Acoustic wave dispersion and attenuation in marine sediment based on partially gas-saturated Biot-Stoil model

利用含气非饱和Biot-Stoll模型研究了声波在海底表层沉积物介质中的传播,讨论了骨架耗散、含气饱和度对快纵波、慢纵波和横波速度和衰减的影响,并与Biot模型的结果进行了对比.研究结果表明:孔隙流体黏滞耗散与骨架耗散共同影响声波传播速度和衰减,低频情况下骨架耗散引起的衰减占主要地位,高频情况下骨架耗散引起的衰减较小;少量气体(＜1％)的引入显著改变了快纵波速度,气体含量的变化对快纵波衰减影响很大,低频情况下气体对慢纵波速度的影响不大,而对横波速度的影响较大,气体含量的变化对慢纵波和横波衰减影响较小.利用超声波测量系统测量了一例杭州湾海底沉积物样品的纵波速度和衰减,当含气量趋近0％时,Biot-Stoll模型预测的纵波速度和实验测量结果较为一致.     

基于非饱和Biot-Stoll模型的海底沉积物介质声频散特性研究

利用含气非饱和Biot-Stoll模型研究了声波在海底表层沉积物介质中的传播,讨论了骨架耗散、含气饱和度对快纵波、慢纵波和横波速度和衰减的影响,并与Biot模型的结果进行了对比.研究结果表明:孔隙流体黏滞耗散与骨架耗散共同影响声波传播速度和衰减,低频情况下骨架耗散引起的衰减占主要地位,高频情况下骨架耗散引起的衰减较小;少量气体(<1%)的引入显著改变了快纵波速度,气体含量的变化对快纵波衰减影响很大,低频情况下气体对慢纵波速度的影响不大,而对横波速度的影响较大,气体含量的变化对慢纵波和横波衰减影响较小.利用超声波测量系统测量了一例杭州湾海底沉积物样品的纵波速度和衰减,当含气量趋近0%时,Biot-Stoll模型预测的纵波速度和实验测量结果较为一致.     

砂岩和大理岩纵波速度及Q值实验研究

利用新近完成的弹性波参数测量系统,我们在静水压力(常压—32MPa)范围内,对不同饱和度砂岩和大理岩的纵波速度和Q 值进行了测试.结果表明,随着静水压力和饱和度的增加,砂岩和大理岩的纵波速度均增加;砂岩的Q 值随静水压力增加,但随饱和度减小.有关静水压力、孔隙流体对岩石纵波和Q 值的影响机理也作了简要论述.     

疏松砂岩气藏地震AVO属性敏感性分析与评价

利用完全Zoeppritz方程分析了疏松砂岩气藏反射系数对密度比、纵波速度比、横波速度比、泊松比和含气饱和度的敏感性.通过求取反射系数对各弹性参数的偏导得到反射系数对弹性参数的敏感性,通过求取反射系数对含气饱和度的完全导数得到对含气饱和度的敏感性.对于疏松砂岩气藏界面,P-P波AVO(振幅随偏移距变化)当入射角大于40°对纵波速度比、横波速度比在低含气饱和度时敏感,对泊松比的敏感性在气层饱和度较高和较低时差异明显,对含气饱和度的敏感性在低饱和度时敏感,且随入射角增加而增大;P-SV波AVO对泊松比的敏感性在含气饱和度较高和较低时差异明显.研究表明,利用反射系数对弹性参数和含气饱和度的敏感性分析可以帮助识别低饱和气藏.     

含气饱和度对致密砂岩纵波速度影响的实验研究及应用

本文为探索声波速度和含气饱和度之间的关系,对取自鄂尔多斯盆地致密砂岩层的岩心在不同的含气饱和度下进行了纵波速度的测量,结果表明:(1)岩心含水饱和时的的纵波速度要比含气饱和时的大;(2)含气饱和度大于70%时,纵波速度对含气饱和度的变化反映不敏感,或随着含气饱和度的增大略有增加,含气饱和度小于70%时,纵波速度随着含气饱和度增大近似成线性降低;(3)该实验研究为声波测井数据指示气层奠定了一定的理论基础,为致密砂岩层气层的识别提供了依据;(4)本文建立了纵波速度随着含气饱和度变化而变化的关系式,并将之应用到致密砂岩层含气饱和度的评价中,评价效果良好.这为导电性评价饱和度失效时,评价致密砂岩气层提供了新的方法.     

岩石弹性波速度和饱和度、孔隙流体分布的关系

在实验室对6种砂岩进行了连续的进水和失水实验. 测 量了两个过程的纵波速度VP、横波速度VS进水和失水速率随饱和度SW的 变化；分析了低饱和度时流体对岩石弹性性质的影响. 实验表明，进水和失水过程显示不同 的纵、横波速度与饱和度关系，速度不仅与饱和度有关，还与不同饱和阶段的孔隙流体分布 有关，而且也是水和岩石骨架之间的物理及化学作用所致.     

含孔隙、裂隙地层随钻多极子声波测井理论

储层岩石中普遍存在孔隙与裂隙,对钻井中的测井声波产生重要影响.基于孔、裂隙介质弹性波理论,导出了随钻声波测井的井孔声场表达式.据此考察了地层裂隙密度与含气饱和度的变化时井孔内随钻多极子模式波（斯通利波、弯曲波和螺旋波）的速度、衰减与灵敏度以及地层纵、横波的响应特征.裂隙密度与含气饱和度对模式波的速度频散与衰减都有影响,且两参数的值越大,影响越大.具体来说,速度对裂隙密度更敏感,而衰减对含气饱和度更敏感.具有"艾里相"特征的随钻偶极和四极子波在地层含气时产生强烈衰减,可以作为判断地层含气的一个明显指示.理论模拟与实际测井数据分析结果符合较好.     

干燥、饱油和饱水条件下砂岩地震波速的实验研究

岩石的地震波速度是浅部地层地下识别和区域构造研究的基础.哈密地区是我国重要的产油区域之一.本文利用Autolab2000岩石物性测试仪器,研究了0~200 MPa(约0~7000 m地下深度)下干燥、饱油与饱水三种状态时的砂岩地震波速度,得到了四组砂岩样品在三种状态下的纵横波速度与压力的拟合关系式.实验发现:在三种不同状态下,砂岩样品的纵横波速度都与压力呈对数关系;对于纵波,干燥下的波速明显小于饱油与饱水,但是饱油与饱水两种状态下岩石的纵波速度差异很小,饱水时的纵波速度略大于饱油;对于横波,低压下三种状态的地震波速度基本没有差异,在高压下,饱油与饱水样品的横波速度明显小于干燥样品.     

不同围压下孔隙度不同的干燥及水饱和岩样中的纵横波速度及衰减

选择具有不同孔隙度的三种岩石样品,在最高达600MPa （干燥样品）或300MPa （水饱和样品）的不同围压条件下,同时测量了在其中传播的纵、横波的速度及衰减。对于低孔隙度的花岗岩,干燥和水饱和样品的 Q 值几乎没有差别,但与干燥样品相比,水饱和样品中的纵波速度较高而横波速度稍低。对于中等孔隙度的杂砂岩,干燥样品和水饱和样品的波速和 Q 值及其随围压的变化有明显的不同。在高孔隙度的砂岩中这种不同更加显著。综合分析同时测得的纵、横波速度和 Q 值可以发现,当围压增加时,低孔隙度的花岗岩中同体应变相关的能量损失与同剪切应变相关的能量损失之比减小,但在中等孔隙度的杂砂岩和高孔隙度的砂岩中这一比值增大;同时,水饱和样品中的这一比值要比干燥样品中的大,而且它们之间的差别同样品的孔隙度正相关。     

叠前地震反演技术在苏里格气田的应用

苏里格气田属于我国特大型气田之一,地震反演技术广泛应用在气田勘探开发阶段.对研究区已有的资料进行岩石物理分析发现,纵波阻抗不能够识别目的层段砂岩、泥岩以及含气层.为了克服这一困难,采用叠前反演技术对盒_8-山_1段岩性气藏进行了刻画.在测井资料质控下以分角度叠加数据体作为输入,可以输出阻抗剖面以及纵横波速度比、泊松比等岩石弹性参数,综合判储层的岩性、物性及含气性.研究结果表明:(1)纵波阻抗不能区分砂泥岩以及含气砂岩,砂岩含气后,纵波阻抗明显降低,且分偏移距叠加数据体的振幅随偏移距的增加而增加,属于第三类AVO;(2)利用Xu-White模型对缺失横波资料进行反演,反演横波与全波测井实测横波对比发现相似度极高;(3)从反演结果来看,砂岩含气后横波阻抗不变,可以指示砂岩,速度比和泊松比显示异常小值,可以刻画含气砂岩.实钻证明,叠前反演技术为最终的井位优选和储层评价提供了可靠的依据.     

砾岩储层地震波传播方程:三重孔隙结构模型

针对砾岩储层的砂、砾、泥三重孔隙结构特征,本文分析砾岩孔隙区域、砂岩孔隙区域以及泥岩孔隙区域相互之间的孔隙流体流动机制,将静态的砾岩骨架本构方程与动态的孔隙流体运动方程联立,提出了复杂砾岩储层的弹性波传播理论方程.采用实测砾岩储层参数,在算例中与双重孔隙介质理论进行对比分析,验证了本文理论方程的合理性;基于三重孔隙介质模型,分析不同储层环境下纵波的传播特征,结果显示:随流体黏滞系数增大,在衰减-频率轴坐标系中,砾与砂、砂与泥孔隙区域间局域流导致的两个衰减峰向低频端移动,而Biot全局流导致的衰减峰向高频端移动;嵌入体尺寸及背景相介质渗透率的变化,主要影响纵波速度频散曲线沿频率轴左、右平移,不影响波速低频、高频极限幅值;嵌入体含量及孔隙度的变化改变了岩石干骨架的弹性、密度参数,不仅影响速度频散曲线沿频率轴平移,而且影响其上、下限幅值;砾包砂包泥三重孔隙介质模型所预测的衰减曲线中,低频段"第一个衰减峰"主要由砾岩孔隙区域与砂岩孔隙区域之间的局域流导致,中间频段"第二个衰减峰"主要由砂岩孔隙区域与泥岩孔隙区域之间的局域流导致,超声频段"第三个衰减峰"由Biot全局流导致.对慢纵波传播特征的分析显示,砂岩骨架(局部孔隙度较大)内部的宏观孔隙流体流动造成的耗散明显强于砾岩与泥岩骨架.     

Effects of petrophysical parameters on attenuation and dispersion of seismic waves in the simplified poroelastic theory: Comparison between the Biot's theory and viscosity‐extended theory

The simplified macro‐equations of porous elastic media are presented based on Hickey's theory upon ignoring effects of thermomechanical coupling and fluctuations of porosity and density induced by passing waves. The macro‐equations with definite physical parameters predict two types of compressional waves (P wave) and two types of shear waves (S wave). The first types of P and S waves, similar to the fast P wave and S wave in Biot's theory, propagate with fast velocity and have relatively weak dispersion and attenuation, while the second types of waves behave as diffusive modes due to their distinct dispersion and strong attenuation. The second S wave resulting from the bulk and shear viscous loss within pore fluid is slower than the second P wave but with strong attenuation at lower frequencies. Based on the simplified porous elastic equations, the effects of petrophysical parameters (permeability, porosity, coupling density and fluid viscosity) on the velocity dispersion and attenuation of P and S waves are studied in brine‐saturated sandstone compared with the results of Biot's theory. The results show that the dispersion and attenuation of P waves in simplified theory are stronger than those of Biot's theory and appear at slightly lower frequencies because of the existence of bulk and shear viscous loss within pore fluid. The properties of the first S wave are almost consistent with the S wave in Biot's theory, while the second S wave not included in Biot's theory even dies off around its source due to its extremely strong attenuation. The permeability and porosity have an obvious impact on the velocity dispersion and attenuation of both P and S waves. Higher permeabilities make the peaks of attenuation shift towards lower frequencies. Higher porosities correspond to higher dispersion and attenuation. Moreover, the inertial coupling between fluid and solid induces weak velocity dispersion and attenuation of both P and S waves at higher frequencies, whereas the fluid viscosity dominates the dispersion and attenuation in a macroscopic porous medium. Besides, the heavy oil sand is used to investigate the influence of high viscous fluid on the dispersion and attenuation of both P and S waves. The dispersion and attenuation in heavy oil sand are stronger than those in brine‐saturated sandstone due to the considerable shear viscosity of heavy oil. Seismic properties are strongly influenced by the fluid viscosity; thus, viscosity should be included in fluid properties to explain solid–fluid combination behaviour properly.     

砂岩在不同条件下的强度变形特点和P波速度特征

本文介绍了砂岩样品在干燥和饱和状态下,沿平行层理和垂直层理两个不同方向进行单轴加载时的抗压强度、变形特点和垂直于应力方向的P波走时的变化。结果表明,水对砂岩强度、P波速度的影响较大;具有原生层理构造的岩石样品的强度、变形和P波速度显示一定的方向性。所得结果对水库地震、工程地震、矿山开采及地震预报有一定的参考价值。     

基于Kelvin-Voigt黏弹性骨架的含非饱和流体孔隙介质BISQ模型(英文)

本文综合考虑了在波传播过程中孔隙介质的三种重要力学机制——"Biot流动机制一squirt流动机制-固体骨架黏弹性机制",借鉴等效介质思想,将含水饱和度引入波动力学控制方程,并考虑了不同波频率下孔隙流体分布模式对其等效体积模量的影响,给出了能处理含粘滞性非饱和流体孔隙介质中波传播问题的黏弹性Biot/squirt(BISQ)模型。推导了时间-空间域的波动力学方程组,由一组平面谐波解假设,给出频率-波数域黏弹性BISQ模型的相速度和衰减系数表达式。基于数值算例分析了含水饱和度、渗透率与频率对纵波速度和衰减的影响,并结合致密砂岩和碳酸盐岩的实测数据,对非饱和情况下的储层纵波速度进行了外推,碳酸盐岩储层中纵波速度对含气饱和度的敏感性明显低于砂岩储层。     

Acoustic and petrophysical relationships in low-shale sandstone reservoir rocks

This paper describes the measurements of the acoustic and petrophysical properties of two suites of low‐shale sandstone samples from North Sea hydrocarbon reservoirs, under simulated reservoir conditions. The acoustic velocities and quality factors of the samples, saturated with different pore fluids (brine, dead oil and kerosene), were measured at a frequency of about 0.8 MHz and over a range of pressures from 5 MPa to 40 MPa. The compressional‐wave velocity is strongly correlated with the shear‐wave velocity in this suite of rocks. The ratio V_P/V_S varies significantly with change of both pore‐fluid type and differential pressure, confirming the usefulness of this parameter for seismic monitoring of producing reservoirs. The results of quality factor measurements were compared with predictions from Biot‐flow and squirt‐flow loss mechanisms. The results suggested that the dominating loss in these samples is due to squirt‐flow of fluid between the pores of various geometries. The contribution of the Biot‐flow loss mechanism to the total loss is negligible. The compressional‐wave quality factor was shown to be inversely correlated with rock permeability, suggesting the possibility of using attenuation as a permeability indicator tool in low‐shale, high‐porosity sandstone reservoirs.     

Velocity and attenuation in partially saturated rocks: poroelastic numerical experiments

We use a poroelastic modelling algorithm to compute numerical experiments on wave propagation in a rock sample with partial saturation using realistic fluid distribution patterns from tomography scans. Frequencies are in the range 10 to 500 kHz. The rock is a homogeneous isotropic sandstone partially filled with gas and water, which are defined by their characteristic values of viscosity, compressibility and density. We assume no mixing and that the two different pore-fills occupy different macroscopic regions. The von Kármán self-similar correlation function is used, employing different fractal parameters to model uniform and patchy fluid distributions, respectively, where effective saturation is varied in steps from full gas to full water saturation. Without resorting to additional matrix–fluid interaction mechanisms, we are able to reproduce the main features of the variation in wave velocity and attenuation with effective saturation and frequency, as those of published laboratory experiments. Furthermore, the behaviour of the attenuation peaks versus water saturation and frequency is similar to that of White's model. The conversion of primary P-wave energy into dissipating slow waves at the heterogeneities is shown to be the main mechanism for attenuating the primary wavefield. Fluid/gas patches are shown to affect attenuation more than equivalent patches in the permeability or solid-grain properties.     

有效应力变化对致密砂岩孔隙结构及弹性波响应的影响规律

致密砂岩气藏具有裂缝发育和有效应力高的特征,研究不同有效压力下孔、裂隙介质地震波传播特征,有利于地震解释与地下储层的识别.但是前人的研究较少考虑岩石内部微观孔隙结构特征与孔隙、裂隙间流体流动的关系.本文首先通过选取四川盆地典型致密砂岩岩样,在不同有效压力下对岩石样本进行超声波实验测量.然后基于实验测得的纵、横波速度进行裂隙参数反演,得到不同有效压力下致密砂岩样本的裂隙孔隙度.再将裂隙孔隙度和样本岩石物理参数代入双重孔隙介质模型,模拟得到不同有效压力下饱水致密砂岩样本纵横波速度频散和衰减的变化规律.结果表明模型预测的速度频散曲线与纵波速度实验测量结果能够较好的吻合.最后统计分析了致密砂岩裂隙参数,得到了致密砂岩储层裂隙参数随有效压力及孔隙度变化特征.依据实际岩石物理参数建立模型,其裂隙参数三维拟合结果能够较好描述致密砂岩裂隙结构与孔隙度、应力的关联,可为实际地震勘探中预测储层裂缝性质提供基础依据.     

不同围压和流体饱和状态下致密砂岩弹性各向异性特征

为研究致密砂岩声波速度及其各向异性随围压的变化规律以及不同流体饱和状态下的弹性各向异性特征,钻取了不同方向的岩心并在实验室超声波频率下对致密砂岩的声学特性进行了测量,分别给出干燥和饱和水状态下,不同方向样品纵横波速度、刚性系数以及各向异性系数随围压的变化规律,并对实验结果进行了分析讨论.实验结果表明致密砂岩纵横波速度、纵横波速度比以及刚性系数均随围压增加而增加,但其在不同饱和状态下的变化率却截然不同;纵横波速度比、各向异性系数在饱和水状态下变化规律不明显,表明孔隙流体的存在对于岩石物理性质有着非常重要的影响.这方面的实验工作不但对于考察不同流体性质对致密岩石弹性各向异性影响是必要的,而且有助于致密砂岩油水和气层的识别.     

Propagation of guided waves in a fluid layer bounded by two viscoelastic transversely isotropic solids

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.     

The influence of mesoscopic flow on the P-wave attenuation and dispersion in a porous media permeated by aligned fractures

In sedimentary rocks attenuation/dispersion is dominated by fluid-rock interactions. Wave-induced fluid flow in the pores causes energy loss through several mechanisms, and as a result attenuation is strongly frequency dependent. However, the fluid motion process governing the frequency dependent attenuation and velocity remains unclear. We propose a new approach to obtain the analytical expressions of pore pressure, relative fluxes distribution and frame displacement within the double-layer porous media based on quasi-static poroelastic theory. The dispersion equation for a P-wave propagating in a porous medium permeated by aligned fractures is given by considering fractures as thin and highly compliant layers. The influence of mesoscopic fluid flow on phase velocity dispersion and attenuation is discussed under the condition of varying fracture weakness. In this model conversion of the compression wave energy into Biot slow wave diffusion at the facture surface can result in apparent attenuation and dispersion within the usual seismic frequency band. The magnitude of velocity dispersion and attenuation of P-wave increases with increasing fracture weakness, and the relaxation peak and maximum attenuation shift towards lower frequency. Because of its periodic structure, the fractured porous media can be considered as a phononic crystal with several pass and stop bands in the high frequency band. Therefore, the velocity and attenuation of the P-wave show an oscillatory behavior with increasing frequency when resonance occurs. The evolutions of the pore pressure and the relative fluxes as a function of frequency are presented, giving more physical insight into the behavior of P-wave velocity dispersion and the attenuation of fractured porous medium due to the wave-induced mesoscopic flow. We show that the specific behavior of attenuation as function of frequency is mainly controlled by the energy dissipated per wave cycle in the background layer.