PP azimuthal‐amplitudes and ‐acoustic impedance for fractured carbonate reservoir characterization

Lynn, Heloise B.; Narhari, Srinivasa Rao; Al-Ashwak, Samar; Kidambi, Vijaya Kumar; Al-Qadeeri, Bashar; Al-Khaled, Osman

doi:10.1190/1.3513378

Cited by 5 publications

(4 citation statements)

References 6 publications

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“…Traditional seismic methods for fracture characterization retrieve fracture information by analyzing reflection P-wave amplitude variation with offset and azimuth (AVOAz) (Rüger, 1998;Shen et al, 2002;Hall and Kendall, 2003;Shaw and Sen, 2006;Liu et al, 2010;Lynn et al, 2010) or by studying S-wave splitting Van Dok et al, 2001;Angerer et al, 2002;Crampin and Chastin, 2003;Vetri et al, 2003). Both methods view fractured reservoirs as an equivalent anisotropic medium based on the assumptions that fractures are spatially dense and that their spacing is much smaller than a seismic wavelength.…”

Section: Introductionmentioning

confidence: 99%

Fracture clustering effect on amplitude variation with offset and azimuth analyses

2017

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Traditional amplitude variation with offset and azimuth (AVOAz) analysis for fracture characterization extracts fracture properties through analysis of reflection AVOAz to determine anisotropic parameters (e.g., Thomsen's parameters) that are then related to fracture properties. The validity of this method relies on the basic assumption that a fractured unit can be viewed as an equivalent anisotropic medium. As a rule of thumb, this assumption is taken to be valid when the fracture spacing is less than λ∕10. Under the effective medium assumption, diffractions from individual fractures destructively interfere and only specular reflections from boundaries of a fractured layer can be observed in seismic data. The effective medium theory has been widely used in fracture characterization, and its applicability has been validated through many field applications. However, through numerical simulations, we find that diffractions from fracture clusters can significantly distort the AVOAz signatures when a fracture system has irregular spacing even though the average fracture spacing is much smaller than a wavelength (e.g., ≪ λ∕10). Contamination by diffractions from irregularly spaced fractures on reflections can substantially bias the fracture properties estimated from AVOAz analysis and may possibly lead to incorrect estimates of fracture properties. Additionally, through Monte Carlo simulations, we find that fracture spacing uncertainty inverted from amplitude variation with offset (AVO) analysis can be up to 10%-20% when fractures are not uniformly distributed, which should be the realistic state of fractures present in the earth. Also, AVOAz and AVO analysis gives more reliable estimates of fracture properties when reflections at the top of the fractured layer are used compared with those from the bottom of the layer.

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Section: Introductionmentioning

confidence: 99%

Fracture clustering effect on amplitude variation with offset and azimuth analyses

2017

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“…Traditional seismic methods for fracture characterization include shear wave birefringence Dok et al, 2001;Angerer et al, 2002;Vetri et al, 2003) and amplitude variations with offset and azimuth (AVOA) (Ruger, 1998;Shen et al, 2002;Hall et al, 2003;Liu et al, 2010;Lynn et al, 2010). These methods are based on the equivalent medium theory with the assumption that fracture dimension and spacing are small relative to the seismic wave length, so a fracture zone behaves like an equivalent anisotropic medium.…”

Section: Discussionmentioning

confidence: 99%

Reservoir fracture characterizations from seismic scattered waves

Fang¹,

Fehler²,

Zhu³

et al. 2012

SEG Technical Program Expanded Abstracts 2012

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SUMMARYThe measurements of fracture parameters, such as fracture orientation, fracture density and fracture compliance, in a reservoir is very important for field development and exploration. Traditional seismic methods for fracture characterization include shear wave birefringence Dok et al., 2001;Angerer et al., 2002;Vetri et al., 2003) and amplitude variations with offset and azimuth (AVOA) (Ruger, 1998;Shen et al., 2002;Hall et al., 2003;Liu et al., 2010;Lynn et al., 2010). These methods are based on the equivalent medium theory with the assumption that fracture dimension and spacing are small relative to the seismic wave length, so a fracture zone behaves like an equivalent anisotropic medium. But fractures on the order of seismic wave length are also very important for enhanced oil recovery, and they are one of the important subsurface scattering sources that generate scattered seismic waves. Willis et al. (2006) developed the Scattering Index method to extract the fracture scattering characteristics by calculating the transfer funtion of a fracture zone. Fang et al. (2011) proposed a modification of the SI method (the Fracture Transfer Function (FTF) method) that leads to a more robust fracture characterization. In this paper, we use both laboratory data and field data to explore the capability of the FTF method. METHODOLOGYThe transfer function of a fractured layer is expressed as where O 1 (ω, θ ) and O 2 (ω, θ ), respectively, are the stacked data from above and below the fracture zone in azimuth θ , O 0 1 (ω) and O 0 2 (ω) are the averages of O 1 (ω, θ ) and O 2 (ω, θ ) over all azimuths, wl is water level.The spatial variation of the strength of fracture scattered waves shows characteristics related to fracture spacing due to interference (Willis et al., 2005;Grandi et al., 2007;Zheng et al., 2011). Fracture scattered waves are observed to be stronger at frequencieswhere FS is fracture spacing and V is velocity.f n is defined as the n-th eigen-frequency of the fracture zone in our study, and f 1 = V 2·FS is the base eigen-frequency. From both laboratory experiments and numerical simulations, we find that, in the direction normal to fracture strike, due to the disruptive nature of fracture scattered waves, notches can be found in FT F at the eigen-frequencies after stacking, in the fracture strike direction, the scattered waves can stack constructively, so peaks appear at the eigen-frequencies after stacking. So the azimuthal variation of FT F(ω, θ ) is larger at the eigen-frequencies given by Equation 2. The eigen-frequencies and the azimuthal variation of FT F after stacking give information about both fracture orientation and spacing.In order to quantify the azimuthal variation of FT F(ω, θ ), which can be used to determine the fracture orientation, we define the fracture orientation function aswhere θ is azimuth, [ω 1 , ω 2 ] is frequency window, the weighting function SDFT F(ω) is the azimuthal standard deviation of FT F, FT F(ω) is the mean of the FT F at frequency ω, N is the number of azimuth...

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“…Stopień rozpoznania intensywności oraz orientacji kierunków spękań (szczelin) jest szczegól-nie ważny w projektowaniu otworów poziomych mających udostępnić złoża o charakterze niekonwencjonalnym (tight, shale), jak również w optymalizacji procesów eksploatacji węglowodorów ze złoża [3,4,5].…”

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Wyznaczanie rozkładu szczelin w formacjach typu shale gas na podstawie azymutalnych pomiarów sejsmicznych

Bartoń

Wilk

2016

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Wyznaczanie rozkładu szczelin w formacjach typu shale gas na podstawie azymutalnych pomiarów sejsmicznych W artykule została zaprezentowana metodyka wyznaczania rozkładu szczelin i ich azymutów dla dwóch horyzontów sejsmicznych odpowiadających stropowi ogniwa Jantaru i formacji z Sasina, tj. poziomów zbiornikowych typu shale gas, na podstawie azymutalnych pomiarów sejsmicznych 3D. Fala sejsmiczna propagująca przez ośrodek geologiczny uzyskuje wyższą prędkość, przechodząc wzdłuż systemu spękań, a niższą prostopadle do nich. Wykorzystanie tego zjawiska umożliwia przeprowadzenie analiz zmian amplitud względem różnych kierunków (azymutów) zapisu sejsmicznego, pozwalając na określenie stopnia zmienności parametrów sprężystych w układzie HTI (horizontal transverse isotropy). Wyznaczony w ten sposób stopień zmienności umożliwia określenie wielkości oraz kierunków rozkładu szczelin rozpatrywanego ośrodka geologicznego. Stopień rozpoznania intensywności oraz orientacji kierunków spękań (szczelin) jest szczególnie ważny w projektowaniu otworów poziomych oraz w optymalizacji procesów eksploatacji węglowodorów ze złoża.Słowa kluczowe: sejsmika azymutalna, aproksymacja, szczelinowatość, shale gas. Determining distribution of fractures in shale gas formations based on azimuthal seismic surveyThis article presents results of a methodology of determining the distribution of fractures and their azimuths for two seismic horizons corresponding to the tops of Jantar member and Sasino formation, i.e. the levels of shale gas type reservoir, based on azimuth 3D seismic data. Seismic wave propagating through the geological medium achieved higher velocity going along the system fracture and a lower perpendicular to them. Use of this phenomenon makes it possible to carry out analyzes of changes in amplitude, with respect to different directions (azimuths) of seismic record, allowing to determine the degree of variability of elastic parameters in a HTI (Horizontal Transverse Isotropy). The specified degree of variation makes it possible, to determine the size and direction of fractures distribution in the geological medium. The degree of the intensity and orientation directions of cracks (fractures), is particularly important in the design of horizontal wells and optimizing the exploitation processes of hydrocarbons from the reservoir.

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PP azimuthal‐amplitudes and ‐acoustic impedance for fractured carbonate reservoir characterization

Cited by 5 publications

References 6 publications

Fracture clustering effect on amplitude variation with offset and azimuth analyses

Fracture clustering effect on amplitude variation with offset and azimuth analyses

Reservoir fracture characterizations from seismic scattered waves

Wyznaczanie rozkładu szczelin w formacjach typu shale gas na podstawie azymutalnych pomiarów sejsmicznych

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