Sonic Frequency Range Research Articles

Laboratory measurements of water saturation effects on the acoustic velocity and attenuation of sand packs in the 1–20 kHz frequency range

AbstractWe present novel experimental measurements of acoustic velocity and attenuation in unconsolidated sand with water saturation within the sonic (well‐log analogue) frequency range of 1–20 kHz. The measurements were conducted on jacketed sand packs with 0.5‐m length and 0.069‐m diameter using a bespoke acoustic pulse tube (a water‐filled, stainless steel, thick‐walled tube) under 10 MPa of hydrostatic confining pressure and 0.1 MPa of atmospheric pore pressure. We assess the fluid distribution effect on our measurements through an effective medium rock physics model, using uniform and patchy saturation approaches. Our velocity and attenuation (Q−1) are accurate to ±2.4% and ±5.8%, respectively, based on comparisons with a theoretical transmission coefficient model. Velocity decreases with increasing water saturation up to ∼75% and then increases up to the maximum saturation. The velocity profiles across all four samples show similar values with small differences observed around 70%–90% water saturation, then converging again at maximum saturation. In contrast, the attenuation increases at low saturation, followed by a slight decrease towards maximum saturation. Velocity increases with frequency across all samples, which contrasts with the complex frequency‐dependent pattern of attenuation. These results provide valuable insights into understanding elastic wave measurements over a broad frequency spectrum, particularly in the sonic range.

Well integrity evaluation using acoustic and electromagnetic measurements

The evaluation of downhole well integrity is an important business for the oil and gas industry. It is driven primarily by the need to optimize production while maintaining a safe environment despite the inexorable corrosion of casing strings and other harsh downhole conditions. Furthermore, with aging infrastructure, evaluating well integrity to plan plug and abandonment or slot recovery projects is critically important. Many technologies have been developed to address the challenges of evaluating casing and cement integrity under varied downhole conditions. These technologies are necessarily growing increasingly more sophisticated to meet the requirements of evaluating multiple cemented casing strings. In particular, wireline cased-hole logging techniques based on electromagnetic (EM) and acoustic techniques have been applied to casing corrosion and cement integrity evaluation. The acoustic measurement techniques deployed for well integrity evaluation typically include the sonic frequency range of tens of kilohertz up to the ultrasonic frequency range of megahertz. The frequency ranges are appropriate for characteristic resolutions of decimeters down to millimeters for sonic and ultrasonic measurements, respectively. These techniques are sensitive to the elastic properties of materials in the well completion and crucial for assessing zonal isolation. In the domain of evaluating corrosion in one or multiple casing strings, the traditional measurement approach uses EM techniques, which are sensitive to the metal thickness, the electrical conductivity (the inverse of electrical resistivity), and the magnetic permeability of ferromagnetic pipes. The spectrum of common EM casing inspection techniques encompasses a frequency range between quasi-static (direct current) up to about 100 kHz. More recently, transient EM or pulsed-field eddy current tools have been introduced. Specific physics and challenges associated with well integrity measurements must be understood and considered in existing and emerging technology solutions.

Effective elastic properties of porous rocks with fluid-filled vugs

The problem of determination of the effective elastic properties, particularly, the velocity and attenuation of the compressional wave propagating in porous rocks containing fluid-filled vugs is considered. Usually the correct interpretation of double- or triple-porosity formations using sonic logs is a complex problem, even nowadays with the use of the most advanced inversion algorithms and the contribution of other petrophysical tools. In this work, the proposed model considers spherical inclusions filled with viscous or ideal fluids aimed to represent geological vugs. This approach also considers the cases of “open” and “closed” interfaces at the boundary between the porous rock and the vug. To describe the propagation of elastic waves in porous rocks, the well-known Biot's theory is implemented. The calculations were fulfilled for the incidence of plane compressional harmonic waves. As the first step of performed calculations the so-called one-particle problem is solved. Then, the first order (single-scattering) approximation is applied to calculate the effective wave number of elastic waves propagating in a poroelastic rock containing sets of randomly distributed vugs. The results reported here show that the hydrodynamic effects associated with the fluid filtration at the boundaries between the vugs and the porous rock at the scale of the incident compressional wave, lead to significant frequency dispersion of the effective elastic wave velocity and its correspondent Q-factor. These hydrodynamic effects on the elastic properties are clearly appreciated at the sonic log frequency range. From the findings of this paper, it can be sustained that the elastic response of the fluid viscosity in the vugs is not so significant. This implies that it is possible to use the simple model of an ideal fluid in the vugs.

Seismic vis-a-vis sonic attenuation in gas hydrate bearing sediments of Krishna-Godavari basin, Eastern Margin of India

Seismic velocities in the sediments containing gas hydrates show a marked increase compared to the background, intuitively implying that there would be a reduction in the seismic attenuation (Q−1) of such sediments. However, the attenuation measurements carried out in the sonic frequency range from various gas hydrate provinces show that there is a notable increase in seismic attenuation within the gas hydrate layers and the results obtained are counter-intuitive. In this work we try to compare the attenuation derived by applying frequency shift method to the multichannel seismic (MCS) and sonic data sets at the same location in the Krishna-Godavari (KG) basin. The role of complex geology in attenuating the seismic signal is also studied by generating synthetic seismic data for different geological models and by computing the corresponding attenuation. It has been found that the Q−1 obtained from the field seismic data compares well with the Q−1 computed for a simple layered geological model. The results indicate that the Q−1 (0.0029) from field seismic data is ∼4.3 times lower than Q−1 (0.0123–0.0125) obtained from the sonic data, implying that the thickness of the gas hydrate layer in the KG basin is not sufficient enough to average the bulk properties. Our results also indicate that there could be substantial contribution of the pore scale interaction to the observed attenuation.

LET dependence of bubbles evaporation pulses in superheated emulsion detectors

Superheated emulsion detectors are suspensions of metastable liquid droplets in a compliant inert medium. Upon interaction with ionizing radiation, the droplets evaporate, generating visible bubbles. Bubble expansion associated with the boiling of the droplets is accompanied by pressure pulses in both the sonic and ultrasonic frequency range. In this work, we analyzed the signal generated by bubble evaporation in the frequency and time domain. We used octafluoropropane (R-218) based emulsions, sensitive to both photons and neutrons. The frequency content of the detected pulses appears to extend well into the hundreds of kHz, beyond the range used in commercial devices to count bubbles as they are formed (typically 1–10kHz). Kilohertz components characterize the early part of the waveforms, potentially containing information about the energetics of the explosive bubble initial growth phase. The power spectral density of the acoustic signal produced by neutron-induced evaporation shows a characteristic frequency pattern in the 200–400kHz range, which is not observed when bubbles evaporate upon gamma ray-induced irradiation. For practical applications, detection of ultrasonic pulses associated with the boiling of the superheated drops can be exploited as a fast readout method, negligibly affected by mechanical ambient noise.

A new laboratory technique for determining the compressional wave properties of marine sediments at sonic frequencies and in situ pressures

ABSTRACTWe describe a new laboratory technique for measuring the compressional wave velocity and attenuation of jacketed samples of unconsolidated marine sediments within the acoustic (sonic) frequency range 1–10 kHz and at elevated differential (confining – pore) pressures up to 2.413 MPa (350 psi). The method is particularly well suited to attenuation studies because the large sample length (up to 0.6 m long, diameter 0.069 m) is equivalent to about one wavelength, thus giving representative bulk values for heterogeneous samples. Placing a sediment sample in a water‐filled, thick‐walled, stainless steel Pulse Tube causes the spectrum of a broadband acoustic pulse to be modified into a decaying series of maxima and minima, from which the Stoneley and compressional wave, velocity and attenuation of the sample can be determined. Experiments show that PVC and copper jackets have a negligible effect on the measured values of sediment velocity and attenuation, which are accurate to better than ± 1.5% for velocity and up to ± 5% for attenuation. Pulse Tube velocity and attenuation values for sand and silty‐clay samples agree well with published data for similar sediments, adjusted for pressure, temperature, salinity and frequency using standard equations. Attenuation in sand decreases with pressure to small values below Q−1 = 0.01 (Q greater than 100) for differential pressures over 1.5 MPa, equivalent to sub‐seafloor depths of about 150 m. By contrast, attenuation in silty clay shows little pressure dependence and intermediate Q−1 values between 0.0206–0.0235 (Q = 49–43). The attenuation results fill a notable gap in the grain size range of published data sets. Overall, we show that the Pulse Tube method gives reliable acoustic velocity and attenuation results for typical marine sediments.

Nondestructive Investigation of Stress-Induced Damage in Concrete

The changes in the sonic surface wave velocity of concrete under stress were investigated in this paper. Surface wave velocities at sonic frequency range were measured on a prismatic concrete specimen undergoing several cycles of uniaxial compression. The loading was applied (or removed) gradually in predefined small steps (stress-controlled). The surface wave velocity was measured at every load step during both loading and unloading phases. Acoustic Emission (AE) test was conducted simultaneously to monitor the microcracking activities at different levels of loading. It was found that the sonic surface wave velocity is highly stress dependent and the velocity-stress relationship follows a particular trend. The observed trend could be explained by a combination of acoustoelasticity and microcracking theories, each valid over a certain range of applied stresses. Having measured the velocities while unloading, when the material suffers no further damage, the effect of stress and damage could be differentiated. The slope of the velocity-stress curves over the elastic region was calculated for different load cycles. This quantity was normalized to yield a dimensionless nonlinear parameter. This parameter generally increases with the level of induced damage in concrete.

Sonic to ultrasonic Q of sandstones and limestones: Laboratory measurements at in situ pressures

Laboratory measurements of the attenuation and velocity dispersion of compressional and shear waves at appropriate frequencies, pressures, and temperatures can aid interpretation of seismic and well-log surveys as well as indicate absorption mechanisms in rocks. Construction and calibration of resonant-bar equipment was used to measure velocities and attenuations of standing shear and extensional waves in copper-jacketed right cylinders of rocks ([Formula: see text] in length, [Formula: see text] in diameter) in the sonic frequency range and at differential pressures up to [Formula: see text]. We also measured ultrasonic velocities and attenuations of compressional and shear waves in [Formula: see text]-diameter samples of the rocks at identical pressures. Extensional-mode velocities determined from the resonant bar are systematically too low, yielding unreliable Poisson’s ratios. Poisson’s ratios determined from the ultrasonic data are frequency corrected and used to calculate thesonic-frequency compressional-wave velocities and attenuations from the shear- and extensional-mode data. We calculate the bulk-modulus loss. The accuracies of attenuation data (expressed as [Formula: see text], where [Formula: see text] is the quality factor) are [Formula: see text] for compressional and shear waves at ultrasonic frequency, [Formula: see text] for shear waves, and [Formula: see text] for compressional waves at sonic frequency. Example sonic-frequency data show that the energy absorption in a limestone is small ([Formula: see text] greater than 200 and stress independent) and is primarily due to poroelasticity, whereas that in the two sandstones is variable in magnitude ([Formula: see text] ranges from less than 50 to greater than 300, at reservoir pressures) and arises from a combination of poroelasticity and viscoelasticity. A graph of compressional-wave attenuation versus compressional-wave velocity at reservoir pressures differentiates high-permeability ([Formula: see text], [Formula: see text]) brine-saturated sandstones from low-permeability ([Formula: see text], [Formula: see text]) sandstones and shales.

Effect of the magnetic state on the damping properties of iron and nickel alloys

The dependences of the ΔEeffect and internal friction on the magnetic field have been investigated upon the magnetization and magnetization reversal of some polycrystalline ferromagnetic materials with different properties. It has been shown that for all the materials that have been investigated there is characteristic a nonmonotonic dependence of the magnitude of internal friction on the magnetic field both for the magnetization curves and for the major hysteresis loops. It is shown that in the sonic frequency range of elastic vibrations the basic mechanism of the formation of the magnetic peaks of internal friction in the materials investigated is magnetostrictive; the damping depends simultaneously on the instantaneous values of magnetostriction and magnetostrictive sensitivity.

Multicoaxial cylindrical inclusions in locally resonant phononic crystals

It is known that the transmission spectrum of the so-called locally resonant phononic crystal can exhibit absolute sharp dips in the sonic frequency range due to the resonance scattering of elastic waves. In this paper, we study theoretically, using a finite difference time domain method, the propagation of acoustic waves through a two-dimensional locally resonant crystal in which the matrix is a fluid (such as water) instead of being a solid as in most of the previous papers. The transmission is shown to be dependent upon the fluid or solid nature of the matrix as well as upon the nature of the coating material in contact with the matrix. The other main purpose of this paper is to consider inclusions constituted by coaxial cylindrical multilayers consisting of several alternate shells of a soft material (such as a soft rubber) and a hard material (such as steel). With respect to the usual case of a hard core coated with a soft rubber, the transmission spectrum can exhibit in the same frequency range several peaks instead of one. If two or more phononic crystals are associated together, we find that the structure displays all the zeros of transmission resulting from each individual crystal. Moreover, we show that it is possible to overlap the dips by an appropriate combination of phononic crystals and create a larger acoustic stop band.

Seismic attenuation from VSP data in methane hydrate-bearing sediments

Recent seismic surveys have shown that the presence of methane hydrate (MH) in sediments has significant influence on seismic attenuation. I have used vertical seismic profile (VSP) data from a Nankai Trough exploratory well, offshore Tokai in central Japan, to estimate compressional attenuation in MH-bearing sediments at seismic frequencies of 30–110 Hz. The use of two different measurement methods (spectral ratio and centroid frequency shift methods) provides an opportunity to validate the attenuation measurements. The sensitivity of attenuation analyses to different depth intervals, borehole irregularities, and different frequency ranges was also examined to validate the stability of attenuation estimation. I found no significant compressional attenuation in MH-bearing sediments at seismic frequencies. Macroscopically, the peaks of highest attenuation in the seismic frequency range correspond to low-saturation gas zones. In contrast, high compressional attenuation zones in the sonic frequency range (10–20 kHz) are associated with the presence of methane hydrates at the same well locations. Thus, this study demonstrated the frequency-dependence of attenuation in MH-bearing sediments; MH-bearing sediments cause attenuation in the sonic frequency range rather than the seismic frequency range. As a possible reason why seismic frequencies in the 30–110 Hz range were not affected in MH-bearing sediments, I point out the effect of thin layering of MH-bearing zones.

Seismic wave attenuation in methane hydrate‐bearing sediments: Vertical seismic profiling data from the Nankai Trough exploratory well, offshore Tokai, central Japan

Data from two vertical seismic profiles (VSPs) from the Nankai Trough exploratory well, offshore Tokai, central Japan, are used to estimate compressional attenuation in methane hydrate (MH)‐bearing sediments at seismic frequencies of 30–110 Hz. We compare spectral ratio and centroid frequency shift methods for measuring attenuation. To isolate intrinsic attenuation from total attenuation, attenuation is computed from multiples using one‐dimensional synthetic VSP data from sonic and density logs. The use of two different measurement methods and two VSPs recorded at just 100 m separation provides an opportunity to validate the attenuation measurements. No significant compressional attenuation was observed in MH‐bearing sediments at seismic frequencies. Macroscopically, the peaks of highest attenuation in the seismic frequency range correspond to low‐saturation gas zones. In contrast, high compressional attenuation zones in the sonic frequency range (10–20 kHz) are affected by the presence of methane hydrates in the same well locations. Thus this study demonstrated the frequency dependence of attenuation in MH‐bearing sediments; MH‐bearing sediments cause attenuation in the sonic frequency range rather than the seismic frequency range.

Modeling of acoustic wave dissipation in gas hydrate–bearing sediments

Recent sonic and seismic data in gas hydrate–bearing sediments have indicated strong waveform attenuation associated with a velocity increase, in apparent contradiction with conventional wave propagation theory. Understanding the reasons for such energy dissipation could help constrain the distribution and the amounts of gas hydrate worldwide from the identification of low amplitudes in seismic surveys. A review of existing models for wave propagation in frozen porous media, all based on Biot's theory, shows that previous formulations fail to predict any significant attenuation with increasing hydrate content. By adding physically based components to these models, such as cementation by elastic shear coupling, friction between the solid phases, and squirt flow, we are able to predict an attenuation increase associated with gas hydrate formation. The results of the model agree well with the sonic logging data recorded in the Mallik 5L‐38 Gas Hydrate Research Well. Cementation between gas hydrate and the sediment grains is responsible for the increase in shear velocity. The primary mode of energy dissipation is found to be friction between gas hydrate and the sediment matrix, combined with an absence of inertial coupling between gas hydrate and the pore fluid. These results predict similar attenuation increase in hydrate‐bearing formations over most of the sonic and seismic frequency range.

The Affect of Selection in Digital Sound Art

The Affect of Selection in Digital Sound Art

Locally resonant sonic materials

We have fabricated a new type of composite which displays localized sonic resonances at ∼350– 2000 Hz with a microstructure size in the millimeter to centimeter range. Around the resonance frequencies the composite behaves as a material with effective negative elastic constants and as a total wave reflector—a 2 cm slab of this material is shown to break the conventional mass-law of sound transmission by order(s) of magnitude. When the microstructure is periodic, our composites exhibit large elastic wave band gaps at the sonic frequency range, with a lattice constant order(s) of magnitude smaller than the corresponding sonic wavelength in air. Good agreement is obtained between theory and experiment.

Scale-up of sonic energy for a major industrial application: ash conditioning for power utilities that use fluidized bed combustion

The paper describes a new, powerful, patented piece of sonic equipment that operates in the low sonic frequency range, at 104 Hz, with nominal power of 75 kW. It has been tested for both physical and chemical sonic effects. A large-scale industrial application is described — the conditioning and pacification of ash from utility coal combustion by fluidized bed combustion. A variety of additional applications is suggested, most of which have been briefly tested.

Effects of heterogeneities and anisotropy on sonic and ultrasonic attenuation in rocks

We compare the attenuation obtained by the resonant bar technique in the sonic frequency range (3–10 kHz) with that obtained by the pulse transmission technique in the ultrasonic frequency range (500 kHz) on a set of 30 rocks, including sandstones and limestones. The sonic and ultrasonic measurements were performed under high effective pressure on adjacent water‐saturated samples from each rock block. Compressional ultrasonic attenuation was typically larger than extensional sonic attenuation, particularly in limestones. This is attributed to the presence of density heterogeneities, that can be seen on X‐ray scanner imagery. Heterogeneities at the scale of the ultrasonic wavelength produce diffraction of the waves, and as a consequence, high attenuation values. At ultrasonic frequencies, large apparent shear attenuation values, compared to compressional attenuation values, are explained by shear wave splitting.

Sonic properties of rocks under confining pressure using the resonant bar technique

This paper presents in detail the resonant bar technique used to measure acoustic properties of materials in the sonic frequency range (≃5–20 kHz). Measurements are corrected for the effects of added mass and jacketing; extrinsic effects such as the sample diameter or the dispersion at higher frequencies can mask intrinsic properties of material and are analyzed here. When this technique is used on porous saturated media such as rocks, it is important to avoid the “Biot–Gardner–White” effect; this intrinsic effect can lead to erroneous high attenuations in unjacketed saturated samples. Experimental evidence of its occurrence on water-saturated rods is presented. Experimental results of velocity and attenuation obtained on various rock types such as limestones and sandstones show the drastic sensitivity of these measurements to effective pressure. Hertz’s theory can be applied to describe the behavior of under-consolidated sandstones. Under high confining pressure, sonic attenuation in water-saturated limestone samples is found to be very low (Q⩾100); attenuation in sandstones is always low (Q⩾50), except for some shaly sandstones.

Ultrasonic characteristics of a rock mass

A programme aimed at the in-situ assessment of rock properties and rock condition has been undertaken at the Julius Kruttschnitt Mineral Research Centre of the University of Queensland. The project aims to quantify rock mass parameters and to use them in a model of blasting to predict and control fragmentation. A technique for characterization of a rock mass utilizing acoustic data obtained from test or production boreholes was investigated as part of the programme. The system is a cross-hole acoustic system which uses wave propagation velocities and the attenuation parameter, Q (as estimated from a measurement of the change in pulse shape during propagation) to asses the rock mass condition. This system is a modification of the ultrasonic stress monitoring device (USMD) developed by Gladwin [5] in which a magnetostrictive transducer, mechanically clamped in an NX borehole is used to produced ultrasonic pulses of approximately 37.5 kHz. Pulse transmission times to detectors clamped at measured depths are used to produce a velocity profile for distances of up to 15 m from the source hole. The viability of the technique and the required instrument specifications, have been studied in a series of field experiments, which indicate good agreement between structural core log data and pulse rise time. Characterization of the state of fracture of a rock mass is being carried out at several sites with markedly different geological environments. These sites include a high grade open cut hematite mine, an open cut coal mine, an underground dolomitic copper ore body, and an underground lead-zinc ore body. The ultrasonic technique is being supplemented by studies in the sonic frequency range using small explosive charges as a acoustic sources. A comparison between the two sets of data will be made for both velocity and Q measurements for the preliminary field experimentation.

Measuring system for complex shear modulus of liquids using torsionally vibrating quartz crystals

In rheology, torsionally vibrating quartz crystals are in use to determine dynamic shear moduli of liquids in the sonic and ultrasonic frequency range. A computer controlled measuring system using such crystals is described. The main advantages of this system are high measuring speed with respect to the manual AC bridge method and on-line data reduction. As an illustration measurements of a solution of polystyrene in toluene in the 10-100 kHz range are presented.