Seismic attenuation of Atlantic margin basalts: Observations and modeling

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. B211-B221 ◽  
Author(s):  
Jennifer Maresh ◽  
Robert S. White ◽  
Richard W. Hobbs ◽  
John R. Smallwood
Keyword(s):  
Seismic Energy ◽  
Seismic Signal ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Thin Layers ◽  
Seismic Survey ◽  
Rock Properties ◽  
Intrinsic Attenuation ◽  
High Impedance ◽  
1D Modeling

Paleogene basalts are present over much of the northeastern Atlantic European margin. In regions containing significant thicknesses of layered basalt flows, conducting seismic imaging within and beneath the volcanic section has proven difficult, largely because the basalts severely attenuate and scatter seismic energy. We use data from a vertical seismic profile (VSP) from well 164/07-1 that penetrated [Formula: see text] of basalt in the northern Rockall Trough west of Britain to measure the seismic attenuation caused by the in-situ basalts. The effective quality factor [Formula: see text] of the basalt layer is found from the VSP to be 15–35, which is considerably lower (more attenuative) than the intrinsic attenuation measured on basalt samples in the laboratory. We then run synthetic seismogram models to investigate the likely cause of the attenuation. Full waveform 1D modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the VSP can be accounted for by the scattering effects of multiple thin layers with high impedance contrasts. Phase-screen seismic modeling of the rugose basalt surface at the top-of-basalt sediment interface, with the magnitude and wavelength of the relief constrained by a 3D seismic survey around the well, suggests that surface scattering from this interface plays a much smaller role than internal scattering in attenuating the seismic signal as it passes through the basalt sequence.

Seismic attenuation attributes with applications on conventional and unconventional reservoirs

2016 ◽  
Vol 4 (1) ◽  
pp. SB63-SB77 ◽  
Author(s):  
Fangyu Li ◽  
Sumit Verma ◽  
Huailai Zhou ◽  
Tao Zhao ◽  
Kurt J. Marfurt
Keyword(s):  
Reservoir Characterization ◽  
Seismic Energy ◽  
Seismic Attenuation ◽  
Thin Layers ◽  
Estimation Model ◽  
Fort Worth Basin ◽  
Intrinsic Attenuation ◽  
Spectral Attenuation ◽  
Apparent Attenuation ◽  
Attenuation Estimation

Seismic attenuation, generally related to the presence of hydrocarbon accumulation, fluid-saturated fractures, and rugosity, is extremely useful for reservoir characterization. The classic constant attenuation estimation model, focusing on intrinsic attenuation, detects the seismic energy loss because of the presence of hydrocarbons, but it works poorly when spectral anomalies exist, due to rugosity, fractures, thin layers, and so on. Instead of trying to adjust the constant attenuation model to such phenomena, we have evaluated a suite of seismic spectral attenuation attributes to quantify the apparent attenuation responses. We have applied these attributes to a conventional and an unconventional reservoir, and we found that those seismic attenuation attributes were effective and robust for seismic interpretation. Specifically, the spectral bandwidth attribute correlated with the production of a gas sand in the Anadarko Basin, whereas the spectral slope of high frequencies attribute correlated with the production in the Barnett Shale of the Fort Worth Basin.

Attenuation study of a clay-rich dense zone in fractured carbonate reservoirs

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. B205-B216
Author(s):  
Fateh Bouchaala ◽  
Mohammed Y. Ali ◽  
Jun Matsushima
Keyword(s):  
United Arab Emirates ◽  
Soft Clay ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Carbonate Reservoirs ◽  
Intrinsic Attenuation ◽  
Flow Mechanisms ◽  
Order Of Magnitude ◽  
Attenuation Mechanism ◽  
Dense Zone

Seismic attenuation in clay-rich dense zones remains unknown, despite the importance of such zones in hydrocarbon reservoirs, where they delimit the reservoir zones and isolate them from nearby aquifers. We have determined that a dense zone separating two carbonate reservoirs of an onshore oilfield in Abu Dhabi, United Arab Emirates, exhibits the highest intrinsic attenuation even though the zone contains no hydrocarbons. The frictional movement due to the elastic contrast between the hard carbonates and soft clay is most likely the dominant mechanism in the dense zone. The compressional sonic and vertical seismic profile (VSP) attenuation are on the same order of magnitude and are both maximum in the dense zone. Therefore, it is possible that the same attenuation mechanism in this zone exists at low and high frequencies; whereas the intrinsic attenuation mechanism in the reservoir zones, which are more permeable and porous than the dense zone, can be explained by the coexistence of global and squirt-flow mechanisms. Moreover, sonic attenuation exhibits higher magnitudes than VSP attenuation in these zones. This is due to the fact that the squirt-flow mechanism, which can take place between pores and fractures, is more important at sonic frequencies. The scattering mechanism is also important in the reservoir zones; this is due to the high heterogeneity and the presence of fractures in these zones.

Robust prestack Q-determination using surface seismic data: Part 1 — Method and synthetic examples

Geophysics ◽  
2012 ◽  
Vol 77 (1) ◽  
pp. R45-R56 ◽  
Author(s):  
Carl Reine ◽  
Roger Clark ◽  
Mirko van der Baan
Keyword(s):  
Reservoir Characterization ◽  
Accurate Determination ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Spectral Interference ◽  
Seismic Survey ◽  
Time Frequency ◽  
Frequency Independent ◽  
Variable Window ◽  
Amplitude Variation With Angle

The accurate determination of seismic attenuation, or [Formula: see text], is useful for signal enhancement and reservoir characterization. To arrive at the necessary accuracy however, a number of issues must be addressed in the measurement technique. Specifically, spectral interference from closely spaced reflections is a major concern, in addition to the assumptions and errors associated with the raypath geometries of the reference and measured reflections. We have developed a robust method for measuring attenuation from prestack surface seismic gathers that helps minimize these issues. In our prestack [Formula: see text]-inversion technique; the presence of spectral interference was first reduced by making use of a variable-window time-frequency transform. To minimize the effects of the remaining interference, we then made use of an inversion scheme operating simultaneously in the frequency and traveltime-difference coordinates. A by-product of this inversion was a collection of the frequency-independent amplitude changes, which in the absence of geometric spreading, contains valuable amplitude variation with angle information, free from attenuation amplitude losses. Furthermore, under the assumption of locally 1D velocity and attenuation distributions, we made use of the [Formula: see text] transform to operate on traces of constant horizontal slowness. This allowed angle-dependent effects in the overburden such as attenuation anisotropy and source or receiver directivity to be eliminated. In the second part of our study, published separately, this technique was also demonstrated upon a shallow 3D seismic survey, and the measurements compared to another Q-estimation technique, as well as measurements from a vertical seismic profile.

Seismic attenuation tomography using the frequency shift method

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 895-905 ◽  
Author(s):  
Youli Quan ◽  
Jerry M. Harris
Keyword(s):  
Frequency Shift ◽  
Low Frequency ◽  
Seismic Signal ◽  
Seismic Attenuation ◽  
Seismic Survey ◽  
Shift Method ◽  
Geometric Spreading ◽  
Frequency Independent ◽  
Q Model ◽  
Frequency Components

We present a method for estimating seismic attenuation based on frequency shift data. In most natural materials, seismic attenuation increases with frequency. The high‐frequency components of the seismic signal are attenuated more rapidly than the low‐frequency components as waves propagate. As a result, the centroid of the signal's spectrum experiences a downshift during propagation. Under the assumption of a frequency‐independent Q model, this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically. The frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In comparison to some other methods of estimating attenuation, our frequency shift method is relatively insensitive to geometric spreading, reflection and transmission effects, source and receiver coupling and radiation patterns, and instrument responses. Tests of crosswell attenuation tomography on 1-D and 2-D geological structures are presented.

Structural interpretation using refraction velocities from marine seismic surveys

Geophysics ◽  
1986 ◽  
Vol 51 (1) ◽  
pp. 12-19 ◽  
Author(s):  
James F. Mitchell ◽  
Richard J. Bolander
Keyword(s):  
Sedimentary Rock ◽  
Seismic Energy ◽  
Seismic Survey ◽  
Subsurface Structure ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Wide Range ◽  
Streamer Length ◽  
Set Up

Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.

P- and S-wave attenuation logs from monopole sonic data

Geophysics ◽  
2000 ◽  
Vol 65 (3) ◽  
pp. 755-765 ◽  
Author(s):  
Xinhua Sun ◽  
Xiaoming Tang ◽  
C. H. (Arthur) Cheng ◽  
L. Neil Frazer
Keyword(s):  
Wave Attenuation ◽  
Fluid Velocity ◽  
P Wave ◽  
Reservoir Rock ◽  
Rock Properties ◽  
S Wave ◽  
Intrinsic Attenuation ◽  
Modified Method ◽  
Receiver Array ◽  
Attenuation Profiles

In this paper, a modification of an existing method for estimating relative P-wave attenuation is proposed. By generating synthetic waveforms without attenuation, the variation of geometrical spreading related to changes in formation properties with depth can be accounted for. With the modified method, reliable P- and S-wave attenuation logs can be extracted from monopole array acoustic waveform log data. Synthetic tests show that the P- and S-wave attenuation values estimated from synthetic waveforms agree well with their respective model values. In‐situ P- and S-wave attenuation profiles provide valuable information about reservoir rock properties. Field data processing results show that this method gives robust estimates of intrinsic attenuation. The attenuation profiles calculated independently from each waveform of an eight‐receiver array are consistent with one another. In fast formations where S-wave velocity exceeds the borehole fluid velocity, both P-wave attenuation ([Formula: see text]) and S-wave attenuation ([Formula: see text]) profiles can be obtained. P- and S-wave attenuation profiles and their comparisons are presented for three reservoirs. Their correlations with formation lithology, permeability, and fractures are also presented.

Q estimation from vertical seismic profile data and anomalous variations in the central North Sea

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 615-626 ◽  
Author(s):  
S. D. Stainsby ◽  
M. H. Worthington
Keyword(s):  
North Sea ◽  
Pulse Width ◽  
Spectral Ratio ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Recording Equipment ◽  
Vertical Seismic Profile ◽  
High Attenuation ◽  
Vsp Data ◽  
Central North Sea

Four different methods of estimating Q from vertical seismic profile (VSP) data based on measurements of spectral ratios, pulse amplitude, pulse width, and zeroth lag autocorrelation of the attenuated impulse are described. The last procedure is referred to as the pulse‐power method. Practical problems concerning nonlinearity in the estimating procedures, uncertainties in the gain setting of the recording equipment, and the influence of structure are considered in detail. VSP data recorded in a well in the central North Sea were processed to obtain estimates of seismic attenuation. These data revealed a zone of high attenuation from approximately 4 900 ft to [Formula: see text] ft with a value of [Formula: see text] Results of the spectral‐ratio analysis show that the data conform to a linear constant Q model. In addition, since the pulse‐width measurement is dependent upon the dispersive model adopted, it is shown that a nondispersive model cannot possibly provide a match to the real data. No unambiguous evidence is presented that explains the cause of this low Q zone. However, it is tentatively concluded that the seismic attenuation may be associated with the degree of compaction of the sediments and the presence of deabsorbed gases.

scholarly journals Interface-targeted seismic velocity estimation using machine learning

2019 ◽  
Vol 218 (1) ◽  
pp. 45-56 ◽  
Author(s):  
C Nur Schuba ◽  
Jonathan P Schuba ◽  
Gary G Gray ◽  
Richard G Davy
Keyword(s):  
Neural Network ◽  
Regression Model ◽  
Dimensional Space ◽  
Seismic Profile ◽  
Velocity Estimation ◽  
Seismic Survey ◽  
Wide Angle ◽  
Seismic Velocities ◽  
Lower Dimensional Space ◽  
Lower Dimensional

SUMMARY We present a new approach to estimate 3-D seismic velocities along a target interface. This approach uses an artificial neural network trained with user-supplied geological and geophysical input features derived from both a 3-D seismic reflection volume and a 2-D wide-angle seismic profile that were acquired from the Galicia margin, offshore Spain. The S-reflector detachment fault was selected as the interface of interest. The neural network in the form of a multilayer perceptron was employed with an autoencoder and a regression layer. The autoencoder was trained using a set of input features from the 3-D reflection volume. This set of features included the reflection amplitude and instantaneous frequency at the interface of interest, time-thicknesses of overlying major layers and ratios of major layer time-thicknesses to the total time-depth of the interface. The regression model was trained to estimate the seismic velocities of the crystalline basement and mantle from these features. The ‘true’ velocities were obtained from an independent full-waveform inversion along a 2-D wide-angle seismic profile, contained within the 3-D data set. The autoencoder compressed the vector of inputs into a lower dimensional space, then the regression layer was trained in the lower dimensional space to estimate velocities above and below the targeted interface. This model was trained on 50 networks with different initializations. A total of 37 networks reached minimum achievable error of 2 per cent. The low standard deviation (<300  m s−1) between different networks and low errors on velocity estimations demonstrate that the input features were sufficient to capture variations in the velocity above and below the targeted S-reflector. This regression model was then applied to the 3-D reflection volume where velocities were predicted over an area of ∼400 km2. This approach provides an alternative way to obtain velocities across a 3-D seismic survey from a deep non-reflective lithology (e.g. upper mantle) , where conventional reflection velocity estimations can be unreliable.

Reflection and transmission responses of a layered isotropic viscoelastic medium

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 307-323 ◽  
Author(s):  
Bjørn Ursin ◽  
Alexey Stovas
Keyword(s):  
Recursive Algorithm ◽  
Thin Layers ◽  
Reflection And Transmission ◽  
S Waves ◽  
First Order ◽  
Transmission Coefficients ◽  
Intrinsic Attenuation ◽  
Amplitude Versus Offset ◽  
Symmetry Relations ◽  
Seismic Wavefield

Transmission effects in the overburden are important for amplitude versus offset (AVO) studies and for true‐amplitude imaging of seismic data. Thin layers produce transmission effects which depend on frequency and slowness. We consider an inhomogeneous viscoelastic layered isotropic medium where the parameters depend on depth only. This takes into account both the effects of intrinsic attenuation and the effects of the layering (including changes in attenuation). The seismic wavefield is decomposed into up‐ and downgoing waves scaled with respect to the vertical energy flux. This gives important symmetry relations for the reflection and transmission responses. For a stack of homogeneous layers, the exact reflection response can be computed in a numerically stable way by a simple layer‐recursive algorithm. The reflection and transmission coefficients at a plane interface are functions of the complex medium parameters (depending on frequency) and the real horizontal slowness parameter. Approximations for weak contrast and weak attenuation are derived and compared to the exact values in two numerical examples. We derive first‐order approximations of the PP and SS transmission responses which are direct extensions of the well‐known O'Doherty‐Anstey formula. They consist of a phase shift and attenuation term from direct transmission through the layers and two attenuation terms from backscattered P‐ and S‐waves. The average of these transmission responses may be used for overburden corrections in AVO analysis. The first‐order PP and PS reflection responses have been computed for a stack of very thin layers corresponding to about 2800 m thickness. Because of a lack of data, the intrinsic attenuation was assumed to be constant in the layers. In the seismic frequency band, the intrinsic attenuation dominates the thin‐layer effects. Approximate and exact layer‐recursive modeling of the reflection responses for this layered medium are in good agreement.

PRACTICAL USE OF BOREHOLE SEISMIC IN EXPLORATION

1984 ◽  
Vol 24 (1) ◽  
pp. 429
Author(s):  
F. Sandnes W. L. Nutt ◽  
S. G. Henry
Keyword(s):  
Seismic Data ◽  
Seismic Profile ◽  
Seismic Survey ◽  
Vertical Seismic Profile ◽  
Direct Signal ◽  
Seismic Fault ◽  
Time Calibration ◽  
Vsp Data ◽  
Borehole Seismic ◽  
Processing Techniques

The improvement of acquisition and processing techniques has made it possible to study seismic wavetrains in boreholes.With careful acquisition procedures and quantitative data processing, one can extract useful information on the propagation of seismic events through the earth, on generation of multiples and on the different reflections coming from horizons that may not all be accessible by surface seismic.An extensive borehole seismic survey was conducted in a well in Conoco's contract area 'Block B' in the South China Sea. Shots at 96 levels were recorded, and the resulting Vertical Seismic Profile (VSP) was carefully processed and analyzed together with the Synthetic Seismogram (Geogram*) and the Synthetic Vertical Seismic Profile (Synthetic VSP).In addition to the general interpretation of the VSP data, i.e. time calibration of surface seismic, fault identification, VSP trace inversion and VSP Direct Signal Analysis, the practical inclusion of VSP data in the reprocessing of surface seismic data was studied. Conclusions that can be drawn are that deconvolution of surface seismic data using VSP data must be carefully approached and that VSP can be successfully used to examine phase relationships in seismic data.

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