Ultrasonic Pulse Transmission Research Articles

Effects of Humidity on Mycelium-Based Leather.

Leather is a product that has been used for millennia. While it is a natural material, its production raises serious environmental and ethical concerns. To mitigate those, the engineering of sustainable biobased leather substitutes has become a trend over the past few years. Among the biobased materials, mycelium, the fungal "root" of a mushroom, is one of the promising alternatives to animal leather, as a material with tunable physicomechanical properties. Understanding the effect of humidity on mycelium-based leather material properties is essential to the production of durable, competitive, and sustainable leather products. To this end, we measured the water sorption isotherms on several samples of mycelium-based leather materials and investigated the effects of water sorption on their elastic properties. The ultrasonic pulse transmission method was used to measure the wave speed through the materials while measuring their sorption isotherms at different humidity levels. Additionally, the material's properties were mechanically tested by performing uniaxial tensile tests under ambient and immersed conditions. An overall reduction in elastic moduli was observed during both absorption and immersion. The changes in the measured longitudinal modulus during water sorption reveal changes in the elasticity of the test materials. The observed irreversible variation of the longitudinal modulus during the initial water sorption can be related to the material production process and the presence of various additives that affect the mechanical properties of the leather materials. Our results presented here should be of interest to material science experts developing a new generation of sustainable leather products.

Experimental investigation of pore-filling substitution effect on frequency-dependent elastic moduli of Berea sandstone

SUMMARY Based on both forced oscillation and ultrasonic pulse transmission methods, we investigated solid pore infill influences on rock elastic moduli in a broad frequency range $[ {1 - 3000,\,\,{{10}^6}} ]$ Hz for different differential pressures. For a Berea sandstone sample, filled sequentially by solid (${22\,\,^{\rm{o}}}{\rm{C}}$), quasi-solid (${26\,\,^{\rm{o}}}{\rm{C}}$) and liquid (${34\,\,^{\rm{o}}}{\rm{C}}$) octadecane, a frequency-dependence was found for the Poisson's ratio, Young's modulus and bulk modulus, nevertheless, these elastic parameters were strongly suppressed by increasing pressures. Experimental measurements showed that shear wave velocity and modulus of solid-octadecane-filled samples are significantly larger than those of the dry and liquid-octadecane-filled ones, implying the potential stiffening effects related to solid infill in compliant pores. A three porosity structure model, which describes the solid stiffening effects related to equant, compliant and the intermediate pores with aspect ratios larger than those of compliant pores but much less than those of stiff pores, was used to compare against the experimentally measured elastic properties for octadecane pore infill, together with several other fluid/solid substitution theories. The agreement between experimental measurements and theoretical predictions is reasonably good for the sandstone tested, providing that the three porosity model can be applied for pressure- and frequency-dependent elastic moduli estimations for a viscoelastic pore-infill-saturated sandstone. Evaluating the combined squirt flow mechanism responsible for the observed moduli dispersion and attenuation is of great importance to reduce potential errors in seismic AVO inversion and 4-D seismic monitoring of gas-hydrate or bitumen-saturated reservoir, especially for reservoir rocks with complex microstructures and heterogeneous pore types.

Anisotropy and Energy Evolution Characteristics of Shales: A Case Study of the Longmaxi Formation in Southern Sichuan Basin, China

To obtain the influence of anisotropy and energy evolution characteristics on wellbore stability, the acoustic and mechanical anisotropy characteristics of shales are studied through various experiments, including scanning electron microscopy, ultrasonic pulse transmission, and uniaxial compression experiments, with the Longmaxi Formation shale in the southern area of the Sichuan Basin as the research object. The energy evolution characteristics of the Longmaxi Formation shale under different bedding angles are analyzed. The influence of anisotropy on the wellbore stability of shale formation is discussed on this basis. The results show that the acoustic and mechanical parameters, failure mode, and energy evolution characteristics of shale have significant anisotropy. Furthermore, the P-wave and S-wave time differences decrease with an increase in bedding angle. The compressive strength and Poisson’s ratio decrease first and then increase with an increase in bedding angle. Meanwhile, the elastic modulus gradually increases with an increase in bedding angle. Rock samples with different bedding angles show diverse failure modes in mechanical tests, including splitting, shear, and shear-splitting failure. The total energy and elastic energy decrease first and then increase with an increase in bedding angle. Finally, the formation anisotropy affects the wellbore stability: the higher the formation anisotropy, the more vulnerable is the wellbore to instability.

Impact of drying-wetting cycles on the small strain behaviour of compacted clay

Small strain shear modulus (Gmax) is an important parameter for assessing the performance of compacted soils that underlie typical transport infrastructure assets such as railway tracks. This is particularly important when considering changes in climate patterns, which are expected to yield larger seasonal soil-atmosphere moisture fluctuations. This in turn results in the progressive variation of the small strain properties of compacted soils during their service life (i.e. drying and wetting). In this study, the small strain shear behaviour was evaluated for an intermediate plasticity clay (i.e. kaolin) in a series of drying and wetting cycles. Four different dying and wetting boundaries were considered to explore a wide range of moisture amplitudes during 10 drying-wetting cycles. Drying and wetting was controlled using gravimetric water content in order to mimic realistic field conditions typically observed at substructure level. An ultrasonic pulse transmission method was used to capture the change in small strain stiffness and volume at discrete points during the drying-wetting cycles. The results reveal clear distinctions in behaviour for all four boundaries considered, with wetting boundaries having the greatest influence on behaviour. In this instance, specimens brought to full saturation during wetting exhibited an increase in the small strain shear modulus during progressive drying-wetting cycles. However, a reduction was observed when the wetting boundary was restricted to the compacted state. Measured volume changes were also in agreement with these findings, however there was some evidence of volume increase when drying to residual conditions. The results suggest that this is associated with the formation of the partial pendular state where a loss of capillary contacts between particles occurs. Furthermore, when all data for 10 drying-wetting cycles is plotted in the e-Gmax space, a linear relationship is observed for different constant water content levels. Remarkably, this trend is shown to be independent of the boundary conditions considered in this study or number of drying-wetting cycles.

Influence of Nb2O5 Additive on Elastic and Dielectric Properties of NiCuZn Ferrites

The influence of Nb2O5 additive on elastic and dielectric properties of NiZnCu ferrite is reported. The longitudinal and shear wave velocities were measured by ultrasonic pulse transmission method. The elastic constants increased as the Nb2O5 contents increased. The dielectric parameters such as dielectric constant (ɛ′) and dielectric loss tangents as a function of frequency and Nb2O5 additive composition for all samples at room temperature. The variations in the dielectric constant (ɛ′) and dielectric loss tangents values were explained using Maxwell–Wagner interfacial polarization according to Koops phenomenological theory. AC conductivity was increased with an increase in the frequency. A reduction in AC conductivity with Nb2O5 additive is reported.

Acoustic Assessment of Multiscale Porous Lime-Cement Mortars

Noise pollution is an issue of high concern in urban environments and current standards and regulations trend to increase acoustic insulation requirements concerning airborne noise control. The design and development of novel building materials with enhanced acoustic performance is an efficient solution to mitigate this problem. Their application as renders and plasters can improve the acoustic conditions of existing and brand-new buildings. This paper reports the acoustic performance of eleven multiscale porous lime-cement mortars (MP-LCM) with two types of fibers (cellulose and polypropylene), gap-graded sand, and three lightweight aggregates (expanded clay, perlite, and vermiculite). Gap-graded sand was replaced by 25 and 50% of lightweight aggregates. A volume of 1.5% and 3% of cellulose fibers were added. The experimental study involved a physical characterization of properties related to mortar porous microstructure, such as apparent density, open porosity accessible to water, capillarity absorption, and water vapor permeability. Mechanical properties, such as Young's modulus, compressibility modulus, and Poisson's ratio were evaluated with ultrasonic pulse transmission tests. Acoustic properties, such as acoustic absorption coefficient and global index of airborne noise transmission, were measured using reduced-scale laboratory tests. The influence of mortar composition and the effects of mass, homogeneity, and stiffness on acoustic properties was assessed. Mortars with lower density, lower vapor permeability, larger open porosity, and higher Young's and compressibility modulus showed an increase in sound insulation. The incorporation of lightweight aggregates increased sound insulation by up to 38% compared to the gap-graded sand reference mixture. Fibers slightly improved sound insulation, although a small fraction of cellulose fibers can quadruplicate noise absorption. The roughness of the exposed surface also affected sound transmission loss. A semi-quantitative multiscale model for acoustic performance, considering paste thickness, active void size, and connectivity of paste pores as key parameters, was proposed. It was observed that MP-LCM with enhanced sound insulation, slightly reduced sound absorption.

Effect of microscopic pore structures on ultrasonic velocity in tight sandstone with different fluid saturation

Microcosmic details of pore structure are the essential factors affecting the elastic properties of tight sandstone reservoirs, while the relationships in between are still incompletely clear due to the fact that quantitative or semi-quantitative experiments are hard to achieve. Here, three sets of tight sandstone samples from the Junggar Basin are selected elaborately based on casting thin sections, XRD detection, and petro-physical measurement, and each set is characterized by a single varied microcosmic factor (pore connectedness, pore type, and grain size) of the pore structure. An ultrasonic pulse transmission technique is conducted to study the response of elastic properties to the varied microcosmic details of pore structure in the situation of different pore fluid (gas, brine, and oil) saturation and confining pressure. Observations show samples with less connectedness, inter-granular dominant pores, and smaller grain size showed greater velocities in normal conditions. V p is more sensitive to the variations of pore type, while V s is more sensitive to the variations of grain size. Samples with better connectedness at fluid saturation (oil or brine) show greater sensitivity to the confining pressure than those with gas saturation with a growth rate of 6.9% to 11.9%, and the sensitivity is more likely controlled by connectedness. The pore types (inter-granular or intra-granular) can be distinguished by the sensitivity of velocities to the variation of pore fluid at high confining pressure (> 60 MPa). The samples with small grain sizes tend to be more sensitive to the variations of confining pressure. With this knowledge, we can semi-quantitatively distinguish the complex pore structures with different fluids by the variation of elastic properties, which can help improve the precision of seismic reservoir prediction for tight sandstone reservoirs.

Vertical velocity at hydrostatic and anisotropic stresses

Sonic and dipole wireline tools measure Vp and Vs along the vertical direction. The state of stress in the subsurface is predominantly anisotropic, while most laboratory experiments measuring the dynamic elastic properties are conducted under hydrostatic stress. The question we ask is whether such laboratory experiments provide the velocities that are close to those measured in the vertical wellbore where the stresses are anisotropic. To address this question, we conducted ultrasonic pulse transmission experiments on several room-dry rock samples. The comparison was made between the P- and S-wave velocities obtained at pure hydrostatic loading conditions and those at a smaller hydrostatic stress with added axial stress, so that the total stress along the axis of a cylindrical plug was the same as under pure hydrostatic loading. These differences were significant in the extreme case of only 1 MPa hydrostatic confining stress with the axial stress increasing up to 40 MPa. However, as the hydrostatic (confining) stress increased, the differences between the velocities along the axis of the sample became smaller and smaller. For example, at 1 MPa confining and 30 MPa axial stress, the relative difference in Vp was about 10%, while that in Vs was about 20%. However, at 10 MPa confining stress, these differences became about 3% and 6%, respectively, and further decreased as the confining stress increased. This means that even at strong in-situ contrasts between the vertical and horizontal stresses, the results of laboratory hydrostatic experiments can be used for in-situ velocity estimates. These results also appear to be consistent with a theoretical model that predicts the directional velocities at any triaxial stress conditions from those measured versus hydrostatic stress.

Enhanced acoustic properties of concrete composites comprising modified waste sheep wool fibers

Sheep wool is an environmentally friendly, renewable, and entirely recyclable resource that satisfies the standards of green building components. Consequently, it is increasingly employed in building material technology. The sound absorption characteristics of sheep wool render it a satisfactory building insulation material with desirable acoustic properties. This study investigates the effect of waste sheep wool fiber (WF) and modified WFs (MWF) on the acoustic and mechanical properties of concrete. Plain concrete and concrete mixtures containing 0.5–2.5% WF and MWF were tested for compressive strength, modulus of elasticity (MOE), ultrasonic pulse velocity, sound absorption, and transmission loss. The addition of WFs to concrete mixtures slightly reduced the compressive strength and MOE values. However, it significantly improved the sound insulation and noise reduction behavior of concrete specimens, with sound absorption coefficients of 0.66 and 0.75 for mixtures containing 2.5% WF and MWF, respectively, at a frequency of 2000 Hz. In general, the addition of WFs to concrete composites improved their overall acoustic qualities. The findings showed that sheep wool waste, as a sound insulation material, has acoustical properties similar to those of polymeric-based fibers, with the added advantages of being environmentally friendly, affordable, biodegradable, and abundant.

Evaluation of the energy storage capacity of Phase Change Material cement-lime mortars by using heat flux meters and ultrasonic pulse transmission

Materials with high energy storage capacity can enhance energy efficiency of buildings further than thermal insulation alone. The use of microencapsulated paraffin wax Phase Change Materials (PCM) in cement-lime mortars with cellulose fibres and lightweight aggregates (LWA) is a promising solution for this purpose. In this study, experimental techniques as flux heat meters and ultrasonic pulse transmission are used to evaluate the thermal performance and energy storage capacity of five cement-lime mortars with 20% of PCM, cellulose fibres and LWA (perlite) under different thermal conditions. A climatic chamber was used to simulate heating and cooling on one side of a sample plate of each mortar type, while the other side remained at lab conditions. Sample plates were instrumented with temperature-humidity sensors, heat flux meter plates and Ultrasonic (US) pulse transducers. US attenuation coefficient was used to identify the phase change PCM from solid to liquid and vice versa, during heating and cooling. The Heat flux difference between both sides of the plates was also measured during heating and cooling cycles. The specific enthalpy (energy storage capacity) of the mortars was calculated for heating and cooling cycles. Mixtures with LWA and PCM showed the best thermal performance achieving larger heat storage capacity than mortars with fibres or the combination of both LWA and fibres.

Enhanced Acoustic Properties of a Novel Prepacked Aggregates Concrete Reinforced with Waste Polypropylene Fibers.

This research aimed to investigate the performance of prepacked aggregates fiber-reinforced concrete (PAFRC) with adequate acoustic characteristics for various applications. PAFRC is a newly developed concrete made by arranging and packing aggregates and short fibers in predetermined formworks, then inserting a grout mixture into the voids amongst the aggregate particles using a pump or gravity mechanism. After a one-year curing period, the effects of utilizing waste polypropylene (PP) fibers on the strength and acoustic characteristics of PAFRC mixes were examined. Compressive and tensile strengths, ultrasonic pulse velocity (UPV), sound absorption, and transmission loss were investigated on plain concrete and PAFRC mixtures comprising 0–1% PP fibers. The results revealed that the use of PP fibers slightly decreased the compressive strength and UPV of PAFRC mixes. The inclusion of waste PP fibers also significantly increased the tensile strength and sound insulation coefficient of PAFRC mixes, especially at higher fiber dosages. In the medium-to-high frequency ranges, more than 60% acoustic absorption coefficient was observed, indicating that PAFRC specimens have good sound insulation properties.

Durability and Safety Performance of Pavements with Added Photocatalysts

The use of photocatalysts to enhance the performance of construction materials with large surfaces exposed to sunlight has become an increasingly common practice in recent decades. Although construction material durability is of crucial importance and is extensively studied when incorporating new additions, very few studies have specifically addressed the effects when adding photocatalysts. This paper discusses the effect of TiO2-based photocatalysts on pavement durability (porosity, time of transmission of ultrasonic pulses, freeze-thaw resistance and capillary water absorption) and safety (slip resistance and roughness) by comparison of commercial photocatalytic materials of different families and twin materials without the photocatalyst added. The analysis covers concrete tile pavements and porous asphalt treated with photocatalysts in the form of sprayed emulsions, slurry admixtures or built-in during casting. The findings show that changes in the properties of a construction material induced by photocatalytic functionality depend primarily on the porous structure of the matrix and the properties of the resulting photocatalytic surface.

Ultrasonic S-wave responses of single rock joints filled with wet bentonite clay

Clay minerals are prevalent in rock discontinuities and have significant effects on mechanical, hydraulic and seismic properties of rock masses. Understanding seismic behaviours across individual clay-rich rock joints is of great importance in the fields of geology and earth sciences. However, the wave responses of individual clay-rich rock joints have not been well understood until now. This paper reports a laboratory investigation of ultrasonic S-wave propagation and attenuation across single rock joints filled with bentonite clays with varying degree of water saturation. In this study, a series of acoustic measurements were conducted on specimens of the bentonite clay-filled rock joint using a self-developed ultrasonic pulse-transmission test system that equipped with a S-wave transducer pair with a dominant frequency of 250 kHz. Based on the obtained laboratory data, the wave velocity, transmission ratio and the time-frequency-energy distribution of the S-waves transmitted through the bentonite clay-filled joint were calculated and evaluated. The experimental results show that the degree of water saturation of the bentonite clay greatly affects S-wave responses of the filled rock joint. In particular, an increase in the degree of saturation causes a nonlinear decrease in S-wave velocity. In addition, as the water saturation of the bentonite clay increases, the wave attenuation decreases; the minimum wave attenuation is reached at a saturation degree of 71.4% and then the attenuation increases slightly. Additionally, with the increase of the water saturation, the magnitudes of the S-wave energy transmitted across the bentonite clay-filled joint firstly increases and then decreases. The S-wave energy is mostly stored in the frequency range of 150 - 300 kHz regardless of the degree of water saturation of the bentonite clay. This finding indicates that the frequency partition of the transmitted S-waves rarely changes with the changing water saturation. The present work could not only compensate for the lack of laboratory-based research on wave behaviours across clay-rich rock joints but also provides insights into the interpretation of acoustic data from field tests for detecting, characterizing and monitoring rock discontinuities.

A comparative study of different concentrations of (Co/Ni/Cu) effects on elastic properties of Li–Mn ferrite employing IR spectroscopy and ultrasonic measurement

Three series of divalent ions (Co2+/Ni2+/Cu2+) substituted into lithium-manganese ferrites were synthesized using a typical ceramic technique. Two different methods were used to investigate their elastic properties. Infrared (IR) spectroscopy showed two essential bands referring to the tetrahedral ‘υA’ and the octahedral ‘υB’ sites. The force constant, elastic wave velocity and elastic moduli of all specimens have been calculated from the results of IR spectroscopy. Using the ultrasonic pulse transmission (UPT) technique, the longitudinal and shear wave velocities were measured. Using these values; bulk modulus (B), rigidity modulus (G), Young's modulus (E), and Poisson ratio (σ) were determined. In comparison, the elastic moduli resulting from IR spectroscopy results were larger than those obtained from UPT measurements. Because the present ferrite systems are porous, the elastic moduli of the compositions from UPT have been adjusted to zero porosity by two models. The values of the adjusted elastic moduli have been shown to have the same trend as those of the uncorrected elastic moduli. Elastic parameters have generally improved dramatically for Li–Mn–Co ferrite and Li–Mn–Ni ferrite compared to Li–Mn–Cu ferrite. Higher elastic moduli values have been obtained in Li–Mn–Co spinel ferrites, suggesting that such materials are ideal for use in core shapes. Two methods were used to evaluate the Debye temperature of all compositions.

Identification of gas-liquid two-phase flow patterns in a horizontal pipe based on ultrasonic echoes and RBF neural network

This paper proposes a novel flow pattern identification method using ultrasonic echo signals within the pipe wall. A two-dimensional acoustic pressure numerical model is established to investigate the ultrasonic pulse transmission behavior between the wall-gas and wall-liquid interface. Experiments were also carried out at a horizontal air-water two-phase flow loop to measure the ultrasonic echo pulse signals of stratified flow, slug flow, and annular flow. It is interesting to find that the attenuation of the ultrasonic pulse at the wall-liquid interface is faster than the attenuation at the wall-gas interface. An RBF neural network is constructed for online flow pattern identification. The normalized envelop area and the area ratios of the echo spectrum are selected as the input parameters. The results show that the stratified flow, slug flow, and annular flow can be identified with an accuracy of 94.0%.

Finite-Element Analysis of Noise Preceding the Arrival of S-Wave in Ultrasonic Measurements of Rock Velocities.

For oil and gas seismic exploration, rock velocities are essential parameters to tease out reservoir properties from seismic data. The ultrasonic pulse transmission (UPT) method has been a gold standard to estimate reservoir rock velocities in the laboratory. Regarding the UPT method, accurate determination of the travel time of waves plays a significant role in robustly measuring rock velocities. One of the most conventional ways to obtain the travel time is through the arrival picking. However, unclear noise virtually exists preceding the arrival of S-wave interfering with this arrival picking, which, sometimes, can cause enormous errors to measured S-wave velocity. Herein, we develop a 2-D, three-component (2D-3C) finite-element modeling (FEM) algorithm aiming to interpret the noise by combining with UPT measurements. The proposed 2D-3C FEM not only can efficiently compute ultrasonic wavefield radiated by circular P- or S-wave transducers but also able to obtain synthetic waveforms in the testing of S-wave velocity where polarization directions of S-wave transducers are arranged as nonparallel. To analyze the simulated ultrasonic waveforms, we introduce frequently-used concepts of edge and direct plane waves to build elastodynamic models of the ultrasonic wavefield. Then, we compare numerical results with experimental measurements. Our 2D-3C FEM results show good agreement with experimental waveforms both in P- and S-wave velocity testings. Whereafter, we pinpoint constitutions of the noise preceding the arrival of S-wave. Comparison of numerical and experimental waveforms suggests that the edge P-wave with its reflected and converted modes partially contributes to this noise, while the rest part of the noise may stem from the effects of the compressional dipole, the couplant smeared between a transducer and a sample, and inherently parasitic longitudinal vibrations of S-wave transducers. The interpretations on this noise have the potential to benefit future design of more effective S-wave transducers.

Characterization of Engineering Elastic Parameters of Oriented Strand Board (OSB) Manufactured from Poplar (Populus deltoides) Strands Using Ultrasonic Contact Pulse Transmission

When using wood and wood-based composites, it is necessary to determine the elastic constants of these engineered materials. Oriented strand board (OSB), as structural wood based panel, plays a significant role in the building sector, but the accessibility of such elastic constants of OSB is mostly limited. For this purpose, this study aimed at determining the elastic wave velocity, stiffness and all elastic constants of OSB made from Poplar (Populus deltoides) strands using ultrasonic through–transmission technique. Laboratory OSBs with the mean density of 760 kg/m3 were made with the average strand sizes of 0.6 mm in thickness, 120 mm in length and 30 mm in width. 8 % phenol-formaldehyde (PF) resin was used with the pressing conditions of 3.43 N/mm2, 190 °C and 600 s as pressure, temperature and time of pressing, respectively. The OSBs were assumed as an orthotropic model. Three modulus of elasticity (E1, E2, and E3), three shear modulus (G12, G13 and G23), and six Poisson’s ratios (v12, v21, v13, v31, v23, v32) were calculated by longitudinal, transversal and quasi-transversal waves velocities. Ultrasonically determined stiffness coefficients of OSB were investigated by representative volume elements (RVE). Therefore, the separation of scales requirement is satisfied, and the measured velocities can be applied to determine the engineering elastic parameters of the examined OSB. The results indicate that modulus of elasticity and shear modulus are in the same order of magnitude in comparison with other references, and the values of Poisson’s ratios are valid in ultrasonic range measurement. In conclusion, the ultrasonic contact pulse transmission shows great potential to determine the characterization of elastic wave velocity, stiffness and engineering elastic parameters.

Experimental testing and ultrasonic pulse transmission technique of granite for sustainable rock testing approach at Rawang, Selangor

Advanced characterization technique which is Non-destructive Testing (NDT) technique are required to monitor the testing for physical and mechanical properties of rock. Using Non-destructive Testing technique, the information gather are much faster and easier without any disturbance to the sample test. In rock engineering, the key role in the long term stability are depending on the characteristics of rock and the rock masses. Since the finding of strength parameter are time consuming and very expensive, this research is conducted to perform experimental testing and ultrasonic pulse transmission technique on granite for a sustainable rock testing approach. Through this study, it enables to identify a simple way to predict these strength parameters especially and specifically for Unconfined Compression Strength (UCS) by using Point Load Test (PLT) and Ultrasonic Pulse Velocity (UPV) Test. From this study, the correlation can be made among UCS, point load index, and sound velocity which the empirical formula for point load and the ultrasonic pulse velocity test are UCS = 20.8(Is50) + 2.2 and UCS = 144.68Vp – 684.37 respectively. The ultrasonic pulse transmission technique methods can be used to predict the compressive strength of rock. It can be practically used in the field since the technique are portable and easy to use. By using the least-square regression method, the empirical formula formulated between UPV and UCS values signifies that the correlation coefficient (R2) obtained for the equation is 0.9692 and indicates that both variables have a good agreement relationship.

Composition Dependence of Elastic Moduli of Mixed Cobalt-Zinc Ferrites Prepared by Citrate Precursor Method

CoxZn1-xFe2O4 nanoparticles were prepared by chemical citrate precursor synthesis method. The Young’s modulus ‘E’ and the rigidity modulus ‘n’ of mixed cobalt-zinc ferrites have been determined by the ultrasonic pulse transmission technique at 1 MHz. The elastic modules of the ferrites were corrected to zero porosity using the formulae of Harselman and Fulrath. The observed variation of the elastic module with composition has been interpreted on the basis of binding forces between the atoms of the spinal lattice. A linear relationship between Debye temperature ØD and average sound velocity Vm has also been observed.

Experimental efforts to access 4D feasibility and interpretation issues of Brazilian presalt carbonate reservoirs

Brazilian presalt reservoirs comprise carbonate rocks saturated with light oil with different amounts of [Formula: see text] and excellent productivity. The occurrence of giant-size accumulations with such productivity generates the interest in production monitoring tools, such as time-lapse seismic. However, time-lapse seismic may present several challenges, such as imaging difficulties, repeatability, and detectability of small variations of reservoir properties. In addition, when assessing time-lapse seismic feasibility, the validity of Gassmann’s modeling for complex, heterogeneous carbonate rocks is arguable. Other questions include the pressure variation effects on the seismic properties of competent rocks. The effective stress is a linear combination of confining stress and pore pressure that governs the behavior of physical properties of rocks. Many applications assume that the effective stress for elastic-wave velocity is given by the difference between confining stress and pore pressure, whereas another common approach uses the Biot-Willis coefficient as a weight applied to the pore pressure to estimate the effective stress. Through a series of experiments involving ultrasonic pulse transmission on saturated core plugs in the laboratory, we verified the applicability of Gassmann’s fluid substitution and estimated the empirical effective stress coefficients related to the P- and S-wave velocities for rock samples from two offshore carbonate reservoirs from the presalt section, Santos Basin. We observed that Gassmann’s equation predicts quite well the effects of fluid replacement, and we found that the effective stress coefficient is less than one and not equal to the Biot-Willis coefficient. Moreover, there is a good agreement between the static and dynamic Biot-Willis coefficient, which is a suggestion that the presalt rocks behave as a poroelastic media. These observations suggest that more accurate time-lapse studies require the estimation of the effective stress coefficient for the particular reservoir of interest.