Acoustic properties of carbonates: Effects of rock texture and implications for fluid substitution

Geophysics ◽  
2008 ◽  
Vol 73 (2) ◽  
pp. B51-B65 ◽  
Author(s):  
Klaas Verwer ◽  
Hendrik Braaksma ◽  
Jeroen A. Kenter
Keyword(s):  
Shear Modulus ◽  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Acoustic Properties ◽  
P Wave ◽  
Poisson's Ratio ◽  
Fluid Substitution ◽  
Data Set ◽  
Rock Types ◽  
Rock Texture

More than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of Miocene (Tortonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. We measured the P- and S-waves of carbonate rocks under dry (humidified) and brine-saturated conditions at [Formula: see text] effective pressure with an ultrasonic pulse transmission technique [Formula: see text]. The data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences. Two major textural groups were distinguished on the basis of trends in plots of compressional-wave velocity versus Poisson’s ratio (a specific ratio of P-wave over S-wave velocity). In granular rocks, the framework of depositional grains is the main medium for acoustic-wave propagation; in crystalline rocks, this medium is provided by a framework of interlocking crystals formed during diagenesis. Rock textures are connected to primary depositionalparameters and a diagenetic overprint through the specific effects on Poisson’s ratio. Calculating acoustic velocities using Gassmann fluid substitution modeling approximates measured saturated velocities for 55% of the samples (3% error tolerance); however, it shows considerable errors because shear modulus changes with saturation. Introducing brine into the pore space may decrease the shear modulus of the rock by approximately [Formula: see text] or, alternatively, increase it by approximately [Formula: see text]. This change in shear modulus is coupled with the texture of the rock. In granular carbonates, the shear modulus decreases; in crystalline and cemented carbonates, it increases with saturation. The results demonstrate the intimate relationship between elastic behavior and the depositional and diagenetic properties of carbonate sedimentary rocks. The results potentially allow the direct extraction of granular and crystalline rock texture from acoustic data alone and may help predict rock types from seismic data and in wells.

P- and S-wave velocity models of shallow dry sand formations from surface wave multimodal inversion

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. R197-R209 ◽  
Author(s):  
Paolo Bergamo ◽  
Laura Valentina Socco
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Power Law ◽  
Poisson’S Ratio ◽  
Real Data ◽  
P Wave ◽  
Poisson's Ratio ◽  
S Wave ◽  
Data Set ◽  
Seismic Characterization

Surficial formations composed of loose, dry granular materials constitute a challenging target for seismic characterization. They exhibit a peculiar seismic behavior, characterized by a nonlinear seismic velocity gradient with depth that follows a power-law relationship, which is a function of the effective stress. The P- and S-wave velocity profiles are then characterized by a power-law trend, and they can be defined by two power-law exponents [Formula: see text] and two power-law coefficients [Formula: see text]. In case of depth-independent Poisson’s ratio, the P-wave velocity profile can be defined using the [Formula: see text] power-law parameters and Poisson’s ratio. Because body wave investigation techniques (e.g., P-wave tomography) may perform ineffectively on such materials because of high attenuation, we addressed the potential of surface-wave method for a reliable seismic characterization of shallow formations of dry, uncompacted granular materials. We took into account the dependence of seismic wave velocity on effective pressure and performed a multimodal inversion of surface-wave data, which allowed the [Formula: see text] and [Formula: see text] profiles to be retrieved. The method requires the selection of multimodal dispersion curve points referring to surface-wave frequency components traveling within the granular media formation and their inversion for the S-wave power-law parameters and Poisson’s ratio. We have tested our method on a synthetic dispersion curve and applied it to a real data set. In both cases, the surficial layer was made of loose dry sand. The test on the synthetic data set confirmed the reliability of the proposed procedure because the thickness and the [Formula: see text], [Formula: see text] profiles of the sand layer were correctly estimated. For the real data, the outcomes were validated by other geophysical measurements conducted at the same site and they were in agreement with similar studies regarding loose sand formations.

Seismic wave velocity investigation at The Geysers‐Clear Lake geothermal field, California

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 819-824 ◽  
Author(s):  
Harsh K. Gupta ◽  
Ronald W. Ward ◽  
Tzeu‐Lie Lin
Keyword(s):  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Poisson Ratio ◽  
Volcanic Field ◽  
P Wave ◽  
Poisson's Ratio ◽  
Clear Lake ◽  
Seismic Wave Velocity ◽  
S Waves ◽  
The Geysers

Analysis of P‐ and S‐waves from shallow microearthquakes in the vicinity of The Geysers geothermal area, California, recorded by a dense, telemetered seismic array operated by the U.S. Geological Survey (USGS) shows that these phases are easily recognized and traced on record sections to distances of 80 km. Regional average velocities for the upper crust are estimated to be [Formula: see text] and [Formula: see text] for P‐ and S‐waves, respectively. Poisson’s ratio is estimated at 23 locations using Wadati diagrams and is found to vary from 0.13 to 0.32. In general, the Poisson’s ratio is found to be lower at the locations close to the steam production zones at The Geysers and Clear Lake volcanic field to the northeast. The low Poisson ratio corresponds to a decrease in P‐wave velocity in areas of high heat flow. The decrease may be caused by fracturing of the rock and saturation with gas or steam.

Elastic impedance parameterization and inversion with Young’s modulus and Poisson’s ratio

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. N35-N42 ◽  
Author(s):  
Zhaoyun Zong ◽  
Xingyao Yin ◽  
Guochen Wu
Keyword(s):  
Parameter Estimation ◽  
Young’S Modulus ◽  
Seismic Data ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Incident Angle ◽  
P Wave ◽  
Poisson's Ratio ◽  
Data Set ◽  
Elastic Impedance

Young’s modulus and Poisson’s ratio are related to quantitative reservoir properties such as porosity, rock strength, mineral and total organic carbon content, and they can be used to infer preferential drilling locations or sweet spots. Conventionally, they are computed and estimated with a rock physics law in terms of P-wave, S-wave impedances/velocities, and density which may be directly inverted with prestack seismic data. However, the density term imbedded in Young’s modulus is difficult to estimate because it is less sensitive to seismic-amplitude variations, and the indirect way can create more uncertainty for the estimation of Young’s modulus and Poisson’s ratio. This study combines the elastic impedance equation in terms of Young’s modulus and Poisson’s ratio and elastic impedance variation with incident angle inversion to produce a stable and direct way to estimate the Young’s modulus and Poisson’s ratio, with no need for density information from prestack seismic data. We initially derive a novel elastic impedance equation in terms of Young’s modulus and Poisson’s ratio. And then, to enhance the estimation stability, we develop the elastic impedance varying with incident angle inversion with damping singular value decomposition (EVA-DSVD) method to estimate the Young’s modulus and Poisson’s ratio. This method is implemented in a two-step inversion: Elastic impedance inversion and parameter estimation. The introduction of a model constraint and DSVD algorithm in parameter estimation renders the EVA-DSVD inversion more stable. Tests on synthetic data show that the Young’s modulus and Poisson’s ratio are still estimated reasonable with moderate noise. A test on a real data set shows that the estimated results are in good agreement with the results of well interpretation.

Changes in dynamic shear moduli of carbonate rocks with fluid substitution

Geophysics ◽  
2009 ◽  
Vol 74 (3) ◽  
pp. E135-E147 ◽  
Author(s):  
Gregor T. Baechle ◽  
Gregor P. Eberli ◽  
Ralf J. Weger ◽  
Jose Luis Massaferro
Keyword(s):  
Shear Modulus ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Water Saturation ◽  
Acoustic Properties ◽  
P Wave ◽  
Shear Moduli ◽  
Water Saturated ◽  
Fluid Interaction

To assess saturation effects on acoustic properties in carbonates, we measure ultrasonic velocity on 38 limestone samples whose porosity ranges from 5% to 30% under dry and water-saturated conditions. Complete saturation of the pore space with water causes an increase and decrease in compressional- and shear-wave velocity as well as significant changes in the shear moduli. Compressional velocities of most water-saturated samples are up to [Formula: see text] higher than the velocities of the dry samples. Some show no change, and a few even show a decrease in velocity. Shear-wave velocity [Formula: see text] generally decreases, but nine samples show an increase of up to [Formula: see text]. Water saturation decreases the shear modulus by up to [Formula: see text] in some samples and increases it by up to [Formula: see text] in others. The average increase in the shear modulus with water saturation is [Formula: see text]; the average decrease is [Formula: see text]. The [Formula: see text] ratio shows an overall increase with water saturation. In particular, rocks displaying shear weakening have distinctly higher [Formula: see text] ratios. Grainstone samples with high amounts of microporosity and interparticle macro-pores preferentially show shear weakening, whereas recrystallized limestones are prone to increase shear strengths with water saturation. The observed shear weakening indicates that a rock-fluid interaction occurs with water saturation, which violates one of the assumptions in Gassmann’s theory. We find a positive correlation between changes in shear modulus and the inability of Gassmann’s theory to predict velocities of water-saturated samples at high frequencies. Velocities of water-saturated samples predicted by Gassmann’s equation often exceed measured values by as much as [Formula: see text] for samples exhibiting shear weakening. In samples showing shear strengthening, Gassmann-predicted velocity values are as much as [Formula: see text] lower than measured values. In 66% of samples, Gassmann-predicted velocities show a misfit to measured water-saturated P-wave velocities. This discrepancy between measured and Gassmann-predicted velocity is not caused solely by velocity dispersion but also by rock-fluid interaction related to the pore structure of carbonates. Thus, a pore analysis should be conducted to assess shear-moduli changes and the resultant uncertainty for amplitude variation with offset analyses and velocity prediction using Gassmann’s theory.

scholarly journals Experimental Investigation on the Correlation between Dynamic Ultrasonic and Mechanical Properties of Sandstone Subjected to Uniaxial Compression

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Yunjiang Sun ◽  
Jianping Zuo ◽  
Yue Shi ◽  
Zhengdai Li ◽  
Changning Mi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Ultrasonic Wave ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Poisson’S Ratio ◽  
P Wave ◽  
Poisson's Ratio ◽  
Ultrasonic Wave Velocity ◽  
P Wave Velocity

Ultrasonic wave velocity is effective to evaluate anisotropy property and predict rock failure. This paper investigates the correlation between dynamic ultrasonic and mechanical properties of sandstones with different buried depths subjected to uniaxial compression tests. The circumferential anisotropy and axial wave velocity of sandstone are obtained by means of ultrasonic wave velocity measurements. The mechanical properties, including Young’s modulus and uniaxial compressive strength, are positively correlated with the axial P wave velocity. The average angles between the sandstone failure plane and the minimum and maximum wave directions are 35.8° and 63.3°, respectively. The axial P wave velocity almost keeps constant, and the axial S wave velocity has a decreasing trend before the failure of rock specimen. In most rock samples under uniaxial compression, shear failure occurs in the middle and splitting appears near both sides. Additionally, the dynamic Young’s modulus and dynamic Poisson’s ratio during loading are obtained, and the negative values of the Poisson’s ratio occur at the initial compression stage. Distortion and rotation of micro/mesorock structures may be responsible for the negative Poisson’s ratio.

Predicting Vp and constrained modulus reduction curve based on Vs and shear modulus reduction curve in accordance with poroelastic theory

Géotechnique ◽  
2021 ◽  
pp. 1-39
Author(s):  
Chi-Chin Tsai ◽  
Hsing-Wen Liu ◽  
Domniki Asimaki
Keyword(s):  
Shear Modulus ◽  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Site Response ◽  
Vertical Motion ◽  
Poisson's Ratio ◽  
Reduction Curve ◽  
Constrained Modulus ◽  
Poroelastic Theory ◽  
Modulus Reduction

The compression wave velocity (Vp) of sediments plays a key role in seismic wave amplification of vertical motion and is required in site response analysis. However, such information is usually lacking during field exploration (e.g., surface wave method) because only shear wave velocity (Vs) is obtained. This study aims to predict Vp based on Vs empirically and theoretically, especially focusing on saturated conditions. The empirical approach is to establish the Vp correlation dependency on Poisson's ratio and Vs, and the theoretical approach is based on poroelastic theory that accounts for the interaction between fluid and soil skeleton. The Engineering Geological Database for the Taiwan Strong Motion Instrumentation Program and the Kiban Kyoshin Network database in Japan are adopted to establish an empirical model and validate poroelastic theory. The validated poroelastic approach is used to develop a constrained modulus reduction curve dependency on the porosity, Vs, Poisson's ratio, and degree of saturation with a shear modulus reduction curve. The proposed approach can be used to develop generic Vp profiles and constrained modulus reduction curves for the site response to vertical motion given a site specific Vs profile.

scholarly journals A single Rayleigh mode may exist with multiple values of phase-velocity at one frequency

2020 ◽  
Vol 222 (1) ◽  
pp. 582-594
Author(s):  
Thomas Forbriger ◽  
Lingli Gao ◽  
Peter Malischewsky ◽  
Matthias Ohrnberger ◽  
Yudi Pan
Keyword(s):  
Phase Velocity ◽  
Rayleigh Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Poisson’S Ratio ◽  
P Wave ◽  
Poisson's Ratio ◽  
Wave Number ◽  
Homogeneous Layer ◽  
Rayleigh Mode

SUMMARY Other than commonly assumed in seismology, the phase velocity of Rayleigh waves is not necessarily a single-valued function of frequency. In fact, a single Rayleigh mode can exist with three different values of phase velocity at one frequency. We demonstrate this for the first higher mode on a realistic shallow seismic structure of a homogeneous layer of unconsolidated sediments on top of a half-space of solid rock (LOH). In the case of LOH a significant contrast to the half-space is required to produce the phenomenon. In a simpler structure of a homogeneous layer with fixed (rigid) bottom (LFB) the phenomenon exists for values of Poisson’s ratio between 0.19 and 0.5 and is most pronounced for P-wave velocity being three times S-wave velocity (Poisson’s ratio of 0.4375). A pavement-like structure (PAV) of two layers on top of a half-space produces the multivaluedness for the fundamental mode. Programs for the computation of synthetic dispersion curves are prone to trouble in such cases. Many of them use mode-follower algorithms which loose track of the dispersion curve and miss the multivalued section. We show results for well established programs. Their inability to properly handle these cases might be one reason why the phenomenon of multivaluedness went unnoticed in seismological Rayleigh wave research for so long. For the very same reason methods of dispersion analysis must fail if they imply wave number kl(ω) for the lth Rayleigh mode to be a single-valued function of frequency ω. This applies in particular to deconvolution methods like phase-matched filters. We demonstrate that a slant-stack analysis fails in the multivalued section, while a Fourier–Bessel transformation captures the complete Rayleigh-wave signal. Waves of finite bandwidth in the multivalued section propagate with positive group-velocity and negative phase-velocity. Their eigenfunctions appear conventional and contain no conspicuous feature.

scholarly journals Ground instability of sinkhole areas indicated by elastic moduli and seismic attributes

2020 ◽  
Vol 222 (1) ◽  
pp. 289-304
Author(s):  
S H Wadas ◽  
S Tschache ◽  
U Polom ◽  
C M Krawczyk
Keyword(s):  
Shear Modulus ◽  
Shear Wave ◽  
Poisson’S Ratio ◽  
Elastic Moduli ◽  
Wave Reflection ◽  
P Wave ◽  
Poisson's Ratio ◽  
Dynamic Shear Modulus ◽  
Seismic Profiles ◽  
Low Shear

SUMMARY Elastic moduli derived from vertical seismic profiles (VSPs) and 2-D SH-wave reflection seismic profiles are used to characterize mechanical properties of rocks in sinkhole areas. VP and VS were used to calculate the Poisson’s ratio and the dynamic shear modulus. The study shows that 2-D shear wave reflection seismics is suited to depict the heterogeneities of the subsurface induced by subsurface erosion. Low shear wave velocities of ca. 120–350 m s–1 and low shear strength values between 25 and 250 MPa are identified for the subsurface erosion horizon that consists of soluble Permian evapourites and the disturbed overlying deposits. These low values are a result of cavities and fractures induced by dissolution, creating unstable zones. In compliance with the shear modulus the Poisson’s ratio derived from the VSPs shows values of 0.38–0.48 for both the presumed subsurface erosion horizon, and the deposits above. This is a further indicator of reduced underground stability. In the VSPs, anomalies of the shear modulus and the Poisson’s ratio correlate with low electrical resistivities of less than 10 Ωm from borehole logs, indicating high conductivity due to fluid content. Further investigation reveals a conversion of S-to-P wave for the subsurface erosion horizon, which is probably the result of dipping layers and an oriented fracture network. Seismic attribute analysis of the 2-D sections shows strong attenuation of high frequencies and low similarity of adjacent traces, which correlate with the degree of subsurface erosion induced wave disturbance of the underground.

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