Seismology of Azimuthally Anisotropic Media and Seismic Fracture Characterization

Tsvankin, Ilya; Grechka, Vladimir

doi:10.1190/1.9781560802839

Cited by 182 publications

(105 citation statements)

References 176 publications

(708 reference statements)

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“…where g ¼ b 2 a 2 and e is the crack density, which is defined as the number of cracks, N, per unit volume, V, multiplied by the average radius, r, of the penny-shaped cracks (s:t: e ¼ N V hr 3 i) (Molotkov and Bakulin 1997;Tsvankin and Grechka 2011).…”

Section: Avo Applicationsmentioning

confidence: 99%

Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin

2017

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Abstract.A new technique of amplitude versus azimuth (AVAZ) seismic inversion in horizontally transverse isotropic (HTI) media is presented. AVAZ is an effective method of characterising anisotropic variation within individual reflectors as well as characterising fractures. The compressional wave reflectivity equation in HTI media has been reformulated into a parabolic form that allows for fast and efficient inversion. The isotropic component of the azimuthal reflectivity has been separated precisely from the anisotropic component and the anisotropic component has been decoupled exactly into its constituent elliptic and anelliptic components. The exact isotropic, elliptic and anelliptic amplitude versus offset (AVO) gradient equations in HTI media are presented herein and the amount of error associated with previous approximations is also defined under the assumption of weak anisotropy. A method of calculating Thomsen's weak anisotropy parameters using these AVO gradient terms is then outlined. Compared with the elliptic method, there is reduced error incorporated in the new AVAZ method and the error relationships of this method are compared with the Fourier method.Data from an open file 3D wide azimuth seismic survey in the Surat Basin were inverted to demonstrate the effectiveness of the techniques which are presented herein. Seismic amplitudes from six azimuthal stacks were extracted over two horizons and inverted around a well where full-wave sonic and density logs were acquired. For both horizons, the error between the inverted anisotropy parameters from seismic and the inverted anisotropy parameters from wire line logs were found to be less than 5% for both horizons.

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Section: Avo Applicationsmentioning

confidence: 99%

Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin

2017

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“…The direction of polarization of the fast mode corresponds to the fracture strike and the delay between S 1 and S 2 indicate the degree of anisotropy (Yardley and Crampin 1991). These underlying seismic properties enable indirect mapping of micro-fractures whose detection and characterization offer important information needful for well path design, aiming at intersecting a larger number of permeable fractures, so sweep efficiency and hydrocarbon recovery are improved (Finkbeiner et al 1997;Bates et al 1999;Tsvankin and Grechka 2011).…”

Section: Introductionmentioning

confidence: 99%

“…Crampin (1984) established that most geologic formations possess a certain degree of anisotropy which can be classified into different symmetry classes based on the structure of their elastic stiffness tensors and the number of independent components of the tensors (Thomsen 1986;Tsvankin 2001;Tsvankin and Grechka 2011). Horizontal layering in sedimentary rocks has been described to generate layer anisotropy known as vertical transverse isotropy (VTI) (Hornby et al 1994) while aligned vertical cracks would induce horizontal transverse isotropy (HTI) (Tsvankin and Grechka 2011). The occurrence of set (s) of stressinduced aligned vertical micro cracks within horizontal layered sedimentary formations would combine layer-induced VTI and fracture-imposed HTI to generate orthorhombic anisotropy (Fig.…”

Section: Introductionmentioning

confidence: 99%

Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA

Osinowo

Chapman

Bell

et al. 2017

Pure Appl. Geophys.

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Abstract-In this study we present a step-by-step theoretical modelling approach, using established seismic wave propagation theories in anisotropic media, to generate unique anisotropic reflection patterns observed from three-dimensional pure-mode pressure (3D-PP), full-azimuth and full-offset seismic reflection data acquired over a naturally fractured tight carbonate field, onshore Texas, USA. Our aim is to gain an insight into the internal structures of the carbonate reservoir responsible for the observed anisotropic reflection patterns. From the generated model we were able to establish that the observed field seismic reflection patterns indicate azimuthal anisotropy in the form of crack induced shearwave splitting and variation in P-wave velocity with offset and azimuth. Amplitude variation with azimuth (AVAZ) analysis also confirmed multi-crack sets induced anisotropy which is characteristic of orthorhombic symmetry, evident as multiple bright and dim-amplitude azimuth directions as well as complete reversal of bright-amplitude to dim-amplitude azimuth direction as the angle of incidence increases from near (B15°) to mid (C30°) offsets. Finally, we fitted the generated P-wave velocity into an ellipse to determine the intensity and orientation (N26E) of the open crack set as well as the direction of the minimum in situ stress axis (N116E) within the reservoir. The derived information served as an aid for the design of horizontal well paths that would intercept open fractures and ensure production optimization of the carbonate reservoir, which was on production decline despite reservoir studies that indicate un-depleted reserves.

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“…They show how to estimate physical properties such as the normal and tangential compliances of the fractures from multicomponent data. The compliances can then be used to infer fracture density and infill, as also discussed by Tsvankin and Grechka (2011). However, existing methods of fracture detection are mostly based on reflection traveltimes and/or amplitudes (AVO analysis).…”

Section: Introductionmentioning

confidence: 99%

High-resolution Fracture Characterization Using Elastic Full-waveform Inversion

Zhang¹,

Tsvankin²,

Alkhalifah³

2017

Proceedings

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SummaryCurrent methodologies to characterize fractures at the reservoir scale have serious limitations in spatial resolution. Here, we propose to estimate both the spatial distribution and physical properties of fractures using full waveform inversion (FWI) of multicomponent surface seismic data. An effective orthorhombic medium with five clusters of vertical fractures distributed in a checkboard fashion is used to test the algorithm. To better understand the inversion results, we analyze the FWI radiation patterns of the fracture weaknesses. A shape regularization term is added to the objective function to improve the inversion for the horizontal weakness, which is otherwise poorly constrained. Alternatively, a simplified model of penny-shaped cracks is used to reduce the nonuniqueness in the inverted weaknesses and achieve a faster convergence.

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Seismology of Azimuthally Anisotropic Media and Seismic Fracture Characterization

Cited by 182 publications

References 176 publications

Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin

Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin

Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA

High-resolution Fracture Characterization Using Elastic Full-waveform Inversion

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