An experimental investigation of factors influencing compressional‐ and shear‐wave velocities and attenuations in tight gas sandstones

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Azra N. Tutuncu ◽  
Augusto L. Podio ◽  
Mukul M. Sharma
Keyword(s):  
Shear Wave ◽  
Correlation Method ◽  
Clay Content ◽  
Spectral Ratio ◽  
Peak Frequency ◽  
Ratio Method ◽  
Tight Gas ◽  
S Waves ◽  
Amplitude Spectra ◽  
Tight Gas Sandstones

Results are presented for compressional and shear velocities and attenuations in fully brine‐saturated tight gas cores with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. The influence of porosity, clay content, frequency, and stress on velocities and attenuations were examined using the amplitude spectra of P‐ and S‐waves in the frequency domain. Attenuations of samples were obtained using the spectral ratio method. For a few selected samples the attenuations were also measured using the length correlation method and these results were compared with the spectral ratio results. In tight gas sandstones, the attenuations obtained were 2 to 5 times greater than the attenuation obtained for Berea sandstone. In general, the presence of clay softens the rock grain contacts causing smaller values of compressional ([Formula: see text] and shear ([Formula: see text]) velocities as the clay content increases. However, the [Formula: see text] ratio was found to increase with clay content. Compressional‐and shear‐wave amplitude spectra exhibited a shift in peak frequency toward lower frequencies for samples with higher clay content when compared to clean samples. Velocities and attenuations were found to be frequency dependent, but the positive slope of both compressional and shear attenuations indicate that scattering starts to dominate at the lower frequency end of the ultrasonic measurements. Both [Formula: see text] and [Formula: see text] increased while both compressional and shear attenuations decreased when stress was increased.

scholarly journals Finite element model calibration of multi-story buildings through interferometric imaging and spectral ratio method

2016 ◽  
Vol 43 (4) ◽  
pp. 320-325 ◽  
Author(s):  
Yavuz Kaya
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Spectral Ratio ◽  
Element Model ◽  
Ratio Method ◽  
Interferometric Imaging ◽  
Simplified Approach ◽  
Amplitude Spectra ◽  
Finite Element Model Calibration ◽  
Sr Method

To identify and calibrate the finite element model for multi-story buildings, a simplifıed approach is being introduced in this paper; this methodology is based on interferometric imaging and encompasses spectral ratio (SR) method. Interferometric imaging provides a new set of seismic data free of coupling between structures to its subsurface and independent of the excitation of the building. The SR method, on the other hand, is the ratio of Fourier amplitude spectra of the roof-deconvolved records on two adjacent stories. The newly introduced methodology enables each story to be identified uniquely for its stiffness since the SR of a particular story is dependent only on the properties of itself and the stories above.

Integrated estimation of interval-attenuation profiles

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. A19-A23 ◽  
Author(s):  
James Rickett
Keyword(s):  
Reservoir Characterization ◽  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Ratio Method ◽  
Amplitude Analysis ◽  
Linear Inversion ◽  
Amplitude Spectra ◽  
Initial Spectrum ◽  
Spectral Ratio Method ◽  
Attenuation Profiles

Quantitative estimates of seismic attenuation are useful for a variety of applications, ranging from seismic-acquisition design, to seismic processing, amplitude analysis, and reservoir characterization. I frame the estimation of interval attenuation from a set of seismic wavelets as a linear inversion of their log-amplitude spectra. The initial spectrum at the first depth location and a set of depth-varying amplitude scalers are estimated simultaneously with an effective-attenuation [Formula: see text] profile. The algorithm can be regarded as a tomographic extension of the spectral-ratio method that uses all the information available in the amplitude spectra, appropriately weighted so that estimates are not biased by noise. Constraints can be applied to ensure the [Formula: see text] values vary smoothly, and solving for log [Formula: see text] rather than [Formula: see text] ensures only positive attenuation values. Tests on synthetic and field data illustrate the trade-off between vertical resolution and sensitivity to noise. A covariance study indicates that improvements in interval-attenuation estimates over the traditional spectral-ratio method come from systematic-noise handling and the explicit constraints on [Formula: see text], rather than the fact that the inversion ties the log-spectral data together with a single estimate of the spectrum at the first depth location.

Estimation of shear-wave interval attenuation from mode-converted data

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. D11-D19 ◽  
Author(s):  
Bharath Shekar ◽  
Ilya Tsvankin
Keyword(s):  
Shear Wave ◽  
Attenuation Coefficient ◽  
Reservoir Characterization ◽  
Wave Attenuation ◽  
Pure Shear ◽  
Synthetic Data ◽  
Spectral Ratio ◽  
Ratio Method ◽  
S Wave ◽  
Target Layer

Interval attenuation measurements provide valuable information for reservoir characterization and lithology discrimination. We extend the attenuation layer-stripping method of Behura and Tsvankin to mode-converted (PS) waves with the goal of estimating the S-wave interval attenuation coefficient. By identifying PP and PS events with shared ray segments and applying the [Formula: see text] method, we first perform kinematic construction of pure shear (SS) events in the target layer and overburden. Then, the modified spectral-ratio method is used to compute the effective shear-wave attenuation coefficient for the target reflection. Finally, application of the dynamic version of velocity-independent layer stripping to the constructed SS reflections yields the interval S-wave attenuation coefficient in the target layer. The attenuation coefficient estimated for a range of source-receiver offsets can be inverted for the interval attenuation parameters. The method is tested on multicomponent synthetic data generated with the anisotropic reflectivity method for layered VTI (transversely isotropic with a vertical symmetry axis) and orthorhombic media.

Estimation of porosity and fluid saturation in carbonates from rock-physics templates based on seismic Q

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. M25-M36 ◽  
Author(s):  
Mengqiang Pang ◽  
Jing Ba ◽  
José M. Carcione ◽  
Stefano Picotti ◽  
Jian Zhou ◽  
...  
Keyword(s):  
Seismic Data ◽  
Rock Physics ◽  
Clay Content ◽  
Spectral Ratio ◽  
Gas Production ◽  
Ratio Method ◽  
Well Log ◽  
Reservoir Properties ◽  
Seismic Properties ◽  
Fluid Saturation

Rock-physics templates establish a link between seismic properties (e.g., velocity, density, impedance, and attenuation) and reservoir properties such as porosity, fluid saturation, permeability, and clay content. We focus on templates based on attenuation (seismic [Formula: see text] or quality factor), which are highly affected by those properties, and we consider carbonate reservoirs that constitute 60% of the world oil reserves and a potential for additional gas reserves. The seismic properties are described with mesoscopic-loss models, such as the White model of patchy saturation and the double double-porosity model, which include frame and fluid heterogeneities. We have performed ultrasonic experiments, and we estimate the attenuation of the samples and the reservoir by using the spectral ratio method and the improved frequency-shift method. Then, multiscale calibrations of the templates are performed by using laboratory, well log, and seismic data. On this basis, reservoir porosity and fluid saturation are quantitatively evaluated. We first apply the templates to ultrasonic data of limestone using the White model. Then, we consider seismic data of a carbonate gas reservoir of MX work area in the Sichuan Basin, southwest China. A survey line in the area is selected to detect the reservoir by using the templates. The results indicate that the estimated porosity and saturation are consistent with well-log data and actual gas production results. The methodology indicates that the microstructural characteristics of a high-quality reservoir can effectively be predicted using seismic [Formula: see text].

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