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应用三维交错网格应力-速度有限差分方法,数值模拟了含有倾斜裂缝孔隙介质地层中点声源所激发的井孔声场问题.为满足薄裂缝计算需求,开发了不均匀网格有限差分算法,提高了计算精度及计算速度.利用将孔隙介质方程参数取为流体极限的办法来处理裂缝中的流体,实现了流体-孔隙介质界面处的差分方程统一,使界面处的计算更加灵活方便.在验证了方法正确性的基础上,分别考察了单裂缝宽度、裂缝带宽度、裂缝倾斜角度以及孔隙介质渗透率等参数的变化对井轴上阵列波形的影响并进行了分析.结果表明,声波经过裂缝时可能产生反射横波及斯通利波,后者随裂缝宽度的减小而减小,而前者随裂缝宽度的改变,变化不大,在裂缝很小(20μm)时依然存在;裂缝带的宽度、密度越大,反射斯通利波越强;当裂缝(裂缝带)倾斜时,反射横波消失,但反射斯通利波受裂缝倾斜角度的影响较小;渗透率的改变对斯通利波的衰减影响较为明显. 相似文献
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Analytical expressions for the borehole seismic signatures excited by an explosive source buried in an elastic half‐space 
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下载免费PDF全文 Andrei M. Ionov 《Geophysical Prospecting》2018,66(Z1):161-174
Borehole guided waves that are excited by explosive sources outside of the borehole are important for interpreting borehole seismic surveys and for rock property inversion workflows. Borehole seismograms are typically modelled using numerical methods of wave propagation. In order to benchmark such numerical algorithms and partially to interpret the results of modelling, an analytical methodology is presented here to compute synthetic seismograms. The specific setup is a wavefield emanating from a monopole point source embedded within a homogeneous elastic medium that interacts with a fluid‐filled borehole and a free surface. The methodology assumes that the wavelength of the seismic signal is much larger than the borehole radius. In this paper, it is supposed that there is no poroelastic coupling between the formation and the borehole. The total wavefield solution consists of P, PP, and PS body waves; the surface Rayleigh wave; and the low‐frequency guided Stoneley wave (often referred as the tube wave) within the borehole. In its turn, the tube wave consists of the partial responses generated by the incident P‐wave and the reflected PP and PS body waves at the borehole mouth and by the Rayleigh wave, as well as the Stoneley wave eigenmode. The Mach tube wave, which is a conic tube wave, additionally appears in the Mach cone in a slow formation with the tube‐wave velocity greater than the shear one. The conditions of appearance of the Mach wave in a slow formation are formulated. It is shown that the amplitude of the Mach tube wave strongly depends on Poisson's ratio of the slow surrounding formation. The amplitude of the Mach tube wave exponentially decreases when the source depth grows for weakly compressible elastic media with Poisson's ratio close to 0.5 (i.e., saturated clays and saturated clay soils). Asymptotic expressions are also provided to compute the wavefield amplitudes for different combinations of source depth and source‐well offset. These expressions allow an approximate solution of the wavefield to be computed much faster (within several seconds) than directly computing the implicit integrals arising from the analytical formulation. 相似文献
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This study investigates the propagation of borehole Stoneley waves across permeable structures. By modelling the structure as a zone intersecting the borehole, a simple 1D theory is formulated to treat the interaction of the Stoneley wave with the structure. This is possible because the Stoneley wave is a guided wave, with no geometric spreading as it propagates along the borehole. The interaction occurs because the zone and the surrounding formation possess different Stoneley wavenumbers. Given appropriate representations of the wavenum-ber, the theory can be applied to treat a variety of structures, including a fluid-filled fracture. Of special interest are the cases of permeable porous zones and fracture zones. The results show that, while Stoneley wave reflections are generated, strong Stoneley wave attenuation is produced across a very permeable zone. This result is particularly important in explaining the observed strong Stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory. In addition, by using a simple and sufficiently accurate theory to model the effects of the permeable zone, a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone. 相似文献
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本文利用射线展开理论、割线积分技术及留数定理,研究了裸眼井声波全波测井中纵波和斯通利波的性质。下面简要说明数值计算方法。 计算方法 考虑在无限大均匀地层中,有一充满流体的深井。在井轴上放一点状声源,则在井轴上离声源距离为z处的声压为 相似文献
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Abstract A multi-offset hydrophone vertical seismic profiling (VSP) experiment was done in a 747 m deep borehole at Nojima Hirabayashi, Hyogo prefecture, Japan. The borehole was drilled to penetrate the Nojima Fault, which was active in the 1995 Hyogo-ken Nanbu earthquake. The purpose of the hydrophone VSP is to detect subsurface permeable fractures and permeable zones and, in the present case, to estimate the permeability of the Nojima Fault. The analysis was based on a model by which tube waves are generated when incident P-waves compress the permeable fractures (or permeable zones) intersecting the borehole and a fluid in the fracture is injected into the borehole. Permeable fractures (or permeable zones) are detected at the depths of tube wave generation, and fracture permeability is calculated from the amplitude ratio of tube wave to incident P-wave. Several generations of tube waves were detected from the VSP sections. Distinct tube waves were generated at depths of the fault zone that are characterized by altered and deformed granodiorite with a fault gouge, suggesting that permeable fractures and permeable zones exist in the fault zone. Tube wave analysis shows that the permeability of the fault gouge from 624 m to 625 m is estimated to be approximately 2 × 10−12 m2 . 相似文献
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Andrei M. Ionov 《Geophysical Prospecting》2013,61(1):104-119
The dynamic response of a semi‐infinite fluid‐filled borehole embedded in an elastic half‐space under a concentrated normal surface load is analysed in the long‐wavelength limit. The solution of the problem is obtained with integral transforms in the form of a double integral with respect to the slowness and frequency. The partial P‐ and SV‐wave responses are further transformed to path integrals along Cagniard paths in the complex slowness plane. Unlike the traditional Cagniard‐de Hoop technique based on the Laplace transform of time dependence, this paper is based on the Fourier transform. The tube‐wave response is presented as a causal integral over a slowness range. The resultant representation in the time‐domain is suitable for the numerical evaluation of the complete response in the fluid‐filled borehole, especially at large distances. Asymptotic analysis of seismic phases arising in the borehole is performed on the basis of the obtained solution. The complete asymptotic wavefield consists in P‐ and SV‐waves, the Rayleigh wave and the low‐frequency Stoneley (tube) wave. Pressure synthetics obtained by the use of the asymptotic formulas are shown to be in good agreement with straightforward calculations. 相似文献
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在油、气储层的勘探和开发中观察到的一个现象是储层岩石中普遍存在孔隙和裂隙.随着近年来孔、裂隙介质弹性波动理论的进展,我们可以将此理论应用于测井技术,以此来指导从声波测井中测量孔、裂隙地层的声学参数.本文计算了孔、裂隙地层里充流体井眼中的多极子声场,分析了声场随裂隙介质的两个主要参数(即裂隙密度和裂隙纵横比)的变化特征.井孔声场的数值计算表明裂隙密度可以大幅度地降低井中声波纵、横波的波速和振幅.随着裂隙密度的增加,在测井频段内也可以看到纵、横波速的频散现象(这种频散在孔隙地层中一般是观察不到的).本文还研究了多极子模式波 (即单极的Stoneley波、伪瑞利波以及偶极的弯曲波)随裂隙参数的变化特征.结果表明,这些模式波的振幅激发和速度频散都受裂隙密度的影响.裂隙密度越高影响越大.此外,裂隙还对模式波的传播造成较大的衰减.相对裂隙密度而言,裂隙纵横比是一个频率控制参数,它控制裂隙对声场影响的频率区间.本文的分析结果对裂缝、孔隙型地层的声波测井具有指导意义. 相似文献
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The analysis of Stoneley wave propagation in a fracture is essential for the identification and evaluation of fracture parameters from the borehole Stoneley wave. Also, it is important for many geophysics considerations, e.g. for tremor and long-period events observed in volcanoes and geothermal areas. In this paper, we investigate the guided waves propagation in a fluid layer lying between two viscoelastic vertically transversely isotropic media. The viscoelastic mechanism models the attenuation due to the presence of fluid saturation in the rock. A model based on the superposition of three inhomogeneous partial plane waves: one in the fluid and two heterogeneous waves in the solid is developed. The dispersion equation is obtained for this case. A numerical solution is carried out to obtain the guided wave velocity and attenuation coefficient. The results of this investigation show that there is a strong correlation between the velocity dispersion and attenuation of Stoneley wave and the anisotropic parameters of the medium especially in a sandstone (fast) medium. 相似文献
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We study the propagation of elastic waves that are generated in a fluid‐filled borehole surrounded by a cracked transversely isotropic medium. In the model studied the anisotropy and borehole axes coincide. To obtain the effective elastic moduli of a cracked medium we have applied Hudson's theory that enables the determination of the overall properties as a function of the crack orientation in relation to the symmetry axis of the anisotropic medium. This theory takes into account the hydrodynamic mechanism of the elastic‐wave attenuation caused by fluid filtration from the cracks into a porous matrix. We have simulated the full waveforms generated by an impulse source of finite length placed on the borehole axis. The kinematic and dynamic parameters of the compressional, shear and Stoneley waves as functions of the matrix permeability, crack orientation and porosity were studied. The modelling results demonstrated the influence of the crack‐system parameters (orientation and porosity) on the velocities and amplitudes of all wave types. The horizontally orientated cracks result in maximal decrease of the elastic‐wave parameters (velocities and amplitudes). Based on the fact that the shear‐ and Stoneley‐wave velocities in a transversely isotropic medium are determined by different shear moduli, we demonstrate the feasibility of the acoustic log to identify formations with close to horizontal crack orientations. 相似文献
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A series of model experiments was performed in an ultrasonic laboratory to study the radiation of downhole sources in a variety of formations. Three models were used in the experiments. They were a Lucite model, a Lucite model with a free glass pipe in the centre, and a glass-cased soil model. In addition, a finite-difference modelling technique was used to simulate the wave propagation in these models and the results of the laboratory and numerical experiments are compared. In the Lucite borehole model the waveforms recorded in the experiment agree very well with the finite-difference synthetics. The snapshots of the wavefield from the finite-difference simulation show the radiation pattern of the P- and S-waves in the Lucite formation. These patterns are consistent with the theoretical calculations. In the Lucite model with the free glass pipe, the finite-difference synthetics are also in good agreement with the experimental observations, especially for the conical P-wave arrival. The angle between the wavefront of the conical P-wave and the borehole axis, observed from the snapshot, agrees with the theory. In the cased soil model, the arrival time of the finite-difference synthetics is in good agreement with the laboratory measurements. The relative amplitudes of the P-wave and the Mach wave are not correctly modelled because intrinsic attenuation is not included in the finite-difference calculation. The Mach cone angle from the snapshot agrees with the theoretical prediction. Finally, a finite-difference method was used to simulate Mach-wave propagation in a formation with two horizontal layers. In the case of two slow layers, the Mach-wave generated in the first layer is reflected back from and transmitted through the boundary and another Mach wave is generated at the second layer when the Stoneley wave travels into the second layer. In the case of a formation having one slow and one fast layer, the Mach wave generated in the slow layer is reflected back at the boundary and leaked into the fast layer. There is no Mach wave in the fast layer. 相似文献
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分析了相邻井下、地表地震计记录的背景噪声及近震、远震波形特征,以及相关的振幅谱及近震、远震接收函数波形特征。结果表明,井下地震计记录的背景噪声比地表地震计小1个数量级,其近震、远震波形记录较清晰、简洁;井下、地表地震计记录的远震振幅谱和径向接收函数具有较好的一致性,但背景噪声、近震振幅谱、近震接收函数、远震切向接收函数波形存在一定差异;由地表地震计得到的近震震级比井下地震计的大0.12,地表地震计到井下地震计之间的P波速度约为2 km/s。 相似文献
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用于低渗砂岩油气开发的压裂需要地层的纵横波时差参数;压裂形成的人工裂缝或砂泥岩中的自然裂缝是油气流入井中的主要通道.声波测井是测量地层的纵横波时差、探测连通裂缝的有效方法.本文给出了新设计的偶极子组合声波测井仪器在低渗砂泥岩地层所测量的波形.新仪器利用声波在井内传播的固有频率设计探头,利用探头阻抗随频率的变化曲线设计匹配电路,有效地提高了声发射功率,在井下采用16位A/D转换器提高了原始波形的采样精度.测量的波形比通常的声波测井波形所含的地层信息丰富.单极子长源距声波测井波形中除了通常的纵、横波和Stoneley波外,还发现了起始于纵波首波的反射波以及随深度改变其到达时间的后续波.通过与其它测井曲线综合对比发现:其反射波与井眼扩径有关,使测量的声波时差加大;后续波在显示地层特征的同时,与横波混叠在一起,使横波时差的提取变得困难.另外,在偶极子所测量的低频波形中也发现了明显的反映地层连通裂缝的反射波,该反射波可以用于指示低渗砂岩地层中的连通裂缝. 相似文献
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震电测井的现场试验中测得电磁首波幅值大于伴随电场幅值,这种情况在前人的理论模拟和模型井测量中从未出现.本文研究矿化度界面对震电测井波场的影响,基于Pride方程和边界连续条件模拟了震电测井波场,其中井外孔隙地层可以视为均匀的或者是径向分层的.计算结果表明:对于均匀孔隙地层,当井内流体矿化度大于井外地层孔隙流体矿化度时,电磁首波幅值可以比伴随斯通利波的电场幅值还大;井内流体矿化度与井外地层孔隙流体矿化度的比值越大,电磁首波相对伴随斯通利波的电场的幅值越大.对于径向分层地层,当井内流体矿化度大于内层地层的孔隙流体矿化度时,电磁首波幅值可以比伴随斯通利波的电场幅值还大;当外层地层矿化度小于内层地层矿化度时,电磁首波幅值可以比伴随斯通利波的电场幅值还大;增加内层地层厚度,电场全波幅值减小,电磁首波相对伴随电场的幅值减小.本文的模拟结果表明,震电测井中确实会出现电磁首波幅值比伴随电场幅值还大的情况,这对于解释震电测井的测量结果具有指导意义. 相似文献
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随钻情况下准确测量地层的纵波速度是当前声波测井领域亟待解决的技术难点之一,本文则针对地层纵波速度的随钻测量问题,在实验室内进行了缩小模型的随钻声波测井实验研究.首先,针对无限大流体模型,记录不同声源频率下单极源钻铤波的时域波形,研究钻铤内外两区域钻铤波的传播规律,定量分析这两部分钻铤波的频率响应特性.结果表明,随着声源激励频率的逐渐提高,钻铤波幅度呈现出先增大后减小的趋势,且中心频率两侧钻铤波幅度的变化规律不同.之后,针对小尺寸砂岩井孔模型,进行单极源随钻声波测井实验测量,进而比较两种模型下钻铤波的幅值差异性.最后,基于随钻声波测井原理和钻铤波的能量分布规律,提出一种地层纵波速度的提取方法,并进一步利用实测数据验证方法的可行性.结果表明:即使在钻铤不刻槽的情况下,通过能量剔除的方式亦可极大削弱测井全波中钻铤波的幅度,从而实现对地层纵波速度的准确测量. 相似文献
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In this paper, a method is proposed to invert permeability from seismoelectric logs in fluid‐saturated porous formations. From the analysis of both the amplitude and the phase of simulated seismoelectric logs, we find that the Stoneley wave amplitude of the ratio of the converted electric field to the pressure (REP) is sensitive to porosity rather than permeability while the tangent of the REP's phase is sensitive to permeability. The REP's phase reflects the phase discrepancy between the electric field and the pressure at the same location in the borehole. We theoretically derive the frequency‐dependent expression of the REP of the low‐frequency Stoneley wave and find that the tangent of the REP's argument is approximately in inverse proportion to permeability. We obtain an inversion formula and present the permeability inversion method by using the tangent of the REP's phase. To test this method, the permeabilities of different sandstones are inverted from the synthetic full‐waveform data of seismoelectric logs. A modified inversion process is proposed based on the analysis of inversion errors, by which the relative errors are controlled below 25% and they are smaller than those of the permeability inversion from the Stoneley wave of acoustic logs. 相似文献
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The phenomenon of acoustic waves inducing electric fields in porous media is called the seismoelectric effect. Earlier investigators proposed the usage of seismoelectric effect for well logging. Soil texture has a strong influence on the coupled wave fields during shallow surface explorations. In this article, we study the borehole pure shear‐horizontal wave and the coupling transverse‐electric field (acoustic–electrical coupling wave fields) in the partially saturated soil. Combined with related theories, we expand the formation parameters to partially saturated forms and discuss the influence of soil texture conditions on the seismoelectric wave fields. The results show that the elastic and electrical properties of porous media are sensitive to water saturation. The compositions of the acoustic and electric fields for different soil textures do not change, but the waveforms differ. We also use the secant integral method to simulate the interface‐converted electromagnetic waves. The results show that interface response strength is greatly influenced by soil texture. In addition, considering the sensitivity of the inducing electric field to fluid salinity, we also simulate the time‐domain waveforms of electric field for different pore fluid salinity levels. The results show that as the salinity increases, the electric field amplitude decreases monotonically. The above conclusions have certain significance for the application of borehole shear wave and its coupled electric fields for resource exploration, saturation assessment and groundwater pollution monitoring. 相似文献
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针对声电效应测井问题，提出了一种全波列数值模拟方法.该方法忽略声电效应测井 时转换电场对声场的影响,并将电场视为似稳场.采用点声源模型，依据Biot理论得出了井外 孔隙介质声场的表达式，运用这些表达式和似稳电场近似方法，导出了声电效应测井时转换 电场的计算公式.在计算出的转换电场波形中，有伴随斯通利波的电场、伴随纵波和横波的 电场、和临界折射电磁波场.在25kHz以下的频率范围内，依据这种方法计算出来的声电转换 波波形与依据完整Pride理论计算的波形一致. 相似文献
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The compression of soil grain and pore fluid as well as viscid coupling of pore fluid and soil skeleton is considered, the scattering problem of incident plane P1 wave （fast compressional wave） by an infinite cylindrical shell deeply embedded in isotropic saturated soils is studied by adopting the amended Biot model, amplitude equations about potential functions of scattering and refracting fields are obtained, and the effect of dimensionless frequencies and shell thickness on the back-scattering spectra and dynamic stress concentration factors of two types of cylindrical shells with high and low rigidity are numerically computed and analyzed. 相似文献