An analysis of seismic attenuation in random porous media

The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency.     

Ultrasonic propagation in slurries

Experimental measurements have been made of the ultrasonic velocity and attenuation in some simple suspensions of, mainly, silicon carbide in water and in ethylene glycol. These are compared with theoretical predictions based on a novel hydrodynamic model. Predicted ultrasonic velocities are in excellent agreement with the measured values. Predicted and measured ultrasonic attenuations do not agree as well. However, the suspensions give rise to excess attenuations rising to a few hundred nepers per metre and special experimental techniques were needed to measure ultrasonic properties. To predict attenuations to within, say, 20% for mixtures such as these is a major achievement.     

A model for strong attenuation and dispersion of seismic P-waves in a partially saturated fractured reservoir

In this work we interpret the data showing unusually strong velocity dispersion of P-waves (up to 30%) and attenuation in a relatively narrow frequency range. The cross-hole and VSP data were measured in a reservoir, which is in the porous zone of the Silurian Kankakee Limestone Formation formed by vertical fractures within a porous matrix saturated by oil, and gas patches. Such a medium exhibits significant attenuation due to wave-induced fluid flow across the interfaces between different types of inclusions (fractures, fluid patches) and background. Other models of intrinsic attenuation (in particular squirt flow models) cannot explain the amount of observed dispersion when using realistic rock properties. In order to interpret data in a satisfactory way we develop a superposition model for fractured porous rocks accounting also for the patchy saturation effect.     

Time-domain numerical simulations of multiple scattering to extract elastic effective wavenumbers

Elastic wave propagation is studied in a heterogeneous two-dimensional medium consisting of an elastic matrix containing randomly distributed circular elastic inclusions. The aim of this study is to determine the effective wavenumbers when the incident wavelength is similar to the radius of the inclusions. A purely numerical methodology is presented, with which the limitations usually associated with low scatterer concentrations can be avoided. The elastodynamic equations are integrated by a fourth-order time-domain numerical scheme. An immersed interface method is used to accurately discretize the interfaces on a Cartesian grid. The effective field is extracted from the simulated data, and signal-processing tools are used to obtain the complex effective wavenumbers. The numerical reference solution thus obtained can be used to check the validity of multiple scattering analytical models. The method is applied to the case of concrete. A parametric study is performed on longitudinal and transverse incident plane waves at various scatterer concentrations. The phase velocities and attenuations determined numerically are compared with predictions obtained with multiple scattering models, such as the Independent Scattering Approximation model, the Waterman–Truell model, and the more recent Conoir–Norris model.     

用非饱和三相孔弹模型研究浅层土壤中地震波的传播特性

研究浅层土壤中声波耦合的地震波的传播特性, 用于声波探雷技术的机理分析. 根据浅层土壤具有孔隙度和可压缩性的特点, 利用非饱和三相孔隙介质中的地震波模型, 研究了土壤孔隙度、含水饱和度等参数对地震波传播特性的影响. 计算结果显示: 在给定的参数条件下, 地震波的传播速度和衰减系数均随频率的增加而增加; 纵波的传播速度随孔隙度的增加而减小, 横波的传播速度随孔隙度的增加而增加; 地震波的传播特性随含水饱和度的增加变化比较复杂. 通过对计算结果与已发表实验结果的比较分析, 讨论了解析方法的可行性, 为声-地震耦合机理及其在声波探雷研究中的应用提供了一定的理论基础. 关键词： 声-地震耦合 地震波 孔隙度 声波探雷     

利用超声相干技术在室温和高压下研究几种不同性能的玻璃

 综合使用超声相干技术几种不同的测量方法，分别研究两类三种不同性能的玻璃材料，测量它们的声速和衰减在室温及高压条件下的变化规律。结果表明：两类玻璃的声速和衰减以及由此而得到的弹性常数存在较大差异。两种硅玻璃在高压下，声速随压力变化的规律相似，压力升高时，纵波速度随之单调增加，横波速度线性减少，纵波衰减也随压力升高呈增加趋势。不同的是：两种玻璃横波衰减随压力的变化规律完全相反，水白玻璃的衰减增加，窗口玻璃的减小。上述几种方法的测量结果基本一致，且在相应的压力范围内与布里渊散射的实验结果基本吻合。     

基于动电效应的震电测井方法研究进展*

与双电层和孔隙流体渗流有关的声波-电磁场耦合效应(动电耦合波)在油气储层勘探、地震电磁场等领域有着潜在应用价值。该文简述动电耦合波在理论模型以及井孔动电耦合波的实验测量、模拟计算方面的研究进展,并对油气储层测井领域进一步的动电耦合波研究进行了展望。基于动电信号的探测方法同时接收声波和电磁场两类信号,可避免单一类别信号方法的不足。实验获得了岩心的动电耦合系数,但其表征的孔隙岩石物理性质还有待进一步认识。基于耦合控制方程,开展了震电波场的计算和分析。结果表明,声源激发后,可接收到伴随声波的电磁信号和早于声波的电磁首波。这两类信号都既对影响声波特性的岩石模量、孔隙度和渗透率等参数敏感,又与电导率等岩石电学性质密切相关。非饱和岩石动电耦合波理论和基于动电耦合波的参数反演方法等问题有待进一步研究。     

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应用多光子非线性Compton散射模型,研究了Compton散射对等离子体中激光衰减特性的影响.提出了Compton散射是影响激光衰减的一个重要机制,给出了激光能量和功率衰减值的表达式,并进行了数值模拟.结果表明,Compton散射对等离子体中传输的激光能量和功率衰减值有较大影响,理论计算和数值模拟符合得很好.这也为判断等离子体中发生Compton散射提供了依据.     

Impacts of external electric fields on the permeation of glycerol and water molecules through aquaglyceroporin-7: molecular dynamics simulation approach

The European Physical Journal E - The current research numerically investigates the Marangoni convection in a cylindrical annulus filled with hybrid nanofluid saturated porous media. The interior...     

利用井中偶极弯曲波反演渗透率的影响因素及灵敏度分析

本文以各向同性饱和流体孔隙介质充液井孔中声场传播理论为基础,系统考察了影响偶极弯曲波特征的主要因素,分析了快慢地层条件下弯曲波衰减和速度对不同参数的敏感度,对比结果表明,弯曲波的速度基本不受地层渗透率的影响,其衰减对渗透率的敏感性要远高于速度。弯曲波中心频率会随着波的衰减而发生偏移,说明利用弯曲波衰减和频移特征联合反演地层渗透率是可行的。通过对比快慢地层下的弯曲波衰减和速度灵敏度曲线,发现在慢速地层中反演渗透率的结果要好于快速地层。同时,本文也指出在低孔低渗储层中,还可以考虑利用弯曲波衰减识别气层。     

Time-domain calculations of sound interactions with outdoor ground surfaces

A time-domain formulation for sound propagation in rigid-frame porous media, including waveform attenuation and dispersion, is developed. The new formulation is based on inversion of the relaxation functions from a previous model [Wilson DK, Ostashev VE, Collier SL. J Acoust Soc Am 2004;116:1889-92], thereby casting the convolution integrals in a form amenable to numerical implementation. Numerical techniques are developed that accurately implement the relaxational equations and transparently reduce to previous results in low- and high-frequency limits. The techniques are demonstrated on calculations of outdoor sound propagation involving hills, barriers, and ground surfaces with various material properties. We also compare the relaxation formulation to a widely applied phenomenological model developed by Zwikker and Kosten. The two models can be made equivalent if the resistance constant, structure constant, and compression modulus in the ZK model are allowed to be weakly frequency dependent. But if the ZK parameters are taken to be constant, as is typically the case, the relaxation model provides more accurate calculations of attenuation by acoustically soft porous materials such as snow, gravel, and forest litter.     

含少量气泡流体饱和孔隙介质中的弹性波

考虑孔隙流体中含有少量气泡,且气泡在声波作用下线性振动,研究声波在这种孔隙介质中的传播特性.本文先由流体质量守恒方程和孔隙度微分与流体压力微分的关系推导出了含有气泡形式的渗流连续性方程;在处理渗流连续性方程中的气体体积分数时间导数时,应用Commander气泡线性振动理论导出气体体积分数时间导数与流体压强时间导数的关系,进而得到了修正的Biot形式的渗流连续性方程;最后结合Biot动力学方程求得了含气泡形式的位移场方程,便可得到两类纵波及一类横波的声学特性.通过对快、慢纵波的频散、衰减及两类波引起的流体位移与固体位移关系的考察,发现少量气泡的存在对快纵波和慢纵波的传播特性影响较大.     

基于非球形雨衰模型的微波链路雨强反演方法

以T矩阵理论、Gamma谱分布为理论基础,基于Pruppacher-Beard降雨粒子模型,对OTT雨滴谱仪的Gamma谱参数历史资料与降雨强度值进行非线性拟合得到具有实地谱分布的幂律系数,建立适合于本地区的雨衰模型,提出了基于非球形雨衰模型的微波链路雨强反演方法,分析了温度对模型幂律系数的影响,并开展了15—20 GHz频段的视距微波链路与地面雨滴谱仪的同步观测降雨实验.实验结果表明:反演雨强的相关系数全部高于0.6,最高达到了0.96,RMSE最小值为0.79,累积降雨量的绝对偏差在2.47 mm以内,最小偏差仅为0.28 mm,相对误差低于1.84%.实验结果验证了基于非球形雨衰模型的微波链路雨强反演方法的有效性、准确性和适用性,对于进一步提高微波链路反演降雨精度、改善降水监测效果具有重要意义.     

Measurement of traffic noise shielding provided by buildings

This paper presents a comparison between some current prediction methods for traffic noise shielding provided by buildings and the actual measured attenuations in typical residential areas. Generally, it was found that the method developed by the Department of Environment in the UK gives a reasonably accurate prediction of attenuation by shielding in fairly simple situations. In more complex situations, and particularly where a receiving position is close to a significant shielding structure, such as building, the attenuation obtained is underpredicted by the DOE method, thus the design facade levels for the rear of a building are overpredicted; however, in some other situations, the DOE method overpredicts the attenuation obtained. The attenuations measured for individual noise events under nominally identical conditions are shown to have large variations in attenuation.     

具有不规则自由表面的粘弹性介质中声波模拟的有限差分算法

声波在具有不规则自由表面的粘弹性介质传播的数值模拟工作在地震勘探,地震预测中非常重要,特别是当模型有起伏的自由界面和较强的衰减特性时更是如此。基于镜像方法和直接方法,本文发展了一种二维有限差分算法,可以模拟不规则自由表面引起的声波散射问题。该方法将自由表面条件与速度应力方程结合求解粘弹性波动方程,在垂直和水平自由段及拐点处设置相应的边界条件。该方法假设自由表面穿过剪切应力和相应参数的网格点。为了提高计算精度,分别计算了水平和垂直方向上应力镜像值,而对质点速度,采用先水平方向后垂直方向分析进行镜像计算和更新。将粘弹性水平自由表面镜像方法和不同倾斜度平滑自由表面的改进方法的数值结果进行对比,并验证了算法的精度。     

Minimization of diffusive attenuation in T2-weighted NMR images of porous solids using turboSPI

This communication presents the results of T₂-weighted nuclear magnetic resonance imaging (MRI) of a water saturated porous volcanic rock using a fast single point imaging technique (turboSPI). Imaging porous materials with heterogeneously distributed mineral products, and air voids, using conventional imaging methods, which introduce T₂-weighting by increasing the time between the excitation and refocusing pulses, often results in high diffusive signal losses and susceptibility distortion. T₂-weighted images acquired of a water saturated porous rock using turboSPI with an effective echo time of 8.1 ms (actual inter-echo time of 0.9 ms) exhibit significantly decreased diffusive attenuation, compared to analogous images obtained with an inter-echo time of 8.1 ms.     

Compressional and shear wave properties of marine sediments: comparisons between theory and data

According to a recently developed theory of wave propagation in marine sediments, the dispersion relationships for the phase speed and attenuation of the compressional and the shear wave depend on only three macroscopic physical variables: porosity, grain size, and depth in the sediment. The dispersion relations also involve three (real) parameters, assigned fixed values, representing microscopic processes occurring at grain contacts. The dispersion relationships are compared with extensive data sets, taken from the literature, covering the four wave properties as functions of all three physical variables. With no adjustable parameters available, the theory matches accurately the trends of all the data sets. This agreement extends to the compressional and shear attenuations, in that the theory accurately traces out the lower bound to the widely distributed measured attenuations: the theory predicts the intrinsic attenuation, arising from the irreversible conversion of wave energy into heat, whereas the measurements return the effective attenuation, which includes the intrinsic attenuation plus additional sources of loss such as scattering from shell fragments and other inhomogeneities in the medium. Provided one wave or physical property is known, say the compressional speed or the porosity, all the remaining sediment properties may be reliably estimated from the theory.     

The Study of MMW and MW Attenuation Considering Multiple Scattering Effect in Sand and Dust Storms at Slant Paths

The influence of sand and dust storms on modern MMW and satellite communication systems reliability have been paid more attention to. The attenuations induced by sand and dust storms are estimated by means of Mie-theory and Rayleigh approximation, in the case of the tenuous distribution of particles. With the particle density increasing, however, these method become inadequate, the multiple scattering effects then become dominant for attenuation estimation. The attenuations considering multiple scattering effects are estimated by Monte-Carlo and four fluxes method at horizontal paths. At slant paths, based on multi-layer media model, the attenuations considering multiple scattering effects are calculated by layered Monte-Carlo method at 100, 37, 24, and 14GHz. It is shown that the multiple scattering effects should be considered at the attenuation prediction in the sand and dust storm, which the visibility is about 0.5km and smaller than 0.5km and frequency is about 20GHz. Above 30GHz, the multiple scattering effects due to sand and dust particles should be considered, as visibility is about 1km and smaller than 1km at slant paths.     

The Lattice Solid Model to Simulate the Physics of Rocks and Earthquakes: Incorporation of Friction

The particle-based lattice solid model developed to study the physics of rocks and the nonlinear dynamics of earthquakes is refined by incorporating intrinsic friction between particles. The model provides a means for studying the causes of seismic wave attenuation, as well as frictional heat generation, fault zone evolution, and localisation phenomena. A modified velocity–Verlat scheme that allows friction to be precisely modelled is developed. This is a difficult computational problem given that a discontinuity must be accurately simulated by the numerical approach (i.e., the transition from static to dynamical frictional behaviour). This is achieved using a half time step integration scheme. At each half time step, a nonlinear system is solved to compute the static frictional forces and states of touching particle-pairs. Improved efficiency is achieved by adaptively adjusting the time step increment, depending on the particle velocities in the system. The total energy is calculated and verified to remain constant to a high precision during simulations. Numerical experiments show that the model can be applied to the study of earthquake dynamics, the stick–slip instability, heat generation, and fault zone evolution. Such experiments may lead to a conclusive resolution of the heat flow paradox and improved understanding of earthquake precursory phenomena and dynamics.     

Nonlinear seismics and the acoustic action on the oil recovery from an oil pool

At the first stage of seismic action, the attenuation of acoustic waves in real (porous, creviced) rocks is always related to the energy pumping to high-frequency (ultrasonic) modes, and only at the next stage are these waves converted into chaotic thermal oscillations, so that the entire phenomenon refers to a basic problem of nonlinear seismics. Several physical phenomena related to the excitation of ultrasound and the corresponding transformations of the wave spectrum (including the dry friction in contacts, the instability of viscoelastic oscillations, the seismic energy pumping to the rotational modes, and the resonance of gas bubbles in natural oil) are considered in relation to the development of vibroseismic methods of acting upon a producing oil pool. The results of experiments on the ultrasound-stimulated water displacement of natural (gas-saturated) oil from a porous medium are presented, in which the oil recovery reached up to 90%.