Estimating attenuation and the relative information content of amplitude and phase spectra

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. R19-R27 ◽  
Author(s):  
James Rickett
Keyword(s):  
Phase Difference ◽  
Seismic Waves ◽  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Ratio Method ◽  
Relative Uncertainty ◽  
Phase Information ◽  
Relative Information ◽  
The Difference ◽  
Phase Spectra

Seismic attenuation affects both the amplitude and phase of seismic waves. Algorithms to estimate attenuation are split among those that use amplitude information (e.g., spectral-ratio method), those that use phase information (e.g., rise-time method), and those that use a combination of both (e.g., time-domain algorithms). In this study, I explore the relative information provided by amplitude and phase spectra. To do this, I show how the difference in phase spectra between waveforms recorded at two depth levels can be used to estimate attenuation. This phase-difference method is analogous to the method of spectral ratios, but uses phase information rather than amplitude information. Under the simplifying assumption that the noise in both log-amplitude and phase spectra can be modeled as uncorrelated Gaussian random variables with equal variance, the posterior variances in the attenuation estimates from the spectral-ratio and phase-difference methods can be compared directly. It turns out that over typical seismic bandwidths and typical levels of attenuation, the relative uncertainty in estimates of attenuation from phase spectra is approximately twice the relative uncertainty in estimates of attenuation from log-amplitude spectra. Including phase and amplitude information simultaneously (as opposed to just amplitude information) reduces the relative uncertainty by only about 10% over seismic bandwidths. This reduction in uncertainty is not large, but may be significant depending on the sensitivity of the application.

Accurate interval Q-factor estimation from VSP data

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. WA149-WA156 ◽  
Author(s):  
E. Blias
Keyword(s):  
Real Data ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Seismic Quality Factor ◽  
Vsp Data ◽  
Considerable Impact ◽  
The Difference ◽  
Factor Estimation

Inelastic attenuation, quantified by [Formula: see text], the seismic quality factor, has considerable impact on surface seismic reflection data. A new method for interval [Formula: see text]-factor estimation using near-offset VSP data was based on an objective function minimization measuring the difference between cumulative [Formula: see text] estimates and those calculated through interval [Formula: see text]. To calculate interval [Formula: see text], we used all receiver pairs that provided reasonable [Formula: see text] values. To estimate [Formula: see text] between two receiver levels, we used the equation that links amplitudes at different levels and could provide more accurate [Formula: see text] values than the spectral-ratio method. To improve interval [Formula: see text] estimates, which rely on traveltimes, we used a high-accuracy approach in the frequency domain to determine time shifts. Application of this method to real data demonstrated reasonable correspondence between [Formula: see text] estimates and log data.

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.

scholarly journals Spectral-ratio tomography for seismic attenuation estimation

2021 ◽  
Vol 18 (3) ◽  
pp. 392-405
Author(s):  
Ziqi Jin ◽  
Ying Shi ◽  
Qiqi Ma ◽  
Deguang Tian ◽  
Qi'an Meng ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Estimation Method ◽  
Synthetic Data ◽  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Estimation Methods ◽  
Inversion Method ◽  
Target Layer ◽  
Reservoir Parameter ◽  
Attenuation Estimation

Abstract When measuring surface seismic data, an accurate attenuation estimation method is necessary to compensate for the energy loss and phase distortion of seismic waves, and is also beneficial for further quantitative amplitude analyses and reservoir parameter predictions. For conventional Q-estimation methods (such as the log spectral-ratio (LSR) method and attenuated traveltime tomography), accuracy may be affected by the differences between the overburden ray paths of two selected reflections (we call it the overburden effect). In this study, we design a more accurate Q-tomography method to estimate Q-values (both in the overburden and target layer simultaneously) without overburden assumptions. We address the overburden effect by using an inversion method, which allows us to separate attenuation effects from the overburden through the traveltime differences in the tomography grid cells. We test the method on synthetic data and prove its feasibility and effectiveness by applying it to field data.

A Study on Characteristics of Seismic Attenuation by Using Spectral Ratio Method

2014 ◽  
Vol 51 (5) ◽  
pp. 687-695 ◽  
Author(s):  
Jin-woo Lee ◽  
Ji-ho Ha ◽  
Hwi-Kyung Ko ◽  
Woo-Keen Chung ◽  
Sung-ryul Shin
Keyword(s):  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Ratio Method ◽  
Spectral Ratio Method

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.

scholarly journals Double-difference seismic attenuation tomography method and its application to The Geysers geothermal field, California

2021 ◽  
Vol 225 (2) ◽  
pp. 926-949
Author(s):  
Hao Guo ◽  
Clifford Thurber
Keyword(s):  
Spectral Ratio ◽  
Geothermal Field ◽  
Seismic Attenuation ◽  
Double Difference ◽  
Ratio Method ◽  
Moderate Degree ◽  
Attenuation Structure ◽  
The Geysers ◽  
Spectral Ratio Method ◽  
Tomography Method

SUMMARY Knowledge of attenuation structure is important for understanding subsurface material properties. We have developed a double-difference seismic attenuation (DDQ) tomography method for high-resolution imaging of 3-D attenuation structure. Our method includes two main elements, the inversion of event-pair differential ${t^*}$ ($d{t^*}$) data and 3-D attenuation tomography with the $d{t^*}$ data. We developed a new spectral ratio method that jointly inverts spectral ratio data from pairs of events observed at a common set of stations to determine the $d{t^*}$ data. The spectral ratio method cancels out instrument and site response terms, resulting in more accurate $d{t^*}$ data compared to absolute ${t^*}$ from traditional methods using individual spectra. Synthetic tests show that the inversion of $d{t^*}$ data using our spectral ratio method is robust to the choice of source model and a moderate degree of noise. We modified an existing velocity tomography code so that it can invert $d{t^*}$ data for 3-D attenuation structure. We applied the new method to The Geyser geothermal field, California, which has vapour-dominated reservoirs and a long history of water injection. A new Qp model at The Geysers is determined using P-wave data of earthquakes in 2011, using our updated earthquake locations and Vp model. By taking advantage of more accurate $d{t^*}$ data and the cancellation of model uncertainties along the common paths outside of the source region, the DDQ tomography method achieves higher resolution, especially in the earthquake source regions, compared to the standard tomography method using ${t^*}$ data. This is validated by both the real and synthetic data tests. Our Qp and Vp models show consistent variations in a normal temperature reservoir that can be explained by variations in fracturing, permeability and fluid saturation and/or steam pressure. A prominent low-Qp and Vp zone associated with very active seismicity is imaged within a high temperature reservoir at depths below 2 km. This anomalous zone is likely partially saturated with injected fluids.

Seismic Attenuation Estimation Using an Enhanced Log Spectral Ratio Method

2022 ◽  
pp. 1-1
Author(s):  
Naihao Liu ◽  
Shengtao Wei ◽  
Yang Yang ◽  
Shengjun Li ◽  
Fengyuan Sun ◽  
...  
Keyword(s):  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Ratio Method ◽  
Spectral Ratio Method ◽  
Attenuation Estimation

Seismic attenuation estimation using the modified log spectral ratio method

2018 ◽  
Vol 159 ◽  
pp. 386-394 ◽  
Author(s):  
Naihao Liu ◽  
Bo Zhang ◽  
Jinghuai Gao ◽  
Zhaoqi Gao ◽  
Shengjun Li
Keyword(s):  
Spectral Ratio ◽  
Seismic Attenuation ◽  
Ratio Method ◽  
Spectral Ratio Method ◽  
Attenuation Estimation
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