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1.
利用随机过程的谱展开理论以及Hudson等人的裂纹介质模型构造一种裂纹数密度是空间平稳随机过程的随机介质模型。这个模型可以将裂纹的微观参数(裂纹数密度)与裂纹介质的宏观性质(弹性常数)联系起来,能灵活、有效地描述实际非均匀裂纹介质。模型算例表明,弹性常数的空问分布特征与裂纹数密度的有差别,而且对不同的弹性常数影响不同。通过改编自相关长度的大小,可以模拟裂缝在两个坐标轴方向上具有不同分布尺度的情况。最后,利用高阶的交错网格有限差分方法,我们模拟了地震波在具有随机分布裂缝岩石中的传播特征。 相似文献
2.
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
3.
非常规油气藏（如致密性地层及蕴藏油气的页岩地层）的重要特征是低孔、低渗,但裂隙或裂缝比较发育.为满足非常规勘探的需求,本文将孔、裂隙介质弹性波传播理论应用于多极子声波测井的井孔声场模拟,重点研究了致密介质中裂隙发育时多极子声波的传播机理以及衰减特征.井孔声场的数值计算结果表明裂隙的存在明显改变了弹性波和井孔模式波的频散、衰减和激发强度,尤其是井壁临界折射纵波的激发谱的峰值随着频率的增加逐渐降低,这与应用经典的Biot理论下的计算结果相反,且裂隙的存在也使得饱含水和饱含气时临界折射纵波激发强度的差异变大.井孔模式波的衰减与地层横波衰减和井壁流体交换有关,井壁开孔边界下致密地层裂隙发育还使得井孔斯通利波和艾里相附近的弯曲波对孔隙流体的敏感性增强,在井壁闭孔边界条件下引起井孔模式波衰减的主要因素是裂隙引起的地层横波衰减造成的,且在截止频率附近弯曲波的衰减与地层的横波衰减一致.数值计算结果为解释非常规油气地层的声学响应特征提供了参考. 相似文献
4.
This paper presents the attenuation relations of peak ground acceleration and spectral accelerations for rock and soil sites in the central and eastern United States (CEUS). For the bedrock site condition, 56 pairs of moment magnitude M and epicentral distance R are used to simulate ground motion, and for each pair of M and R, 550 samples of ground motion parameters are generated using a seismological model together with random vibration theory and distribution of extreme values. From the regression analyses of these data, the attenuation relations of ground motion parameters for the bedrock site are established. With the aid of appropriate site coefficients, these attenuation relations are modified for the site categories specified in the 1994 NEHRP Provisions. These attenuation relations are appropriate for the assessment of seismic hazards at far-field rock and soil sites in the CEUS. 相似文献
5.
Omri Shitrit Yossef H. Hatzor Shimon Feinstein Vyacheslav Palchik Harold J. Vinegar 《Geophysical Prospecting》2019,67(3):624-650
The elastic moduli and anisotropy of organic-rich rocks are of great importance to geoengineering and geoprospecting of oil and gas reservoirs. In this paper, we probe into the static and dynamic moduli of the Ghareb–Mishash chalk through laboratory measurements and new analytical approaches. We define a new anisotropy parameter, ‘hydrostatic strain ratio’ (Ω), which describes the differential contraction of anisotropic rocks consequent to hydrostatic compression. Ω depends on the C11, C12, C13 and C33 stiffness constants of a transversely isotropic material, and therefore enables a unique insight into the anisotropic behaviour of TI rocks. Ω proves more sensitive to anisotropy within the weak anisotropy range, when compared with Thomsen's ε and γ parameters. We use Ω to derive static moduli from triaxial compression tests performed on a single specimen. This is done by novel employment of a hydrostatic-deviatoric combination for transversely isotropic elastic stiffnesses. Dynamic moduli are obtained from acoustic velocities measurements. We find that the bedding-normal velocities are described well by defining kerogen as the load-supporting matrix in a Hashin–Shtrikman model (‘Hashin–Shtrikman (HS) kerogen’). The dynamic moduli of the Ghareb–Mishash chalk in dry conditions are significantly higher than the static moduli. The dynamic/static moduli ratio decreases from ∼4 to ∼2 with increasing kerogen content. Both the static and dynamic moduli decrease significantly with increasing porosity and kerogen content. The effect of porosity on them is two times stronger than the effect of kerogen. 相似文献
6.
The earth media friction attenuates the energy of seismic wave. Obviously, that earth medium is treated as viscoelasticity is more appropriate than as elasticity. Seismic wave in visco-elastic media contains abundant lithology information of the medium. The investiga-tions of the solutions of visco-elastic wave equations, velocities of seismic wave propagating and the at-tenuation of seismic wave in the visco-elastic media are very important for geophysical prospecting tech-nology. Under a sma… 相似文献
7.
—The Nikko region, in northern Kanto, central Japan, which is a high seismicity region, is located near the volcanic front. Many seismic observations have been carried out around the Nikko region because the seismograms of the shallow earthquakes occurring in this region show an S-wave reflected phase (SxS) and an S-to-P mode-converted and reflected phase (SxP) from a mid-crustal seismic velocity discontinuity. The depth of the mid-crustal reflector was estimated to be about 9–16 km. From the amplitude analyses of SxS and SxP phases, the material of the mid-crustal layer just beneath the reflector was expected to be a low rigidity layer, which was interpreted as partially molten rocks. No evidence has been shown for the internal properties of the material of the reflector. The Vp/Vs ratio is a good measure to distinguish between the two candidates for seismic reflectors; i.e., partially molten rocks and rocks containing water. We investigate the Vp/Vs ratio of the reflector using the spectrum analyses of the data observed by a seismic array. From spectrum analysis of the data, we indicate that the Vp/Vs ratio of 2.5 is better than that of 1.8 to explain the observed data, which shows that the material beneath the reflector consists of partially molten rocks. 相似文献
8.
深入了解不同压力、频率、流体含量和流体分布对岩石中弹性波传播特性的影响,对指导油气勘探开发具有重要意义.不同尺度下的波致流效应,是声波传播过程中产生速度频散和衰减的重要原因.本文以不同压力下水饱和区域改进的骨架模量为纽带,建立了联合介观尺度斑块饱和效应与微观尺度喷射流效应的部分饱和岩石声学理论模型.开展针对性声学实验,根据不同压力下部分饱和砂岩纵波速度测量数据,确定理论模型中的相关参数,从而实现对不同压力下部分饱和岩石纵波衰减的定量表征.在此基础上,通过理论与实验测量的纵波衰减的对比,分析不同压力、含水饱和度以及频率对岩石纵波衰减的影响.研究结果表明,在较低压力,较高含水饱和度以及较高频段,喷射流效应较强,因此新建模型计算的衰减明显大于斑块饱和模型的衰减.由于新建模型体现了斑块饱和效应与喷射流效应的综合影响,相比于斑块饱和模型,新建模型计算的部分饱和岩石的纵波衰减更接近于实测衰减,但受到岩石自身因素影响,新建模型计算的衰减仍略小于实测衰减. 相似文献
9.
10.
Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle.This paper examines the behavior of seismic waves attenuation caused by the internal structure of rock mass,and in particular,the internal geometry of the distribution of fluid-filled openings Systematic research on the effect of crack parameters,such as crack density,crack aspect ratio(the ratio of crack thickness to crack diameter),pore fluid properties(particularly pore fluid velocity),VP/VS ratio of the matrix material and seismic wave frequency on attenuation anisotropy has been conducted based on Hudson’s crack theory.The result shows that the crack density,aspect ratio,material filler,seismic wave frequency,and P-wave and shear wave velocity in the background of rock mass,and especially frequency has great effect on attenuation curves.Numerical research can help us know the effect of crack parameters and is a good supplement for laboratory modeling.However,attenuation is less well understood because of the great sensitivity of attenuation to details of the internal geometry.Some small changes in the characteristics of pore fluid viscosity,pore fluids containing gas and liquid phases and pore fluids containing clay can each alter attenuation coefficients by orders of magnitude.Some parameters controlling attenuation are therefore necessary to make reasonable estimations,and anisotropic attenuation is worth studying further. 相似文献
11.
R. Agersborg M. Jakobsen B. O. Ruud T. A. Johansen 《Studia Geophysica et Geodaetica》2007,51(1):89-118
An effective medium model for the stress-dependent seismic properties of fractured reservoirs is developed here on the basis
of a combination of a general theory of viscoelastic waves in rock-like composites with recently published formulae for deformation
of communicating and interacting cavities (interconnected pores/cracks and fractures at finite concentration) under drained
loading. The inclusion-based model operates with spheroidal cavities at two different length scales; namely, the microscopic
scale of the pores and (grain-boundary) cracks, and the mesoscopic scale of the fractures (controlling the flow of fluid).
The different cavity types can in principle have any orientation and aspect ratio, but the microscopic pores/cracks and mesoscopic
fractures were here assumed to be randomly and vertically oriented, respectively. By using three different aspect ratios for
the relatively round pores (representing the stiff part of the pore space) and a distribution of aspect ratios for the relatively
flat cracks (representing the compliant part of the pore space), we obtained a good fit between theoretical predictions and
ultrasonic laboratory measurements on an unfractured rock sample under dry conditions. By using a single aspect ratio for
the mesoscopic fractures, we arrived at a higher-order microstructural model of fractured porous media which represents a
generalization of the first-order model developed by Chapman et al. (2002,2003). The effect of cavity size was here modelled
under the assumption that the characteristic time for wave-induced (squirt) flow at the scale of a particular cavity (pore/crack
vs. fracture) is proportional with the relevant scale-size. In the modelling, we investigate the effect of a decreasing pore
pressure with constant confining pressure (fixed depth), and hence, increasing effective pressure. The analysis shows that
the attenuation-peak due to the mesoscopic fractures in the reservoir will move downward in frequency as the effective pressure
increases. In the range of seismic frequencies, our modelling indicates that the P-wave velocities may change by more than
20% perpendicular to the fractures and close to 10% parallel to the fractures. In comparison, the vertical S-wave velocities
change by only about 5% for both polarization directions (perpendicular and parallel to the fractures) when the effective
pressure increases from 0 to 15 MPa. This change is mainly due to the overall change in porosity with pressure. The weak pressure
dependence is a consequence of the fact that the S waves will only sense if the fractures are open or not, and since all the
fractures have the same aspect ratio, they will close at the same effective pressure (which is outside the analysed interval).
Approximate reflection coefficients were computed for a model consisting of the fractured reservoir embedded as a layer in
an isotropic shale and analysed with respect to variations in Amplitude Versus Offset and aZimuth (AVOZ) properties at seismic
frequencies for increasing effective pressure. For the P-P reflections at the top of the reservoir, it is found that there
is a significant dependence on effective pressure, but that the variations with azimuth and offset are small. The lack of
azimuthal dependence may be explained from the approximate reflection coefficient formula as a result of cancellation of terms
related to the S-wave velocity and the Thomson’s anisotropy parameter δ. For the P-S reflection, the azimuthal dependence
is larger, but the pressure dependence is weaker (due to a single aspect ratio for the fractures).
Finally, using the effective stiffness tensor for the fractured reservoir model with a visco-elastic finite-difference code,
synthetic seismograms and hodograms were computed. From the seismograms, attenuation changes in the P wave reflected at the
bottom of the reservoir can be observed as the effective pressure increases. S waves are not much affected by the fractures
with respect to attenuation, but azimuthal dependence is stronger than for P waves, and S-wave splitting in the bottom reservoir
P-S reflection is clearly seen both in the seismograms and hodograms. From the hodograms, some variation in the P-S reflection
with effective pressure can also be observed. 相似文献
12.
— We develop a new scheme to compute 2-D SH seismograms for media with many flat cracks, based on the boundary integral method. A dry or traction-free boundary condition is applied to crack surfaces although other kinds of cracks such as wet or fluid-saturated cracks can be treated simply by assigning different boundary conditions. While body forces are distributed for cavities or inclusions to express scattered wave, dislocations (or displacement discontinuities between the top and the bottom surfaces of each crack) are used as fictitious sources along crack surfaces. With these dislocations as unknown coefficients, the scattered wave is expressed by the normal derivative of Green's function along the crack surface, which is called “double-layer potentials” in the boundary integral method, while we used “single-layer potentials” for cavities or inclusions. These unknowns are determined so that boundary conditions or crack surfaces are satisfied in the least-squared sense, for example, traction-free for dry cracks. Seismograms with plane-wave incidence are synthesized for homogeneous media with many cracks. First, we check the accuracy of our scheme for a medium with one long crack. All the predicted phases such as reflected wave, diffraction from a crack tip and shadow behind the crack are simulated quite accurately, under the same criterion as in the case for cavities or inclusions. Next, we compute seismograms for 50 randomly distributed cracks and compare them with those for circular cavities. When cracks are randomly oriented, waveforms and the strength of scattering attenuation are similar to the cavity case in a frequency range higher than k d $\simeq$ 2 where the size of scatterers d (i.e., crack length or cavity diameter) is comparable with the wavelength considered (k is the wavenumber). On the other hand, the scattering attenuation for cracks becomes much smaller in a lower frequency range (k d<2) because only the volume but not detail geometry of scatterers becomes important with wavelength much longer than each scatterer. When all the cracks are oriented in a fixed direction, the scattering attenuation depends strongly on the incident angle to the crack surface as frequency increases (k d>2): scattering becomes weak for cracks oriented parallel to the direction of the incident wave, while it gets close to the cavity case for cracks aligned perpendicular to the incident wave. 相似文献
13.
地下多孔介质中的孔隙类型复杂多样,既有硬孔又有扁平的软孔.针对复杂孔隙介质,假设多孔介质中同时含有球型硬孔和两种不同产状的裂隙(硬币型、尖灭型裂隙),当孔隙介质承载载荷时,考虑两种不同类型的裂隙对于孔隙流体压力的影响,建立起Biot理论框架下饱和流体情况含混合裂隙、孔隙介质的弹性波动方程,并进一步求取了饱和流体情况下仅由裂隙引起流体流动时的含混合裂隙、孔隙介质的体积模量和剪切模量,随后,在此基础上讨论了含混合裂隙、孔隙介质在封闭条件下地震波衰减和频散的高低频极限表达式.最后计算了给定模型的地震波衰减和频散,发现地震波衰减曲线呈现"多峰"现象,速度曲线为"多频段"频散.针对该模型分析讨论了渗透率参数、裂隙纵横比参数以及流体黏滞性参数对于地震波衰减和频散的影响,表明三个参数均为频率控制参数. 相似文献
14.
由于介观尺度的孔隙流体流动,弹性波传播过孔隙岩层时在地震频段表现出较强的频散和衰减。Johnson理论给出了在任意孔隙形状的条件下,部分气水饱和孔隙介质的理论相速度和品质因子的解析解。本文在Johnson模型的基础上,通过对Q值曲线的低频和高频近似,推导了Q值曲线的近似公式,以及基于孔隙介质基本地球物理参数和孔隙斑块几何形态参数T和比表面积S/V的最大衰减Qmin近似公式。通过与理论值的对比,对Qmin近似公式存在的线性误差进行改正,进一步提高了精度。复杂的斑块形态对最大衰减Qmin和过渡频率ftr的都产生一定影响,且对ftr影响更大。因为数值模拟直接求解介观尺度的Biot孔隙介质方程需要极大的计算量,我们使用Zener模型建立了等效粘弹模型,有效地模拟了地震频带内的衰减和频散现象。 相似文献
15.
地震波本征衰减反映了地层及其所含流体的一些特性,对油气勘探开发有重要意义.已有的理论研究与实验发现,地震频带内的衰减主要与中观尺度(波长与颗粒尺度之间)的斑状部分饱和、完全饱和岩石弹性非均匀性情况下波诱导的局部流体流有关.这种衰减与岩石骨架、孔隙度及充填流体的性质密切相关.本文着重讨论均匀流体分布、斑状或非均匀流体分布两种情况下部分饱和岩石的纵波模量差异.以经典岩石物理理论和衰减机制认识为基础,通过分析低频松弛状态、高频非松弛状态岩石的弹性模量,讨论储层参数(如孔隙度、泥质含量以及含水饱和度等)与纵波衰减之间的确定性关系.上述方法与模型在陆相砂泥岩地层与海相碳酸盐岩地层中的适用性通过常规测井资料得到了初步验证. 相似文献
16.
Yu. A. Alkhimenkov 《Izvestiya Physics of the Solid Earth》2017,53(3):477-487
Various methods of the effective medium theory (EMT)—the T-matrix approach (optical potential approximation and coherent potential approximation), Mori–Tanaka method, generalized singular approximation, etc.—for modeling the effective elastic properties of hydrocarbon reservoir rocks are considered. The relationship of the different approaches (perturbation theory, self-consistent methods, and variational principles) is demonstrated. The classification of the methods by the degree of complexity of solving the inverse problem is suggested. An example of the theoretical modeling of an oil-, gas-, and water-saturated rock with the oriented axis of the fractures is presented. Conclusions about the applicability of different methods for rock modeling are made. In this study we review and compare different methods of the EMT and present the guidelines for determining the effective properties of the medium in rock physics modeling. 相似文献
17.
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
18.
Abstract Groundwater development potential in northern Ghana (108 671 km2) has been assessed by combining spatial layers for five critical factors—recharge rate, regolith thickness, transmissivity, borehole success rate and static water level—through a multi-criteria analysis approach to rank development potential from the viewpoint of groundwater availability and accessibility at a resolution of 1 km2. The results indicate a high potential for development in the study area, as about 70% of the area was found to have high to moderate groundwater availability, while 83% has high to medium groundwater accessibility. Comparing the two main hydrogeological environments, the Precambrian Basement rocks (PCB) area was found to generally have a higher groundwater development potential than the Voltaian Sedimentary rocks (VSB). More detailed investigation revealed that the VSB can produce a small proportion of exceptionally high-yielding boreholes that can support large-scale irrigation. A test of the reliability of results showed that generally, the majority of high- and low-yielding boreholes fall in areas predicted by the model as having high and low groundwater availability, respectively. Editor D. Koutsoyiannis; Associate editor D. Hughes Citation Forkuor, G., Pavelic, P., Asare, E., and Obuobie, E., 2013. Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS. Hydrological Sciences Journal, 58 (2), 437–451. 相似文献
19.
Ajoy Roy Choudhury 《Pure and Applied Geophysics》1970,80(1):137-146
Summary The propagation of disturbances in cylindrical surfaces of visco-elastic material of general linear type (i) cylinder surrounded by a vacuum (ii) and on an infinite body of same material having a cylindrical cavity, when the surface is subjected to an initially static magnetic field, making use of the electro-magnetic equations of Maxwell, equations of elasticity and the stress-strain relations of the material. 相似文献
20.
M. Nafi Toksöz Anton M. Dainty Edmund Reiter Ru-Shan Wu 《Pure and Applied Geophysics》1988,128(1-2):81-100
The mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data, coda wavesRg attenuation, strong motion attenuation measurements in the northeast United States and Canada, and theoretical models. The frequency range 1–10 Hz has been studied. The relative contributions to attenuation of anelasticity of crustal rocks (constantQ), fluid flow and scattering are evaluated. Scattering is found to be strong with an albedoB
0=0.8–0.9 and a scattering extinction length of 17–32 km. The albedo is defined as the ratio of the total extinction length to the scattering extinction length. TheRg results indicate thatQ increases with depth in the upper kilometer or two of the crust, at least in New England. CodaQ appears to be equivalent to intrinsic (anelastic)Q and indicates that thisQ increases with frequency asQ=Q
o
f
n
, wheren is in the range of 0.2–0.9. The intrinsic attenuation in the crust can be explained by a high constantQ (500Q
o2000) and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks. A fluid-flow attenuation model gives a frequency dependence (QQ
o
f
0.5) similar to those determined from the analysis of coda waves of regional seismograms.Q is low near the surface and high in the body of the crust. 相似文献