Evaluation of 3D shear-wave anisotropy based on elastic-wave velocity variations around the borehole

Geophysics ◽  
2021 ◽  
pp. 1-47
Author(s):  
Song Xu ◽  
Xiao-Ming Tang ◽  
Carlos Torres-Verdín ◽  
Zhen Li ◽  
Yuanda Su
Keyword(s):  
Shear Wave ◽  
Elastic Anisotropy ◽  
Anisotropy Parameter ◽  
Primary Source ◽  
Shear Velocity ◽  
Fracture Network ◽  
Elastic Wave Velocity ◽  
Azimuthal Anisotropy ◽  
Conventional Procedure ◽  
Radial Anisotropy

Aligned fractures/cracks in rocks are a primary source of elastic anisotropy. In an azimuthally anisotropic formation surrounding a borehole, shear waves split into fast and slow waves that propagate along the borehole and are recorded by a borehole logging tool. However, when the formation has conjugate fractures with orthogonal strike directions, the azimuthal anisotropy vanishes. Hence, azimuthal anisotropy measurements may not be adequate to detect orthogonal fracture sets. We develop a method for obtaining azimuthal and radial shear-wave anisotropy parameters simultaneously from four-component array waveforms. The method utilizes a velocity tomogram around the borehole. Azimuthal and radial anisotropy were determined by integrating shear velocity radiation profile along the radial direction at different azimuthal angles. Results indicate that this approach is reliable for estimating anisotropy properties in aligned crack systems. The advantage of this interpretation method is shown in multiple conjugate crack systems. Field data processing examples are used to verify the application of the proposed technique. Comparison of results against those obtained with a conventional procedure shows that the new method can not only provide estimates of azimuthal anisotropy, but also of the radial anisotropy parameter, which is important in fracture network evaluation.

Direct inversion of 3-D shear wave speed azimuthal and radial anisotropy from surface-wave traveltime data: methodology and applications

2020 ◽  
Author(s):  
Yao Huajian ◽  
Liu Chuanming ◽  
Hu Shaoqian
Keyword(s):  
Surface Wave ◽  
Shear Wave ◽  
Wave Speed ◽  
Joint Inversion ◽  
Azimuthal Anisotropy ◽  
Crust And Upper Mantle ◽  
Shear Wave Speed ◽  
Dispersion Data ◽  
Radial Anisotropy ◽  
Deformation Patterns

<p>Seismic anisotropy plays a key role in understanding deformation patterns of Earth’s material.  Surface wave dispersion data have been widely used to invert for azimuthal and radial anisotropy of shear wave speeds in the crust and upper mantle typically based on a 1-D pointwise inversion scheme. Here we present new methods of inverting for 3-D shear wave speed azimuthal and radial anisotropy directly from surface-wave traveltime data with the consideration of period-dependent surface wave raytracing. For the inversion of 3-D azimuthal anisotropy, our new method includes two steps: (1) inversion for the 3-D isotropic Vsv model directly from Rayleigh wave traveltime data (DSurfTomo; Fang et al., 2015, GJI); (2) joint inversion for both 3-D Vsv azimuthal anisotropy and additional 3-D isotropic Vsv perturbation. The joint inversion can significantly mitigatethe trade-off between the strong heterogeneity and azimuthal anisotropy. We apply the new method (DAzimSurfTomo) (Liu et al., 2019, JGR)to a regional array in Yunnan, southwestern China using the Rayleigh-wave phase velocity dispersion data in the period band of 5-40 s extracted from ambient noise interferometry. The obtained 3-D model of shear wave speed and azimuthal anisotropy indicates differentdeformation styles between the crust and upper mantle insouthern Yunnan. For the inversion of 3-D radial anisotropy, we presented a new inversion matrix that directly inverts Rayleigh and Love wave traveltime data jointly for 3-D Vsv and radial anisotropy parameters (Vsh/Vsv) simultaneously without intermediate steps (Hu et al., submitted to JGR).  The new approach allows for adding the smoothing or model regularization terms directly on the radial anisotropy parameters, which helps to obtain more reliable radial anisotropy structures compared to the previous division approach (Vsh/Vsv) from separate inversion of Vsv and Vsh structures. We apply this new approach (DRadiSurfTomo) to the region around the eastern Himalayan syntaxis using ambient noise dispersion data (5-40s). The obtained 3-D Vs and radial anisotropy models reveals complex distribution of crustal low velocity zones and spatial variation of deformation patterns around the eastern syntaxis region.</p>

Radial anisotropy in Europe from surface waves ambient noise tomography and transdimensional hierarchical inversion

2020 ◽  
Author(s):  
Chloé Alder ◽  
Eric Debayle ◽  
Thomas Bodin ◽  
Anne Paul ◽  
Laurent Stehly ◽  
...  
Keyword(s):  
Group Velocity ◽  
Shear Wave ◽  
Rayleigh Waves ◽  
3D Model ◽  
Joint Inversion ◽  
Shear Velocity ◽  
Dispersion Curves ◽  
Uppermost Mantle ◽  
Radial Anisotropy ◽  
Anisotropy Model

<p>We present a 3D probabilistic model of shear wave velocity and radial anisotropy of the European crust and uppermost mantle mainly focusing on the Alps and the Apennines.</p><p>The model is built using continuous seismic noise recorded between 2010 and 2018 at 1521 broadband stations, including the AlpArray network (Hetényi et al., 2018).</p><p>We use a large dataset of more than 730 000 couples of stations representing as many virtual source-receiver pairs. For each path, we calculate the cross-correlation of continuous vertical- and transverse-components of the noise records in order to get the Green’s function. From the Green’s function, we then obtain the group velocity dispersion curves of Love and Rayleigh waves in the period range 5 to 149 s.</p><p>Our 3D model is built in two steps. First, the dispersion data are used in a linearized least square inversion providing 2D maps of group velocity in Europe at each period. These maps are obtained using the same coverage for Love and Rayleigh waves. Dispersion curves for both Love and Rayleigh waves are then extracted from the maps, at each geographical point. In a second step, these curves are jointly inverted to depth for shear velocity and radial anisotropy. The inversion in done within a Bayesian Monte-Carlo framework integrating some a priori information coming either from PREM (Dziewonski and Anderson 1961) or the recent 3D shear wave model of Lu et al. 2018 performed for the same region.</p><p>Therefore, this joint inversion of Rayleigh and Love data allows us to derive a new 3D model of shear velocity and radial anisotropy of the European crust and uppermost mantle. The isotropic part of our model is consistent with the shear velocity model of Lu et al. 2018. The 3D radial anisotropy model of the region adds new constraints on the deformation of the lithosphere in Europe. Here we present and discuss this new radial anisotropy model, with particular emphasis on the Apennines.</p>

Core-Derived Velocity Systematics, Mississippian Meramec Formation, Oklahoma

SPE Journal ◽  
2021 ◽  
pp. 1-10
Author(s):  
Jing Fu ◽  
Carl Sondergeld ◽  
Chandra Rai
Keyword(s):  
Shear Wave ◽  
Volume Fraction ◽  
Anisotropy Parameter ◽  
Clay Content ◽  
Weight Fraction ◽  
Shear Velocity ◽  
Compressional Wave ◽  
P Wave ◽  
S Wave ◽  
Trend Line

Summary Elastic wave velocities are commonly used to predict porosity, mineralogy, and lithology from formation properties. When only P-wave sonics are available in historical wells, systematics for predicting shear velocities are useful for developing elastic models. Although much research has been done on conventional reservoir velocity systematics, the equivalency for unconventional formations is still a work in progress. There has also been a limited number of research studies with laboratory measures published. Using laboratory pulse transmission ultrasonic data, we created a Vp-Vs systematic for the Meramec Formation in this study. The effects of porosity and mineralogy on velocities are explored, as well as a comparison of Meramec velocity systematics with well-established literature systematics. Vp and Vs measurements were taken on 385 dodecane-saturated core samples from seven Meramec wells (106 vertical and 279 horizontal plugs). S-wave and P-wave anisotropy in Meramec Formation samples used in this study are typically less than 10%. Each sample was also tested for porosity and mineralogy. We find that velocities are more sensitive to porosity than mineralogy by a factor of 10. Below are our equations for predicting Vp and Vs (in km/s), when only clay content and porosity are known. In these equations, φ is the volume fraction pores, and Clays is the weight fraction of clay. These equations are for those samples in which there is low P-wave and S-wave anisotropies:(1)Vp=6.4−1.2*Clays−15.4*φ(R2=0.5),(2)Vs=3.6−0.5*Clays−5.2*φ(R2=0.4). We suggest two methods for calculating Vs from Vp: Ignoring anisotropy, we combined both Vp and Vs measurements from all vertical plugs and low anisotropy horizontal plugs to create a single shear wave predictor; and considering anisotropy, Vp measurements from horizontal plugs were corrected using Thomsen’s compressional wave anisotropy parameter, after which a shear velocity predictor was generated. The shear wave predictors for dodecane-saturated measurements are as follows (all velocities are km/s):(3)Method 1: Vs= 0.90 + 0.42*Vp (R2=0.7),(4)Method 2: Vs= 0.80 + 0.45*Vp (R2=0.6). The residual and estimated error in Eq. 3 is slightly less than in Eq. 4. Even though there is a significant variance in measurement frequency, the Meramec velocity systematic shows good agreement with dipole wireline measurements using the first equation. The Meramec velocity systematics differ significantly from previously published systematics, such as the trend line by Greenberg and Castagna (1992) and the shale trend line by Vernik et al. (2018). Using the correlations by Greenberg and Castagna (1992) for limestone or dolomite, the shear velocities of the samples in this study cannot be predicted. These data have yielded shear wave systematics, which can be used in wireline and seismic investigations. The results suggest that the method of ignoring anisotropy yields a better Vs estimate than the one that takes anisotropy into account. Using well-established shear wave velocity systematics from the published literature can result in an estimated inaccuracy of greater than 16%. It is important to calibrate velocity systematics to the target formation.

scholarly journals Crystallographic texture dependent bulk anisotropic elastic response of additively manufactured Ti6Al4V

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mangesh V. Pantawane ◽  
Teng Yang ◽  
Yuqi Jin ◽  
Sameehan S. Joshi ◽  
Sriswaroop Dasari ◽  
...  
Keyword(s):  
Shear Wave ◽  
Crystallographic Texture ◽  
Elastic Anisotropy ◽  
Shear Velocity ◽  
Elastic Response ◽  
Powder Bed ◽  
Significant Attenuation ◽  
Texture Effect ◽  
Anisotropic Elastic ◽  
Combined Technique

AbstractRapid thermokinetics associated with laser-based additive manufacturing produces strong bulk crystallographic texture in the printed component. The present study identifies such a bulk texture effect on elastic anisotropy in laser powder bed fused Ti6Al4V by employing an effective bulk modulus elastography technique coupled with ultrasound shear wave velocity measurement at a frequency of 20 MHz inside the material. The combined technique identified significant attenuation of shear velocity from 3322 ± 20.12 to 3240 ± 21.01 m/s at 45$$^\circ$$ ∘ and 90$$^\circ$$ ∘ orientations of shear wave plane with respect to the build plane of printed block of Ti6Al4V. Correspondingly, the reduction in shear modulus from 48.46 ± 0.82 to 46.40 ± 0.88 GPa was obtained at these orientations. Such attenuation is rationalized based on the orientations of $$\alpha ^\prime$$ α ′ crystallographic variants within prior columnar $$\beta$$ β grains in additively manufactured Ti6Al4V.

scholarly journals Radial anisotropy and S-wave velocity depict the internal to external zones transition within the Variscan orogen (NW Iberia) 

2021 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Carlos López-Fernández ◽  
Javier Olona ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Ambient Noise ◽  
Variscan Orogeny ◽  
Low Grade ◽  
The West ◽  
Cantabrian Zone ◽  
Variscan Orogen ◽  
Nw Iberia ◽  
Radial Anisotropy

Abstract. The cross-correlation of ambient noise records registered by seismic networks has proven to be a valuable tool to obtain new insights into the crustal structure at different scales. Based on 2- to 14-s-period Rayleigh and Love dispersion data extracted from the seismic ambient noise recorded by 20 three-component broadband stations belonging to two different temporary experiments, we present the first i) upper crustal (1–14 km) high-resolution shear wave velocity and ii) radial anisotropy variation models of the continental crust in NW Iberia. The area of study represents one of the best exposed cross-sections along the Variscan orogen of western Europe, showing the transition between the external eastern zones towards the internal areas in the west. Both the 2-D maps and an E-W transect reveal a close correspondence with the main geological domains of the Variscan orogen. The foreland-fold and thrust-belt of the orogen, the Cantabrian Zone, is revealed by a zone of relatively low shear wave velocities (2.3–3.0 km/s), while the internal zones generally display higher homogeneous velocities (> 3.1 km/s). The boundary between both zones is clearly delineated in the models, depicting the arcuate shape of the orogen grain. The velocity patterns also reveal variations of the bulk properties of the rocks that can be linked to major Variscan structures, such as the basal detachment of the Cantabrian Zone or the stack of nappes involving pre-Variscan basement; or sedimentary features such as the presence of thick syn-orogenic siliciclastic wedges. Overall, the radial anisotropy magnitude varies between −5 and 15 % and increases with depth. The depth pattern suggests that the alignment of cracks is the main source of anisotropy at < 8 km depths, although the intrinsic anisotropy seems to be significant in the West-Asturian Leonese Zone, the low-grade slate belt adjacent to the Cantabrian Zone. At depths > 8 km, widespread high and positive radial anisotropies are observed, caused by the presence of subhorizontal alignments of grains and minerals in relation to the internal deformation of rocks either during the Variscan orogeny or prior to it.

Lithospheric structure of the North American Craton constrained by full waveform inversion

2021 ◽  
Author(s):  
Tong Zhou ◽  
Min Chen ◽  
Ziyi Xi ◽  
Jiaqi Li
Keyword(s):  
Shear Wave ◽  
Wave Speed ◽  
Waveform Inversion ◽  
Continental Lithosphere ◽  
Shear Wave Speed ◽  
The North ◽  
Full Waveform ◽  
Radial Anisotropy ◽  
North American Craton ◽  
Superior Craton

&lt;p&gt;Cratonic lithosphere is believed to be rigid and less deformed during a long period of time. However, the detailed structure of Cratons may bring information of the complex formation and assemblage process of the continental lithosphere. Here, we present the seismic radial anisotropic structure of the North American Craton (NAC) constrained by a regional full-waveform inversion (FWI) with 465,422 high-quality frequency-dependent travel time misfit measurements with the shortest period of 15 s from both the body wave and surface wave recordings of 5,120 stations and 160 earthquakes located in the contiguous U.S and surrounding regions. Started from an initial model constructed by combining US.2016 and Crust1.0 in the crust and S40RTS (isotropic) in the mantle, we are able to have the optimized crustal structure in terms of initial waveform similarity and get rid of existing features from other radially anisotropic mantle models.&lt;/p&gt;&lt;p&gt;Our new model reveals the NAC lithosphere with about +2% voigt shear wave speed anomaly and an average thickness of 200&amp;#8211;250 km beneath the Superior Craton, and becomes thinner towards the eastern, the southern, and the southwestern margins with a thickness decreased to 100&amp;#8211;150 km. The radial anisotropy manifests a layer of higher horizontal shear wave speed V&lt;sub&gt;SH&amp;#160;&lt;/sub&gt;(&amp;#958;=V&lt;sub&gt;SH&lt;/sub&gt;&lt;sup&gt;2&lt;/sup&gt;/V&lt;sub&gt;SV&lt;/sub&gt;&lt;sup&gt;2&lt;/sup&gt;&gt;1) beneath the core of Superior Craton down to around 160 km, where the higher vertical shear wave speed V&lt;sub&gt;SV &lt;/sub&gt;(&amp;#958;&lt;1) is observed beneath 160 km. Such radial anisotropy layering is also observed in the margin of continental lithosphere but with shallower depth. The radial anisotropic layer matches the receiver function results of mid-lithosphere discontinuities of the Craton cores, and the lithosphere conductivity result.&amp;#160;The radial anisotropy layering observation confirms the two-layered lithosphere structure of the NAC, where the upper layer likely represents the original radial anisotropy fabric related to the cooling of the craton core, while the lower layer might be related to the tectonic processes more recently, e.g., accretion .&amp;#160;The lithospheric thinning beneath the NAC margins indicates the deformation of the lithosphere and is likely controlled by the large-scale mantle convection, therefore relates to the further modification process of the NAC.&lt;/p&gt;

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