scholarly journals STUDY OF ELASTIC PROPERTIES AS FUNCTION OF TEMPERATURE IN ANISOTROPIC CRACKED MEDIA: AN ULTRASONIC APPROACH

2018 ◽  
Vol 36 (3) ◽  
pp. 1
Author(s):  
José Jésus Silva Sobrinho ◽  
José J. S. de Figueiredo ◽  
Rafael L. Lima ◽  
Léo Kirchhof Santos ◽  
Murillo J. Nascimento
Keyword(s):  
Elastic Properties ◽  
Steam Injection ◽  
Good Alternative ◽  
Seismic Velocities ◽  
S Wave ◽  
Wave Velocities ◽  
Heating And Cooling ◽  
Secondary Cracks ◽  
Anisotropy Parameters ◽  
The Difference

ABSTRACT. The study of seismic wave velocities and their related anisotropy parameters provides important tools to the study of Earth’s subsurface. The analysis of temperature’s influence in the elastic properties of synthetic rocks, e.g., may be a good alternative for modelling the response of elastic properties of rocks surrounding deep wells and/or that are submitted to the process of steam injection. In order to understand the effects of temperature on the elastic parameters, in this work we constructed four porous synthetic sandstones, one representing an uncracked medium and three cracked samples. They were submitted to variable temperatures, while their elastic properties were calculated during heating and cooling processes. It was noted that P- and S-wave velocities decreased with increasing temperature. This behavior may be caused by changes in the background stiffness and by the generation of secondary cracks inside the samples. However, P- and S- anisotropy parameters were not affected by the changes in temperature. This can be an indicative that randomly distributed secondary cracks were created. Other indicative of secondary cracking formation can be associated to the difference between seismic velocities during the heating and cooling processes.Keywords: Cracked media, Anisotropy, Temperature dependence, Elastic parameters.RESUMO. O estudo das ondas sísmicas e de seus parâmetros anisotrópicos associados fornece ferramentas importantes para o estudo da subsuperfície da Terra. A análise da influência da temperatura nos parâmetros elásticos de rochas sintéticas, por exemplo, pode ser uma boa alternativa para modelar a resposta das propriedades elásticas de rochas circundando poços profundos e/ou que são submetidas a processos de injeção de vapor. Para entender os efeitos da temperatura nos parâmetros elásticos, neste trabalho construímos quatro arenitos sintéticos porosos, um representando um meio não-fissurado e três amostras fissuradas. As amostras foram submetidas a temperaturas variadas, enquanto suas propriedades elásticas foram calculadas ao longo dos processos de aquecimento e resfriamento. Notou-se que as velocidades das ondas P e S diminuíram com o aumento da temperatura. Esse comportamento talvez seja causado por variações na rigidez do background e pela formação de fissuras secundárias nas amostras. Entretanto, os parâmetros anisotrópicos P e S não foram afetados pelas mudanças de temperatura. Isso pode ser considerado um indicativo de que fissuras secundárias distribuídas aleatoriamente foram formadas. Outro indicador da formação de fissuras secundárias pode ser associado à diferença entre as velocidades sísmicas durante os processos de aquecimento e resfriamento.Palavras-chave: Meios fissurados, aniostropia, dependência de temperatura, parâmetros elásticos.

Predicting acoustic-wave velocities and fluid sensitivity to elastic properties in fractured carbonate formation

2017 ◽  
Vol 5 (1) ◽  
pp. SB69-SB80 ◽  
Author(s):  
Jingjing Xu ◽  
Maojin Tan ◽  
Xiaochang Wang ◽  
Chunping Wu
Keyword(s):  
Elastic Properties ◽  
Carbonate Rocks ◽  
Seismic Inversion ◽  
Carbonate Reservoir ◽  
S Wave ◽  
Mineral Concentration ◽  
Fracture Porosity ◽  
Wave Velocities ◽  
Carbonate Formation ◽  
Fractured Carbonate

Estimation of S-wave velocity is one of the most critical steps for prestack seismic inversion. Based on the petrophysical model of fractured carbonate rocks, theoretical methods are firstly investigated for estimating P- and S-wave velocities in the presence of fractures. Then, the methods of calculating elastic properties in fractured carbonate rocks are discussed. The mineral concentration, total porosity, and fracture porosity from core X-ray diffraction and routine core measurements or log interpretation results are used to estimate the P- and S-wave velocities. In the given carbonate rock model, the elastic properties of carbonate rocks with different porosity and fractures are calculated. Two field tests prove that the proposed new method is effective and accurate. Furthermore, the model is useful for fluid identification, which is one of the most outstanding problems for carbonate reservoir description. The simulation results suggest that the larger the fracture porosity is, the easier fluid typing. In Tahe Oilfield, the elastic properties of different fluid zones indicate that bulk modulus and Young’s modulus are more sensitive to fluid than shear modulus, the Lamé constant, and Poisson’s ratio.

Seismic Velocities and Attenuation from Borehole Measurements near the Parkfield Prediction Zone, Central California

1989 ◽  
Vol 5 (3) ◽  
pp. 513-537 ◽  
Author(s):  
James F. Gibbs ◽  
Edward F. Roth
Keyword(s):  
P Wave ◽  
Depth Interval ◽  
Seismic Velocities ◽  
S Wave ◽  
Wave Source ◽  
Central California ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Average Shear ◽  
Parkfield Earthquake

Shear (S)- and compressional (P)- wave velocities were measured to a depth of 195 m in a borehole near the San Andreas fault where a recurrence of a moderate Parkfield earthquake is predicted. S-wave velocities determined from orthogonal directions of the S-wave source show velocity differences of approximately 20 percent. An average shear-wave Q of 4 was determined in relatively unconsolidated sands and gravels of the Paso Robles Formation in the depth interval 57.5-102.5 m.

Comparison of seismic upscaling methods: From sonic to seismic

Geophysics ◽  
2009 ◽  
Vol 74 (2) ◽  
pp. WA3-WA14 ◽  
Author(s):  
Dileep K. Tiwary ◽  
Irina O. Bayuk ◽  
Alexander A. Vikhorev ◽  
Evgeni M. Chesnokov
Keyword(s):  
Elastic Wave ◽  
Pair Correlation ◽  
P Wave ◽  
Frequency Bandwidth ◽  
Frequency Range ◽  
S Wave ◽  
Wave Velocities ◽  
Backus Averaging ◽  
The Difference ◽  
Gas Bearing

The term “upscaling” used here means a prediction of elastic-wave velocities at lower frequencies from the velocities at higher frequencies. Three different methods of upscaling are considered, including the simple averaging, Backus averaging, and pair correlation function methods. These methods are applied to upscale the elastic-wave velocities measured at sonic frequencies ([Formula: see text], logging data) available for a well penetrating layers of gas-bearing shales and carbonates. As a result, a velocity distribution over depth for [Formula: see text] and [Formula: see text] is found in the frequency range of [Formula: see text]. The difference in the results obtained for a particular depth by the three theoretical methods in the surface seismic frequency bandwidth [Formula: see text] is [Formula: see text] for P-wave and [Formula: see text] for S-wave velocity. This difference is attributed to different theoretical backgrounds underlying these methods.

scholarly journals A method for determining gas-hydrate or free-gas saturation of porous media from seismic measurements

Geophysics ◽  
2006 ◽  
Vol 71 (3) ◽  
pp. N21-N32 ◽  
Author(s):  
Matthias Zillmer
Keyword(s):  
Porous Medium ◽  
Bulk Density ◽  
Gas Hydrate ◽  
Pore Space ◽  
Seismic Velocities ◽  
S Wave ◽  
Free Gas ◽  
Gas Saturation ◽  
Wave Velocities ◽  
Standard Deviations

The occurrence of gas hydrate or free gas in a porous medium changes the medium’s elastic properties. Explicit formulas for gas-hydrate or free-gas saturation of pore space on the basis of the Frenkel-Gassmann equations describe the elastic moduli and seismic velocities of a porous medium for low frequencies. A key assumption of the model is that either gas hydrate or free gas is present in the pore space in addition to water. Under this assumption, the method uses measured P- and S-wave velocities and bulk density along with estimates of the moduli and densities of the solid and fluid phases present to determine whether gas or hydrate is present. The method then determines the saturation level of either the gas or the hydrate. I apply the method to published velocity and density data from seismic studies at the antarctic Shetland margin and at the Storegga slide, offshore Norway, and to borehole log and core data from Ocean Drilling Program (ODP) Leg 164 at Blake Ridge, offshore South Carolina. A sensitivity analysis reveals that the standard deviations of the gas-hydrate and free-gas saturations reach 30%–70% of the saturations if the standard deviations of the P- and S-wave velocities and of the bulk density are [Formula: see text] and [Formula: see text], respectively. I conclude that a reliable quantification of gas hydrate and free gas can be achieved by seismic methods only if the seismic velocities and bulk density of the medium are determined with high accuracy from the measured data.

scholarly journals Measuring ultrasonic characterisation to determine the impact of TOC and the stress field on shale gas anisotropy

2013 ◽  
Vol 53 (1) ◽  
pp. 245 ◽  
Author(s):  
Yazeed Altowairqi ◽  
Reza Rezaee ◽  
Milovan Urosevic ◽  
Claudio Delle Piane
Keyword(s):  
Elastic Properties ◽  
Shale Gas ◽  
Ultrasonic Transducers ◽  
S Wave ◽  
Gas Reservoirs ◽  
Wave Velocities ◽  
Degree Of Anisotropy ◽  
The Impact ◽  
The Relationship ◽  
Dynamic Elastic Properties

While the majority of natural gas is produced from conventional sources, there is significant growth from unconventional sources, including shale-gas reservoirs. To produce gas economically, candidate shale typically requires a range of characteristics, including a relatively high total organic carbon (TOC) content, and it must be gas mature. Mechanical and dynamic elastic properties are also important shale characteristics that are not well understood as there have been a limited number of investigations of well-preserved samples. In this study, the elastic properties of shale samples are determined by measuring wave velocities. An array of ultrasonic transducers are used to measure five independent wave velocities, which are used to calculate the elastic properties of the shale. The results indicated that for the shale examined in this research, P- and S-wave velocities vary depending on the isotropic stress conditions with respect to the fabric and TOC content. It was shown that the isotropic stress significantly impacts velocity. In addition, S-wave anisotropy was significantly affected by increasing stress anisotropy. Stress orientation, with respect to fabric orientation, was found to be an important influence on the degree of anisotropy of the dynamic elastic properties in the shale. Furthermore, the relationship between acoustic impedance (AI) and TOC was established for all the samples.

Estimation of Velocity Structures in the Grenoble Basin, France, Using Pseudo Earthquake Horizontal-to-Vertical Spectral Ratio from Microtremors

2021 ◽  
Vol 111 (2) ◽  
pp. 627-653
Author(s):  
Eri Ito ◽  
Cécile Cornou ◽  
Fumiaki Nagashima ◽  
Hiroshi Kawase
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Empirical Method ◽  
S Wave ◽  
Wave Velocities ◽  
Strong Linear Correlation ◽  
Large Velocity ◽  
The Difference

ABSTRACT Based on the diffuse field concept for a horizontal-to-vertical spectral ratio of earthquakes (eHVSR), the effectiveness of eHVSRs to invert P- and S-wave velocity structures down to the seismological bedrock (with the S-wave velocity of 3  km/s or higher) has been shown in several published works. An empirical method to correct the difference between eHVSR and a horizontal-to-vertical ratio of microtremors (mHVSR), which is called earthquake-to-microtremor ratio (EMR), has also been proposed for strong-motion sites in Japan. However, the applicability of EMR outside of Japan may not be warranted. We test EMR applicability for the Grenoble basin in France with plentiful microtremor data together with observed weak-motion recordings at five sites. We thereby establish a systematic procedure to estimate the velocity structure from microtremors and delineate the fundamental characteristics of the velocity structures. We first calculate the EMR specific for the Grenoble basin (EMRG) and calculate pseudo eHVSR (pHVSR) from EMRG and mHVSR. We compare the pHVSRs with the eHVSRs at five sites and find sufficient similarity to each other. Then, we invert velocity structures from eHVSRs, pHVSRs, and mHVSRs. The velocity structures from eHVSRs are much closer to those from pHVSRs than those from mHVSRs. We need to introduce a number of layers with gradually increasing S-wave velocities below the geological basin boundary from a previous gravity study because the theoretical eHVSR of the model with a large velocity contrast has larger peak amplitudes than the observed. The depth of the S-wave velocity of 1.3  km/s (Z1.3) shows a strong, linear correlation with the geological boundary depth. Finally, we apply our validated methodology and invert velocity structures using pHVSRs at 14 sites where there are no observed earthquakes. The overall picture of Z1.3 at a cross section in the northeastern part of the basin corresponds to the geological boundary.

Viscoelasticity of precompacted unconsolidated sand with viscous cement

Geophysics ◽  
2006 ◽  
Vol 71 (2) ◽  
pp. T31-T40 ◽  
Author(s):  
Klaus C. Leurer ◽  
Jack Dvorkin
Keyword(s):  
Viscous Fluid ◽  
Contact Stiffness ◽  
Frequency Dispersion ◽  
P Wave ◽  
Seismic Velocities ◽  
Effective Pressure ◽  
S Wave ◽  
Normal Stiffness ◽  
Cemented Sand ◽  
Wave Velocities

The elastic properties of sand strongly depend on the grains’ contact stiffness, which can be increased significantly by solid matter and, depending on frequency, viscous fluid acting as contact cement. To calculate seismic velocities in precompacted fluid-cemented sand, we examine how a small amount of viscous fluid at the grain contacts influences their normal and tangential stiffnesses as a function of effective pressure. Using the Hertz-Mindlin approach and considering oscillatory loading in addition to precompaction of a combination of two elastic spheres, we extend the dry-contact elastic theory by a viscoelastic formulation. Here, we describe the radial flow of the fluid cement induced by the oscillations of the grains’ surfaces around the direct contact, a process that leads to a complex normal stiffness and stiffness/frequency dispersion. In the resulting combined model, the low-frequency real part of the complex normal stiffness identical is to the original Hertz-Mindlin expression. The magnitude of the dispersion is governed by the amount of viscous cement; magnitude decreases as effective pressure increases. The frequency of the maximum imaginary part of the normal stiffness is determined mainly by cement viscosity and contact geometry. The tangential contact stiffness virtually is not influenced by the viscous fluid. Comparison of predicted results with data from pulse transmission experiments (500 kHz) on glass beads with two different fluids shows an excellent fit in P-wave velocities [Formula: see text], whereas S-wave velocities [Formula: see text] are systematically overestimated by the model. The experimental results confirm, however, the predicted change with effective pressure in the [Formula: see text] ratio for both examined cases as well as reflect the predicted increase in [Formula: see text] and [Formula: see text], respectively, between the two cases. This implies that our viscoelastic formulation represents a reasonable way to describe the role of viscous cement in sand.

Seismic Microzonation for Denizli Metropolitan Area, Turkey

2015 ◽  
Vol 802 ◽  
pp. 40-44
Author(s):  
Ali Aydin ◽  
Erdal Akyol ◽  
Mahmud Gungor ◽  
Nuray Soyatik ◽  
Suat Tasdelen
Keyword(s):  
Urban Areas ◽  
Seismic Refraction ◽  
Seismic Microzonation ◽  
Seismic Velocities ◽  
Two Dimensional ◽  
S Wave ◽  
City Center ◽  
Wave Velocities ◽  
Municipal Authority ◽  
Use Studies

This study presents microzonation of the Denizli city center, is about 225 km2. It is mainly rely on t seismic velocities of the tested soil. For seismic microzonation area of has been selected as the study area. Seismic refraction methods have been used to generate two-dimensional profiles at 310 locations. These p and s wave velocities are used to estimate boundaries of the velocities at every 2 and 5 m intervals up to a depth of 60 m. The results are satisfactory for urban planning and it can successfully be used in urban areas. The municipal authority may be considered to use the results for land use studies.

scholarly journals Elastic properties of continental carbonates: From controlling factors to an applicable model for acoustic-velocity predictions

Geophysics ◽  
2019 ◽  
Vol 84 (1) ◽  
pp. MR45-MR59 ◽  
Author(s):  
Jean-Baptiste Regnet ◽  
Jérôme Fortin ◽  
Aurélien Nicolas ◽  
Matthieu Pellerin ◽  
Yves Guéguen
Keyword(s):  
Aspect Ratio ◽  
Elastic Properties ◽  
Carbonate Rocks ◽  
Effective Medium ◽  
Acoustic Velocity ◽  
Controlling Factors ◽  
S Wave ◽  
Wave Velocities ◽  
Diagenetic Alteration ◽  
Continental Carbonates

We have provided new insights into the controlling factors of elastic properties in continental carbonate rocks and introduced an applicable model for acoustic-velocity predictions in such a medium. Petrophysical properties (porosity, permeability, P- and S-wave velocities) from laboratory measurements have been coupled with thin-section observations and characterizations, and X-ray diffraction (XRD) analyses. A major achievement is the establishment of the link between the mineralogical composition and the P- and S-wave velocity dispersion at a given porosity. This reflects the subtle interplay between physicochemical and biological precipitation of continental carbonates, which can also be associated with a strong influence of detrital mineralogical inputs. The result is a mineralogical commixture, coupled to a wide array of pore types inherited from the strong ability of carbonate rocks to undergo diagenetic alteration. The proposed model takes into account the elastic moduli of the minerals, porosity, and pore shape, and it is based on the effective medium theory. We have considered the case in which the medium contained randomly oriented pores with different aspect ratios. Overall, the fit between the predicted trends and the experimental data is fairly good, especially for calcite and quartz matrix mineralogy. The results are even better when considering mineralogy inferred from XRD data, although in some case, and despite the aspect ratio variation in both simulations, the model fails to accurately predict the P-wave velocities. This probably means that another factor is at stake beside mineralogy. This can be explained by the limitation of the effective medium approach, which oversimplifies the reality and fails to account for the variability of some aspect ratio from one inclusion to another.

Seismological studies in a rock body at Chalk River, Ontario and their relation to fractures

1982 ◽  
Vol 19 (8) ◽  
pp. 1535-1547 ◽  
Author(s):  
C. Wright
Keyword(s):  
Wave Velocity ◽  
Test Site ◽  
P Wave ◽  
Seismic Velocities ◽  
S Wave ◽  
P Waves ◽  
Rock Body ◽  
Near Surface ◽  
Wave Velocities ◽  
P Wave Velocity

Seismological experiments have been undertaken at a test site near Chalk River, Ontario that consists of crystalline rocks covered by glacial sediments. Near-surface P and S wave velocity and amplitude variations have been measured along profiles less than 2 km in length. The P and S wave velocities were generally in the range 4.5–5.6 and 2.9–3.2 km/s, respectively. These results are consistent with propagation through fractured gneiss and monzonite, which form the bulk of the rock body. The P wave velocity falls below 5.0 km/s in a region where there is a major fault and in an area of high electrical conductivity; such velocity minima are therefore associated with fracture systems. For some paths, the P and 5 wave velocities were in the ranges 6.2–6.6 and 3.7–4.1 km/s, respectively, showing the presence of thin sheets of gabbro. Temporal changes in P travel times of up to 1.4% over a 12 h period were observed where the sediment cover was thickest. The cause may be changes in the water table. The absence of polarized SH arrivals from specially designed shear wave sources indicates the inhomogeneity of the test site. A Q value of 243 ± 53 for P waves was derived over one relatively homogeneous profile of about 600 m length. P wave velocity minima measured between depths of 25 and 250 m in a borehole correlate well with the distribution of fractures inferred from optical examination of borehole cores, laboratory measurements of seismic velocities, and tube wave studies.

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