◽  
Vol 61 ◽  
pp. 420-433 ◽  
Author(s):  
A.M. Ekanem ◽  
J. Wei ◽  
X.-Y. Li ◽  
M. Chapman ◽  
I.G. Main
Keyword(s):  
Wave Attenuation ◽  
Physical Modelling ◽  
Fractured Media ◽  
P Wave ◽  
Attenuation Anisotropy ◽  
Modelling Study

Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. D1-D7 ◽  
Author(s):  
Yaping Zhu ◽  
Ilya Tsvankin ◽  
Pawan Dewangan ◽  
Kasper van Wijk
Keyword(s):  
Attenuation Coefficient ◽  
Symmetry Axis ◽  
Wave Attenuation ◽  
Transversely Isotropic ◽  
P Wave ◽  
Velocity Variation ◽  
Ratio Method ◽  
Fracture Detection ◽  
Wide Range ◽  
Attenuation Anisotropy

Anisotropic attenuation can provide sensitive attributes for fracture detection and lithology discrimination. This paper analyzes measurements of the P-wave attenuation coefficient in a transversely isotropic sample made of phenolic material. Using the spectral-ratio method, we estimate the group (effective) attenuation coefficient of P-waves transmitted through the sample for a wide range of propagation angles (from [Formula: see text] to [Formula: see text]) with the symmetry axis. Correction for the difference between the group and phase angles and for the angular velocity variation help us to obtain the normalized phase attenuation coefficient [Formula: see text] governed by the Thomsen-style attenuation-anisotropy parameters [Formula: see text] and [Formula: see text]. Whereas the symmetry axis of the angle-dependent coefficient [Formula: see text] practically coincides with that of the velocity function, the magnitude of the attenuation anisotropy far exceeds that of the velocity anisotropy. The quality factor [Formula: see text] increases more than tenfold from the symmetry axis (slow direction) to the isotropy plane (fast direction). Inversion of the coefficient [Formula: see text] using the Christoffel equation yields large negative values of the parameters [Formula: see text] and [Formula: see text]. The robustness of our results critically depends on several factors, such as the availability of an accurate anisotropic velocity model and adequacy of the homogeneous concept of wave propagation, as well as the choice of the frequency band. The methodology discussed here can be extended to field measurements of anisotropic attenuation needed for AVO (amplitude-variation-with-offset) analysis, amplitude-preserving migration, and seismic fracture detection.

Flow-induced alterations of ultrasonic signatures and fracture aperture under constant state of stress in a single-fractured rock

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. WA115-WA125 ◽  
Author(s):  
Arash Kamali-Asl ◽  
Bijay KC ◽  
Ehsan Ghazanfari ◽  
Ahmadreza Hedayat
Keyword(s):  
Fracture Surface ◽  
Wave Attenuation ◽  
Ultrasonic Waves ◽  
P Wave ◽  
Fracture Aperture ◽  
Frequency Content ◽  
Time Frequency ◽  
State Of Stress ◽  
Hydraulic Aperture ◽  
Constant State

Fluid-fracture surface interaction, caused by different mechanisms, is one of the underlying reasons for permeability reduction over long period of time in different georesources, such as deep geothermal systems and shale gas/oil reservoirs. The sensitivity of the ultrasonic signatures (e.g., frequency content, velocity, amplitude, and attenuation) to the changes in fracture aperture caused by fluid-fracture surface interactions can be considered as a probe for flow-induced fracture aperture evolution. Flow-through tests on an artificially fractured phyllite specimen from a geothermal reservoir along with the concurrent measurements of ultrasonic signatures of P- and cross-polarized S-waves demonstrated the sensitivity of ultrasonic signatures to the evolution of fracture aperture/permeability under a constant state of stress (i.e., constant pore and confining pressures). In particular, the closure of the fracture and the decrease of permeability led to an increase of the P-wave velocity, a decrease of the P-wave attenuation, and an increase of the S-wave amplitude. In addition, time evolution of the time-frequency maps of the transmitted ultrasonic waves revealed that partitioning of the frequency content slightly changes because the fracture aperture/permeability is altered. Specifically, alterations in hydraulic aperture are reflected in the changes of time-frequency partitioning, whereas under constant hydraulic aperture, the time-frequency partitioning is unaltered.

scholarly journals Fluid Discrimination in Ultra-Deep Reservoirs Based on a Double Double-Porosity Theory

2021 ◽  
Vol 9 ◽  
Author(s):  
Xinyang Zhou ◽  
Jing Ba ◽  
Juan E. Santos ◽  
José M. Carcione ◽  
Li-Yun Fu ◽  
...  
Keyword(s):  
Oil Recovery ◽  
Wave Attenuation ◽  
Poisson Ratio ◽  
Mass Density ◽  
Rock Physics ◽  
Spectral Ratio ◽  
Double Porosity ◽  
P Wave ◽  
Oil Saturation ◽  
Frequency Bands

We develop a methodology, based on rock-physics templates, to effectively identify reservoir fluids in ultra-deep reservoirs, where the poroelasticity model is based on the double double-porosity theory. P-wave attenuation, the ratio of the first Lamé constant to mass density (λ/ρ) and Poisson ratio are used to build the templates at the ultrasonic and seismic frequency bands to quantitatively predict the total and crack (soft) porosities and oil saturation. Attenuation on these frequency bands is estimated with the spectral-ratio and frequency-shift methods. We apply the methodology to fault-controlled karst reservoirs in the Tarim Basin (China), which contain ultra-deep hydrocarbon resources with a diverse pore-crack system, low porosity/permeability and complex oil-water spatial distributions. The results are consistent with well-log data and actual oil recovery. Crack porosity can be used as an indicator to find regions with high oil saturation, since high values implies a good pore connectivity.

scholarly journals Event couple spectral ratio <i>Q</i> method for earthquake clusters: application to northwest Bohemia

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 317-328
Author(s):  
Marius Kriegerowski ◽  
Simone Cesca ◽  
Matthias Ohrnberger ◽  
Torsten Dahm ◽  
Frank Krüger
Keyword(s):  
Wave Attenuation ◽  
Attenuation Factor ◽  
Source Region ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Earthquake Swarms ◽  
High Attenuation ◽  
Spectral Estimates ◽  
Wave Path ◽  
Spectral Ratio Method

Abstract. We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q−1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high-frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wave-field seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to northwest Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp<100. The application to S phases fails due to scattered P-phase energy interfering with S phases. The Qp anomaly supports the common hypothesis of highly fractured and fluid saturated rocks in the source region of the swarms in northwest Bohemia. However, high temperatures in a small volume around the swarms cannot be excluded to explain our observations.

Estimation of microfracture porosity in deep carbonate reservoirs based on 3D rock-physics templates

2020 ◽  
Vol 8 (4) ◽  
pp. SP43-SP52
Author(s):  
Mengqiang Pang ◽  
Jing Ba ◽  
Li-Yun Fu ◽  
José M. Carcione ◽  
Uti I. Markus ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Velocity Ratio ◽  
Rock Physics ◽  
Total Porosity ◽  
Spectral Ratio ◽  
Wave Impedance ◽  
Seismic Attenuation ◽  
Carbonate Reservoirs ◽  
P Wave ◽  
Ratio Method

Carbonate reservoirs in the S area of the Tarim Basin (China) are ultradeep hydrocarbon resources, with low porosity, complex fracture systems, and dissolved pores. Microfracturing is a key factor of reservoir connectivity and storage space. We have performed measurements on limestone samples, under different confining pressures, and we used the self-consistent approximation model and the Biot-Rayleigh theory of double porosity to study the microfractures. We have computed the fluid properties (mainly oil) as a function of temperature and pressure. Using the dependence of seismic [Formula: see text] on the microfractures, a multiscale 3D rock-physics template (RPT) is built, based on the attenuation, P-wave impedance, and phase velocity ratio. We estimate the ultrasonic and seismic attenuation with the spectral-ratio method and the improved frequency-shift method, respectively. Then, calibration of the RPTs is performed at ultrasonic and seismic frequencies. We use the RPTs to estimate the total and microfracture porosities. The results indicate that the total porosity is low and the microfracture porosity is relatively high, which is consistent with the well log data and actual oil production reports. This work presents a method for identification of deep carbonate reservoirs by using the microfracture porosity estimated from the 3D RPT, which could be exploited in oil and gas exploration.

Estimation of free gas saturation from seismic reflection surveys by the genetic algorithm inversion of a P-wave attenuation model

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. R175-R187 ◽  
Author(s):  
Eugene C. Morgan ◽  
Maarten Vanneste ◽  
Isabelle Lecomte ◽  
Laurie G. Baise ◽  
Oddvar Longva ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Seismic Reflection ◽  
Wave Attenuation ◽  
In Situ Measurements ◽  
P Wave ◽  
Ratio Method ◽  
Attenuation Model ◽  
Free Gas ◽  
Gas Saturation

Many previously proposed methods of estimating free gas saturation from seismic survey data rely on calibration to invasively collected, in situ measurements. Typically, such in situ measurements are used to parameterize or calibrate rock-physics models, which can then be applied to seismic data to achieve saturation estimates. We tested a technique for achieving estimates of the spatial distribution of gas saturation solely from shipboard seismic surveys. We estimated the quality factor from seismic reflection surveys using the spectral ratio method, and then inverted a mesoscopic-scale P-wave attenuation model to find the parameters that matched the modeled attenuation to our estimates of observed attenuation within the range of seismic frequencies. By using a genetic algorithm for this inversion, we not only searched efficiently for a global solution to the nonlinear set of equations that compose the model, but also constrain the search to a relatively broad set of realistic parameter values. Thus, our estimates do not rely on in situ measurements of these parameters, but on distributions of their possible values, many of which may be referenced from literature. We first tested this method at Blake Ridge, offshore North and South Carolina, where an approximately 400-m-deep gas-saturated zone underlies a field of methane hydrates. The extensive field work and subsequent studies at this site make it ideal for validating our method. We also demonstrated the applicability of our method to shallower deposits by presenting results from Finneidfjord, Norway, where the inversion of the P-wave attenuation model recognizes very small gas saturations.

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