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1.
由弹性波纵横波速比计算得到的泊松比,在利用地震波反演地下结构和物质组成时,可以提供比单纯地利用纵波或者横波波速更强的约束. 为了研究不同岩石中泊松比及其各向异性随围压的变化,选取19块典型的岩石样品,在不同围压下沿相互正交的3个方向同时测量纵、横波速度,并通过计算得到了泊松比及其各向异性. 结果表明,在大部分样品中泊松比各向异性与纵波速度各向异性有一定的相关性,但在有的样品中泊松比各向异性与纵波速度各向异性没有明显的关系,甚至表现出完全相反的变化规律. 由于泊松比也表现出很强的各向异性,在排除微裂隙的影响后有的仍可以达到30髎以上,在利用实际地震波传播数据通过泊松比反演地下物质结构时必须考虑其各向异性的影响. 相似文献
2.
库车坳陷属于高陡构造地区,油气资源丰富,勘探潜力巨大.但是该地区地下构造复杂,断裂发育,地层倾角陡,地震波场复杂,地震成像品质较差是制约库车复杂构造研究的主要因素.零井源距VSP资料波场上转换横波很发育,波场记录上转换横波和纵波同时存在造成该地区地面地震波场相当复杂,影响地面地震资料的成像品质.因此为了避免地面地震资料处理过程中各种波场的相互影响,利用VSP波场信息能防止地面地震资料处理过程中可能出现的"陷阱".本文充分发挥VSP波场信息丰富的特点,通过库车坳陷高陡构造地区零井源距VSP波场正演模拟和实际资料波场分析,准确识别纵波和转换横波波场,并利用有效的波场分离手段分离出VSP纵波波场和VSP转换横波波场.通过VSP纵横波波场与实际地面地震资料对比,能很好地识别出了地面地震资料上的纵波和转换横波波场,为库车坳陷高陡构造地区地面地震资料处理提供参考依据.研究表明:库车坳陷高陡构造地区转换横波在地震纵波成像中影响较大,建议库车坳陷高陡构造地区地面地震处理要加强转换横波的识别与应用,进一步加强井地联合处理攻关研究,获得更可靠、更高品质的纵波资料,同时也能得到更为丰富的转换横波资料. 相似文献
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转换波偏移可以利用纵横波波场信息,得到高分辨率的成像结果,从而为油藏描述提供高质量的地震资料.目前的研究主要是利用纵波波场信息进行偏移成像,然而,传统的纵波方法在复杂探区成像时具有一定的局限性.为此,本文在各向异性介质声波射线追踪算法的基础上,推导出各向异性介质转换波射线追踪方程,发展了一种转换波射线追踪算法;并将研究的追踪算法应用到偏移成像中,提出了一种各向异性VTI介质角度域转换波高斯束偏移成像方法.通过各向异性VTI介质断块模型和复杂构造模型试算,说明了本文方法的正确性和有效性.模型试算的结果表明,在考虑地下各向异性时,本文研究的方法具有更好的成像效果,提取的角道集结果可以为偏移速度分析提供依据. 相似文献
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实验室可以产生两种振动模式的横波,一种是剪切振动,另一种是扭转振动.本文利用扭转换能器观测了扭转横波在各向异性样品中的传播特性.实验表明,无偏振方向的扭转波在各向异性介质中会以两种不同速度传播,并出现波的分裂现象,其快慢波的速度值与剪切横波的快慢横波速度一致.用扭转波换能器接收时,快慢扭转波的波形振幅不受各向异性方位影响,表现为无方向性.通过两块不同来源的均匀各向异性样品,用实验观测方式初步揭示了各向异性介质中扭转波的一些传播特征. 相似文献
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由于各向异性广泛存在于地下岩石中,随着勘探精度的不断提高,对地下介质的各向同性假设越来越不能够满足于现状,因此对各向异性介质的数值模拟显得更为重要。本文推导了各向异性介质的弹性波动方程,总结了震源类型,通过PML方法处理了人工边界问题,通过快照分析验证了数值频散、稳定性条件。研究结果表明:① PML完全匹配层,可较好地解决人工边界问题;②减小空间采样间隔压制数值频散比减小时间采样间隔效果要好得多,盲目减小时间采样间隔会大大降低数值模拟的运算效率;③各向异性介质中弹性波场中除含有准纵波外,还含有速度较慢的准横波;④准纵波波前能量要比由各向异性引起的准横波能量强,准纵波和准横波的波前随着各向异性介质参数的变化而变化。 相似文献
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利用新方法制作出含可控裂缝的双孔隙人工砂岩物理模型,具有与天然岩石更为接近的矿物成分、孔隙结构和胶结方式,其中裂缝密度、裂缝尺寸和裂缝张开度等裂缝参数可以控制以得到实验所需要的裂缝参数,岩样具有真实的孔隙和裂缝空间并可以在不同饱和流体状态下研究流体性质对于裂缝介质性质的影响.本次实验制作出一组具有不同裂缝密度的含裂缝人工岩样,对岩样利用SEM扫描电镜分析可以看到真实的孔隙结构和符合我们要求的裂缝参数,岩样被加工成八面棱柱以测量不同方向上弹性波传播的速度,用0.5 MHz的换能器使用透射法测量在饱和空气和饱和水条件下各个样品不同方向上的纵横波速度,并得出纵横波速度、横波分裂系数和纵横波各向异性强度受裂缝密度和饱和流体的影响.研究发现流体对于纵波速度和纵波各向异性强度的影响较强,而横波速度、横波分裂系数和横波各向异性强度受饱和流体的影响不大,但是对裂缝密度的变化更敏感. 相似文献
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当地下介质存在各向异性时,在观测坐标系下的弹性参数与自然坐标系下的弹性参数不一定相同．首先,根据势能密度和耗散能密度与坐标轴无关的原理,推导出了双相各向异性介质中观测坐标系下弹性参数与自然坐标系下弹性参数之间的关系;然后,从任意双相各向异性中弹性波波动方程出发,得出了该方程的伪谱法数值解法;最后,通过数值模拟,观测到了存在于双相各向异性介质中的４类波,即快纵波、慢纵波、快横波和慢横波．在双相各向异性介质中,ＳＶ波传播的波前面上仍然存在波面尖角,这些尖角在界面上要发生反射和透射．另外,数值模拟结果中可见转换慢纵波和慢纵波的转换波． 相似文献
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在沉积学中,可假设在相同时期的沉积层具有相近的物理性质和演化过程.因此,沿层传播的地震波和垂直于地层传播的地震波具有各向异性的特点.在纵波资料的处理中,考虑各向异性对逆时偏移的影响,通常假设介质的横波速度为零,这样可以得到纵波在TTI介质中的传播方程,但是该方程在实际计算中仍存在数值稳定性问题.本文加入横波分量可有效解决数值稳定性问题,并选取适当的横波速度减小对纵波成像的影响,实现地震波在TTI介质中的逆时偏移.实际测算表明,P-SV波的方程中包含横波分量,若假设SV的速度为零,则会导致方程的差分格式不稳定;若加入SV波,选择合适的SV波速度可以使SV波的全区各向异性和反射系数达到极小,并可有效的抑制SV波对纵波勘探的影响.本文的方法是一种稳定的TTI介质中的逆时偏移方法. 相似文献
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选择４种地壳岩石样品,经干燥或水饱和处理后在不同围压条件下测量了在其中传播的纵、横波的速度及其各向异性．在大气压条件下低孔隙度(＜１％岩样中,水饱和样品中的纵波速度明显地比干燥样品中的高,但横波速度的差别不大．因为在低孔隙度岩样中纵波速度对孔隙流体的反应比横波速度敏感,可以用泊松比的变化来反映随着围压的增加晶粒间流体对弹性波传播特性的影响．根据实验数据,按Ｏ’Ｃｏｎｎｅｌｌ模型分别计算了干燥和水饱和岩样中的裂纹密度,与通过实测体应变曲线得到的裂纹孔隙度十分吻合．利用横波的速度和偏振特性可以推断岩样中定向排列微裂纹的空间取向情况．研究表明,同时测量在岩样中传播的纵、横波的速度,通过Ｖｐ／Ｖｓ比值可以给出有关颗粒边界流体的证据,也可以估计岩样中的裂纹密度． 相似文献
10.
常规叠前反演大都是利用P-P纵波单分量资料基于各向同性理论的近似公式来反演,仅利用P-P纵波资料反演地层岩性等弹性参数,无论在理论基础还是反演精度上都存在不足,且反演结果具有多解性.而同时用P-P纵波和P-SV转换波资料联合反演,可以增加约束条件,提高反演结果的稳定性、可靠性.本文以各向异性理论为基础,利用实际3D3C资料,进行了P-P纵波、P-SV转换波联合叠前反演计算,P-P纵波、P-SV转换波叠前联合反演利用了纵波和转换波的叠前资料,尽可能保留了地层的AVO信息,输入数据增加了转换横波数据,同时利用了纵波和转换波两个独立变量信息,采用完全Knott-Zoeppritz方程求解,反演结果比P-P纵波单分量资料叠前反演更稳定、可靠、反演精度明显提高.研究区实际资料计算结果表明,反演结果可以更真实的反映储层段的物性和含气性,P-P纵波、P-SV转换波联合叠前反演比P-P纵波单分量资料叠前反演预测储层符合率提高了十个百分点,该反演方法是一种有效的反演方法. 相似文献
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S. CRAMPIN 《Geophysical Prospecting》1986,34(1):94-99
A number of authors in the exploration literature have written about anisotropy, but have restricted their discussions to wave propagation through rock having transverse isotropy with a vertical symmetry axis. This note shows that there are fundamental differences between transverse isotropy when the symmetry axis is vertical (normal to the free surface) and more general anisotropy with an azimuthal variation of properties. These differences are important now that effective azimuthal shear-wave anisotropy resulting from aligned cracks and pores is becoming recognized as a significant property of crustal rocks. 相似文献
12.
Hydraulic fracturing reservoir reconstruction technology is crucial in the development of shale gas exploitation techniques.Large quantities of high-pressure fluids injected into shale reservoirs significantly alter compressional(P)and shear(S)wave velocities,rock mechanical parameters,and anisotropic characteristics.In this study,differentiated hydraulic fracturing petrophysical experiments were carried out on Longmaxi Formation shale under pseudo-triaxial stress loading conditions.The effects of stress loading methods,and water-rock physical and chemical reactions on P-and S-wave velocities and rock mechanical parameters were compared.The experimental results showed that isotropic stress loading may increase the P-and Swave velocities and Young’s modulus of dry shale kldnsample.Furthermore,it may lead to a weakening of the corresponding anisotropy.In contrast,differential stress loading was able to improve the anisotropy of Young’s modulus and accelerate the decrease in the compressive strength of shale in the vertical bedding direction.The water-rock physical and chemical reactions prompted by hydraulic fracturing was found to"soften"shale samples and reduce Young’s modulus.The influence of this"soften"effect on the compressional and shear wave velocities of shale was negligible,whilst there was a significant decrease in the anisotropy characteristics of Thomsen parameters,Young’s modulus,and Poisson’s ratio.The negative linear relationship between the Poisson’s ratios of the shale samples was also observed to lose sensitivity to stress loading,as a result of the"soften"effect of fracturing fluid on shale.The results of this study provide a reliable reference point and data support for future research on the mechanical properties of Longmaxi shale rocks. 相似文献
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裂缝诱导的双相具有水平对称轴的横向各向同性(HTI)介质模型是由一组平行排列的垂直裂缝嵌入到统计各向同性的流体饱和多孔隙岩石中而组成的,它综合考虑了裂缝型储层岩石的各向异性和孔隙性.高精度的地震波场数值模拟技术是研究该介质中地震波传播规律的主要方法.本文结合错格伪谱法和时间分裂法,求解描述该介质中地震波传播的一阶速度-应力方程.模拟了单层和双层模型中的地震波场,并对其进行了特征分析.研究结果表明:错格伪谱法能有效消除标准网格伪谱法波场模拟结果中出现的数值伪影现象,与时间分裂法结合能够获得稳定的、高精度的模拟结果;裂缝诱导双相HTI介质中的地震波场兼具裂缝各向异性介质和双相介质中传播的地震波的波场特征. 相似文献
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实际的地球介质十分复杂,远非当今人们所采用的理想模型可以概括,因为其属性和结构的变异是非均匀、非线性和各向异性的.在研究地球内部壳幔介质与结构、构造与属性差异、金属矿产资源和油、气、煤能源的勘查中,无论是区域构造格局、岩相和结构特征(如裂缝、破碎带、不同尺度的洞穴以及一些不规则几何体)均十分复杂.近年来基于成山、成盆、成矿、成岩和成灾研究的不断深化,对地下介质各向异性的研究受到广泛的关注.地震波动传播理论和介质与结构的物理属性研究结果表明:地震各向异性在成因上主要是由岩石、矿物和晶体的晶格优势取向、应力场异常变异和构造裂缝与深部物质运移造成的.为此,本文对14次地震各向异性会议的主体内涵进行分析,在此基础上,指出了在各向异性研究的发展进程中、特别是在应用中尚存在着的一些问题.在深化认识地球内部物质物理属性的基础上,探讨了S波分裂和偏振效应与地震各向异性与介质结构分区、构造活动,油气田勘探与岩相特征,裂隙与构造精细刻划和地震活动区(带)深部介质与构造环境的深层过程和动力学响应的关系.最后提出了地震各向异性在地球物理学发展中的作用和今后的任务. 相似文献
15.
Distinguishing oil and water layers by interpreting acoustic logging data with changing well diameters 
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下载免费PDF全文 During surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers, research on the properties of well diameters and oil and water layers and their relation to acoustic logging rules is essential. Using Hudson's crack theory, we simulated oil and water layers with different well diameters or crack parameters (angle and number density). We found that when the well radius increases from 0.03 m to 0.05 m, the variation ratio of compressional wave amplitude for the oil layer is less than that for the water layer. The difference of Stoneley wave amplitude between the crack parameters (angle and number density) is greater in the case of the water layer than in the case of the oil layer. The response sensitivity of wave energy is greater for the water layer than that for the oil layer. When the well radius increases from 0.05 m to 0.14 m, the maximum excitation intensity for oil layer is greater than that for the water layer. We conclude that the propagation of an elastic wave is affected by medium composition and well diameter, and the influence has certain regularity. These results can guide further reservoir logging field exploration work. 相似文献
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We address the issue of linearity and scale dependence in forward modelling of seismic data from well logs, for large ray parameters, wide angles or large offsets. We present a forward model, within the context of seismic‐to‐well matching, that is linearized in the elastic properties of the earth. This model preserves linearity at large ray parameters and can handle fine‐layering effects such as induced anisotropy. Starting from a low‐contrast small‐ray‐parameter model, we extend it to a large‐ray‐parameter model by fully linearizing the elastic‐property contrasts. Overall linearity of the forward model is extended by partitioning the compressional‐wave and shear‐wave velocity fields into two fundamental scales: a kinematic scale that governs wavefield propagation effects and a dynamic scale that governs wavefield scattering effects. This analysis reveals that the standard practice in forward modelling of strongly filtering the ratio of compressional‐wave velocity to shear‐wave velocity is well founded in the underlying physics. The partitioning of the velocity fields also leads naturally to forward modelling that accounts fully for stretch effects, to resolution of the angle‐of‐incidence versus ray‐parameter dichotomy in seismic‐amplitude analysis, and to full accounting for induced anisotropy and dispersion effects due to fine‐layering of isotropic media. With the onset of routine long‐offset acquisition and the compelling need to optimize asset management in order to maximize reserve recovery, this forward model recognizes the physics of seismic wave propagation and enables a more complete exploitation of amplitude information in pre‐critical seismic data. 相似文献
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Kirchhoff–Helmholtz (KH) theory is extended to synthesize two-way elastic wave propagation in 3D laterally heterogeneous, anisotropic media. I have developed and tested numerically a specialized algorithm for the generation of three-component synthetic seismograms in multi-layered isotropic and transversely isotropic (TI) media with dipping interfaces and tilted axes of symmetry. This algorithm can be applied to vertical seismic profile (VSP) geometries and works well when the receiver is located near the reflector interface. It is superior to ray methods in predicting elliptical polarization effects observed on radial and transverse components. The algorithm is used to study converted-wave propagation for determining fracture-related shear-wave anisotropy in realistic reservoir models. Results show that all wavefront attributes are strongly affected by the anisotropy. However, it is necessary to resolve a trade-off between the effects of fractures and formation dip prior to converted-wave interpretation. These results provide some assurance that the present scheme is sufficiently versatile to handle shear wave behaviour due to various generalized rays propagating in complex geological models. 相似文献
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O.H. Al‐Harrasi A. Al‐Anboori A. Wüstefeld J.‐M. Kendall 《Geophysical Prospecting》2011,59(2):227-243
The study of seismic anisotropy in exploration seismology is gaining interest as it provides valuable information about reservoir properties and stress directions. In this study we estimate anisotropy in a petroleum field in Oman using observations of shear‐wave splitting from microseismic data. The data set was recorded by arrays of borehole geophones deployed in five wells. We analyse nearly 3400 microearthquakes, yielding around 8500 shear‐wave splitting measurements. Stringent quality control reduces the number of reliable measurements to 325. Shear‐wave splitting modelling in a range of rock models is then used to guide the interpretation. The difference between the fast and slow shear‐wave velocities along the raypath in the field ranges between 0–10% and it is controlled both by lithology and proximity to the NE‐SW trending graben fault system that cuts the field formations. The anisotropy is interpreted in terms of aligned fractures or cracks superimposed on an intrinsic vertical transversely isotropic (VTI) rock fabric. The highest magnitudes of anisotropy are within the highly fractured uppermost unit of the Natih carbonate reservoir. Anisotropy decreases with depth, with the lowest magnitudes found in the deep part of the Natih carbonate formation. Moderate amounts of anisotropy are found in the shale cap rock. Anisotropy also varies laterally with the highest anisotropy occurring either side of the south‐eastern graben fault. The predominant fracture strikes, inferred from the fast shear‐wave polarizations, are consistent with the trends of the main faults (NE‐SW and NW‐SE). The majority of observations indicate subvertical fracture dip (>70° ). Cumulatively, these observations show how studies of shear‐wave splitting using microseismic data can be used to characterize fractures, important information for the exploitation of many reservoirs. 相似文献