Velocity anisotropy in shales: A petrophysical study

Geophysics ◽  
1997 ◽  
Vol 62 (2) ◽  
pp. 521-532 ◽  
Author(s):  
Lev Vernik ◽  
Xingzhou Liu
Keyword(s):  
Seismic Anisotropy ◽  
Elastic Anisotropy ◽  
Clay Mineralogy ◽  
Fluid Phase ◽  
Black Shales ◽  
P Wave ◽  
Velocity Versus ◽  
Softening Effect ◽  
Porosity Reduction ◽  
Wide Range

Using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content, clay mineralogy, and porosity at a wide range of effective pressure, we find that elastic anisotropy of shales increases substantially with compaction. The effect is attributed to both porosity reduction and smectite‐ to‐illite transformation with diagenesis. A means of kerogen content mapping using velocity versus porosity crossplot for shales is shown. Matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0.4 at total organic carbon (TOC)=15–20%. A strong chemical softening effect was found in shales containing even minor amounts of swelling (smectite) clay when saturated with aqueous solution. This effect results in a significant P‐wave anisotropy reduction as compared to dry and oil‐saturated shales. Since mature black shales are normally oil wet, this effect can only have a local significance restricted to the wellbore wall. Accurate measurements of phase velocities, including velocities at a 45° direction to the bedding plane, allow us to immediately calculate elastic stiffnesses and anisotropic parameters. Intrinsic (high pressure) properties of shales display an ε > δ > 0 relation. Introduction of the bedding‐parallel microcracks in overpressured shales results in a δ decrease when fully fluid saturated and a δ increase when partially gas saturated, with a characteristic effect on the shape of the P‐wave velocity surface at small angles of incidence. Filtering the contribution of the intrinsic anisotropy of shales, it is possible to estimate the pore fluid phase, microcrack density, and aspect ratio parameters using seismic anisotropy measurements.

Seismic anisotropy in exploration and reservoir characterization: An overview

Geophysics ◽  
2010 ◽  
Vol 75 (5) ◽  
pp. 75A15-75A29 ◽  
Author(s):  
Ilya Tsvankin ◽  
James Gaiser ◽  
Vladimir Grechka ◽  
Mirko van der Baan ◽  
Leon Thomsen
Keyword(s):  
Reservoir Characterization ◽  
Seismic Anisotropy ◽  
Body Wave ◽  
Transverse Isotropy ◽  
Time Lapse ◽  
P Wave ◽  
Fracture Detection ◽  
Fracture Characterization ◽  
Anisotropic Models ◽  
Wide Range

Recent advances in parameter estimation and seismic processing have allowed incorporation of anisotropic models into a wide range of seismic methods. In particular, vertical and tilted transverse isotropy are currently treated as an integral part of velocity fields employed in prestack depth migration algorithms, especially those based on the wave equation. We briefly review the state of the art in modeling, processing, and inversion of seismic data for anisotropic media. Topics include optimal parameterization, body-wave modeling methods, P-wave velocity analysis and imaging, processing in the [Formula: see text] domain, anisotropy estimation from vertical-seismic-profiling (VSP) surveys, moveout inversion of wide-azimuth data, amplitude-variation-with-offset (AVO) analysis, processing and applications of shear and mode-converted waves, and fracture characterization. When outlining future trends in anisotropy studies, we emphasize that continued progress in data-acquisition technology is likely to spur transition from transverse isotropy to lower anisotropic symmetries (e.g., orthorhombic). Further development of inversion and processing methods for such realistic anisotropic models should facilitate effective application of anisotropy parameters in lithology discrimination, fracture detection, and time-lapse seismology.

scholarly journals Noncontacting benchtop measurements of the elastic properties of shales

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. C25-C31 ◽  
Author(s):  
Thomas E. Blum ◽  
Ludmila Adam ◽  
Kasper van Wijk
Keyword(s):  
Group Velocity ◽  
Elastic Anisotropy ◽  
P Wave ◽  
Laser Source ◽  
Velocity Versus ◽  
P Wave Velocity ◽  
Least Squares Fit ◽  
In Situ Conditions ◽  
Velocity Information ◽  
Attenuation Anisotropy

We evaluated a laser-based noncontacting method to measure the elastic anisotropy of horizontal shale cores. Whereas conventional transducer data contained an ambiguity between phase and group velocity measurements, small laser source and receiver footprints on typical core samples ensured group velocity information in our laboratory measurements. With a single dense acquisition of group velocity versus group angle on a horizontal core, we estimated the elastic constants [Formula: see text], [Formula: see text], and [Formula: see text] directly from ultrasonic waveforms, and [Formula: see text] from a least-squares fit of modeled to measured group velocities. The observed significant P-wave velocity and attenuation anisotropy in these dry shales were almost surely exaggerated by delamination of clay platelets and microfracturing, but provided an illustration of the new laboratory measurement technique. Although challenges lay ahead to measure preserved shales at in situ conditions in the lab, we evaluated the fundamental advantages of the proposed method over conventional transducer measurements.

New Imaging Approach for Constraining the Azimuth and Dip of Seismic Anisotropy Using Teleseismic P-wave Delays and its Application to the Western United States

2021 ◽  
Author(s):  
Brandon VanderBeek ◽  
Miles Bodmer ◽  
Manuele Faccenda
Keyword(s):  
United States ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Elastic Anisotropy ◽  
P Wave ◽  
Western United States ◽  
Anisotropic Structure ◽  
Low Velocity ◽  
Mantle Mineral ◽  
Juan De Fuca

<p>Despite the well-established anisotropic nature of Earth’s upper mantle, the influence of elastic anisotropy on teleseismic P-wave imaging remains largely ignored. Unmodeled anisotropic heterogeneity can lead to substantial isotropic velocity artefacts that may be misinterpreted as compositional and thermal heterogeneities. Here, we present a new parameterization for imaging arbitrarily oriented hexagonal anisotropy using teleseismic P-wave delays. We evaluate our tomography algorithm by reconstructing geodynamic simulations of subduction that include predictions for mantle mineral fabrics. Our synthetic tests demonstrate that accounting for both the dip and azimuth of anisotropy in the inversion is critical to the accurate recovery of both isotropic and anisotropic structure. We then perform anisotropic inversions using data collected across the western United States and offshore Cascadia. Our preliminary models show a clear circular pattern in the azimuth of anisotropy around the southern edge of the Juan de Fuca slab that is remarkably similar to the toroidal flow pattern inferred from SKS splits. We also image dipping anisotropic domains coincident with the descending Juan de Fuca slab. In contrast to prior isotropic tomographic results, the Juan de Fuca slab in our anisotropic model is characterized by more uniform P-wave speeds and is without an obvious slab hole below ~150 km depth. We also find a general decrease in the magnitude of mantle low-velocity zones throughout the model relative to prior studies. These results highlight the sensitivity of teleseismic P-waves to anisotropic structure and the importance of accounting for anisotropic heterogeneity in the imaging of subduction zones.</p>

scholarly journals Seismic Anisotropy in Subduction Zones: Evaluating the Role of Chloritoid

2021 ◽  
Vol 9 ◽  
Author(s):  
Jungjin Lee ◽  
Mainak Mookherjee ◽  
Taehwan Kim ◽  
Haemyeong Jung ◽  
Reiner Klemd
Keyword(s):  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Elastic Anisotropy ◽  
P Wave ◽  
Stability Field ◽  
S Wave ◽  
Hydrous Minerals ◽  
Rock Samples ◽  
Natural Rock

Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs), are often invoked to explain these observations. However, the elasticity and the LPO of chloritoid, which is one of such hydrous phases relevant in subduction zone settings, are poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples, obtained the LPO-induced seismic anisotropy, and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (VS) and 22% for P-waves (VP), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy with a maximum AVS of 18% and a P-wave anisotropy with an AVP of 10%. The role of chloritoid LPO in seismic anisotropy was evaluated in natural rock samples and a hypothetical blueschist. Our results indicate that the strong LPO of chloritoid along the subduction interface and in subducting slabs can influence the trench-parallel seismic anisotropy in subduction zones with “cold” geotherms.

The elastic properties and anisotropy of artificial compacted clay samples

Geophysics ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. MR1-MR15
Author(s):  
Fei Gong ◽  
Bangrang Di ◽  
Lianbo Zeng ◽  
Jianxin Wei ◽  
Jiwei Cheng ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Elastic Properties ◽  
Transverse Isotropy ◽  
Clay Mineralogy ◽  
Distribution Functions ◽  
P Wave ◽  
Hydrocarbon Reservoir ◽  
Porosity Reduction ◽  
Clay Platelets ◽  
Compaction Stress

Clay minerals are a major component of hydrocarbon reservoir rocks, and they are known to play important roles in the physical and elastic properties of rocks. However, it is difficult to directly measure these properties of single-crystal clays due to their small particle size. Therefore, we have constructed three sets of artificial clay samples with different compaction stresses to investigate the effect of the compaction stress and clay mineralogy on their elastic properties and anisotropy. All of the dry samples are measured by the pulse-transmission method. The results indicate that the compaction stress and clay mineralogy have a significant influence on the physical and elastic properties of the clay samples. The microstructures of clay samples indicate that the clay platelets are aligned almost perpendicularly to the direction of compaction stress, and the ultrasonic velocity analysis validates the assumption of transverse isotropy of our clay samples. The velocities increase with the compaction stress, especially at low stress, which corresponds to the rapid porosity reduction at low stress levels. Velocity anisotropy parameters increase with increasing of compaction stress due to the increase of texture sharpness for clay minerals during the compaction process. The elastic moduli of the clay samples display a significant stress sensitivity and a strong directional dependence, with the Young’s moduli increasing and the Poisson’s ratios decreasing with the compaction stress. A simple theoretical template is used to quantify the orientation distribution functions (ODFs) of clay platelets, and the generalized Legendre coefficients of ODF increase with the increase of compaction stress, especially at low stress. Further, the compressional-wave (P-wave) and shear-wave anisotropy increase with the ODF coefficients [Formula: see text] and [Formula: see text], especially P-wave anisotropy.

Lattice preferred orientation and seismic anisotropy of chloritoid in subduction zone

2021 ◽  
Author(s):  
Jungjin Lee ◽  
Mainak Mookherjee ◽  
Taehwan Kim ◽  
Haemyeong Jung ◽  
Reiner Klemd
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Elastic Anisotropy ◽  
P Wave ◽  
Stability Field ◽  
S Wave ◽  
P Waves ◽  
Hydrous Minerals ◽  
Natural Rock

<p>Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs) are often invoked to explain these observations. However, the elasticity and LPO of chloritoid, which is one such hydrous phases relevant in subduction zone settings, is poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples and obtained the LPO-induced seismic anisotropy and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (V<sub>S</sub>) and 22% for P-waves (V<sub>P</sub>), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy of AV<sub>S</sub> = 18% and a P-wave anisotropy of AV<sub>P</sub> = 10%. Our results indicate that the strong LPO of chloritoid along the hydrated slab-mantle interface and in subducting slabs can influence trench-parallel seismic anisotropy in subduction zones with “cold” geotherms.</p>

scholarly journals Elastic anisotropies of rocks in a subduction and exhumation setting

2021 ◽  
Author(s):  
Michael J. Schmidtke ◽  
Ruth Keppler ◽  
Jacek Kossak-Glowczewski ◽  
Nikolaus Froitzheim ◽  
Michael Stipp
Keyword(s):  
Subduction Zones ◽  
Elastic Anisotropy ◽  
Tectonic Setting ◽  
P Wave ◽  
European Alps ◽  
Data Set ◽  
Wave Velocities ◽  
Wide Range ◽  
P Wave Velocities ◽  
Felsic Rocks

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e. crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian Northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction at the Frank Laboratory of Neutron Physics at the JINR in Dubna, Russia. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation-setting. In subducted lithologies originating from the oceanic crust, the elastic anisotropies range from 1.4 to 5.0 % with average P-wave velocities of 7.01–8.24 km/s and VP / VS-ratios of 1.71–1.76. In the metasediments of the former accretionary prism the elastic anisotropies range from 4.7 to 8.2 %. This tectonic setting displays average P-wave velocities of 6.47–7.23 km/s and VP / VS-ratios of 1.60–1.76. Continental crust which is incorporated in the collisional orogen shows elastic anisotropies ranging from 1.8 to 2.8 % with average P-wave velocities of 6.42–6.51 km/s and VP / VS-ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

scholarly journals Elastic anisotropies of rocks in a subduction and exhumation setting

Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1801-1828
Author(s):  
Michael J. Schmidtke ◽  
Ruth Keppler ◽  
Jacek Kossak-Glowczewski ◽  
Nikolaus Froitzheim ◽  
Michael Stipp
Keyword(s):  
Subduction Zones ◽  
Elastic Anisotropy ◽  
Accretionary Prism ◽  
P Wave ◽  
European Alps ◽  
Data Set ◽  
Wave Velocities ◽  
Wide Range ◽  
P Wave Velocities ◽  
Felsic Rocks

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e., crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation setting. In subducted lithologies originating from the oceanic crust, the P-wave anisotropies (AVPs [%]) range from 1.4 % to 3.7 % with average P-wave velocities of 7.20–8.24 km/s and VP / VS ratios of 1.70–1.75. In the metasediments of the former accretionary prism the AVPs range from 3.7 % to 7.1 %, average P-wave velocities are 6.66–7.23 km/s and VP / VS ratios are 1.61–1.76. Continental crust which is incorporated in the collisional orogen shows AVP ranging from 1.4 % to 2.1 % with average P-wave velocities of 6.52–6.62 km/s and VP / VS ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, and higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

scholarly journals A smart passive MR damper with a hybrid powering system for impact mitigation: An experimental study

2021 ◽  
pp. 1045389X2098808
Author(s):  
S. Jin ◽  
L. Deng ◽  
J. Yang ◽  
S. Sun ◽  
D. Ning ◽  
...  
Keyword(s):  
Impact Velocity ◽  
Mr Damper ◽  
Damping Force ◽  
Softening Effect ◽  
Impact Speed ◽  
Impact Mitigation ◽  
Passive Damper ◽  
Comparison Results ◽  
Wide Range ◽  
The Impact

This paper presents a smart passive MR damper with fast-responsive characteristics for impact mitigation. The hybrid powering system of the MR damper, composed of batteries and self-powering component, enables the damping of the MR damper to be negatively proportional to the impact velocity, which is called rate-dependent softening effect. This effect can keep the damping force as the maximum allowable constant force under different impact speed and thus improve the efficiency of the shock energy mitigation. The structure, prototype and working principle of the new MR damper are presented firstly. Then a vibration platform was used to characterize the dynamic property and the self-powering capability of the new MR damper. The impact mitigation performance of the new MR damper was evaluated using a drop hammer and compared with a passive damper. The comparison results demonstrate that the damping force generated by the new MR damper can be constant over a large range of impact velocity while the passive damper cannot. The special characteristics of the new MR damper can improve its energy dissipation efficiency over a wide range of impact speed and keep occupants and mechanical structures safe.

scholarly journals Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study

2019 ◽  
Vol 24 (1) ◽  
pp. 101-120
Author(s):  
Kajetan Chrapkiewicz ◽  
Monika Wilde-Piórko ◽  
Marcin Polkowski ◽  
Marek Grad
Keyword(s):  
Surface Wave ◽  
Inverse Problems ◽  
Receiver Function ◽  
Joint Inversion ◽  
Wave Dispersion ◽  
Receiver Functions ◽  
P Wave ◽  
Surface Wave Dispersion ◽  
Phase Velocity Dispersion ◽  
Wide Range

AbstractNon-linear inverse problems arising in seismology are usually addressed either by linearization or by Monte Carlo methods. Neither approach is flawless. The former needs an accurate starting model; the latter is computationally intensive. Both require careful tuning of inversion parameters. An additional challenge is posed by joint inversion of data of different sensitivities and noise levels such as receiver functions and surface wave dispersion curves. We propose a generic workflow that combines advantages of both methods by endowing the linearized approach with an ensemble of homogeneous starting models. It successfully addresses several fundamental issues inherent in a wide range of inverse problems, such as trapping by local minima, exploitation of a priori knowledge, choice of a model depth, proper weighting of data sets characterized by different uncertainties, and credibility of final models. Some of them are tackled with the aid of novel 1D checkerboard tests—an intuitive and feasible addition to the resolution matrix. We applied our workflow to study the south-western margin of the East European Craton. Rayleigh wave phase velocity dispersion and P-wave receiver function data were gathered in the passive seismic experiment “13 BB Star” (2013–2016) in the area of the crust recognized by previous borehole and refraction surveys. Final models of S-wave velocity down to 300 km depth beneath the array are characterized by proximity in the parameter space and very good data fit. The maximum value in the mantle is higher by 0.1–0.2 km/s than reported for other cratons.

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