震电效应研究在资源勘探中的应用前景

石油，天然气和水的储层主要为含流体多孔介质。由于油气和水资源勘探的日益增长的需要，与含流体多孔介质密切相关的震电效应研究在我国得到了迅速发展。针对声电测井探测渗透率，地震波传播的损耗及其控制，天然电磁波与电磁场的产生机制及其利用等问题，已对第一类震电效应（震阻效应或I效应），第二类震电效应（流动电势效应或E效应）以及充放电（激发极化）效应，开展了理论和实验研究，取得了相当大的进展。随着油气勘探二次创业的到来，将为震电效应在资源勘探中的应用带来巨大的机遇和挑战。     

油水两相饱和储层中平面震电波场响应特性

现有的孔隙介质震电理论缺乏针对含油储层震电耦合的数学模型及定量模拟,制约了该方法在含油储层中的推广应用.本文将非饱和孔隙介质中弹性波动理论与含油储层中动电耦合理论及麦克斯韦电磁理论相结合,建立了描述油水两相饱和储层中震电耦合波的数学方法,定量模拟了含油储层中平面震电波场响应特性,并探讨了储层参数对震电波场响应的影响.研究结果表明:油水两相饱和储层中震电耦合产生四种震电耦合波,震电横波、震电纵波P1、P2和P3波;震电波场响应具有频散特性,频率增大,震电纵波P2和P3波传播速度显著增大,震电波衰减常数均增大;相同频率下,震电纵波P2波电场强度及电流密度与固相速度比值的模值相比其它三种震电波的均较大,说明其激发电场和电流能力较强;震电波场响应受到宏观储渗参数的影响,储层孔隙度增大,震电波的传播速度均减小,三种震电纵波的衰减常数均增大,且震电横波和震电纵波P1波的电场强度与固相速度比值的模值均增大,震电纵波P2和P3波的均减小;储层渗透率增大,震电波的传播速度均增大,震电横波的衰减常数、电场强度与固相速度比值的模值亦增大,而三种震电纵波的则相反;含水饱和度增大,震电横波、震电纵波P1(低频时)和P2波的传播速度均减小,衰减常数、电场强度及电流密度与固相速度比值的模值均增大,震电纵波P3波的则相反;震电波响应电场强度及电流密度与固相速度比值的相位在高频时出现频散现象,同样受到储层参数的影响.     

声电效应测井的有限差分模拟

本文研究声电效应测井波场的有限差分模拟算法.忽略井外地层中诱导电磁场对孔隙弹性波的影响,将求解动电耦合波方程组的问题解耦,先计算孔隙弹性波,再计算其诱导电磁场.基于轴对称柱坐标系下的速度-应力交错网格,采用时域有限差分计算井孔流体声波和井外地层孔隙弹性波.将电磁场近似看作似稳场,基于轴对称柱坐标系下的5点式有限差分网格,求解不同时刻的电位Poisson方程,计算诱导电场.结果表明:本文算法可准确模拟频率6.0 kHz的声电效应测井全波;在声波测井频率范围内,电导率、动电耦合系数和动态渗透率的低频近似对伴随电磁场的计算影响不大;地层水平界面导致伴随反射斯通利波的电场和显著的界面电磁波,后者对于探测地层界面具有潜在的应用价值.     

饱和岩石的动态渗透率和动电耦合系数解析式

动态渗透率和动电耦合系数是描述岩石中渗流波动和弹性-电磁耦合波效应的重要参数.本文基于毛细管束模型,提出了流体饱和孔隙介质的动态渗透率和动电耦合系数的解析表达式和简化表达式,并通过与前人近似式结果的对比,分析了不同表达式的合理性和适用性.在此基础上,理论分析了孔隙几何形状和孔径分布对渗透率和动电耦合系数的频率响应以及井孔震电耦合波场的影响.研究结果表明:当认为孔道均匀且达西渗透率、孔隙度和弯曲度恒定时,孔隙几何形状的影响很小,可以忽略,而前人的近似式高估了孔隙几何形状的影响;孔径分布的影响显著,随着孔径分布的增大,渗透率的临界频率显著减小,动电耦合系数的临界频率显著增加,震电测井的斯通利波及其伴随电场幅度显著增大.     

横观各向同性饱和土的基本方程组

两相饱和多孔介质的基本方程组和计算参数的选取在一定程度上是混乱的.本文利用连续介质力学理论，结合空间平均化方法，根据应力-应变关系、运动学关系、连续性方程及广义Darcy定律，建立了横观各向同性液体饱和多孔介质的基本方程组；通过将该基本方程组与Biot理论的基本方程组进行比较，确定了Biot方程组中的弹性常数Bi与弹性常数cij的关系，并得到了确定Biot参数mi和ri的计算公式——Biot参数与渗透率、孔隙率及黏性系数的关系；最后对几种特殊情形进行了讨论，给出了简化方程组.     

求解双相和黏弹性介质波传播方程的间断有限元方法及其波场模拟

间断有限元（Discontinuous Galerkin：DG）方法具有低数值频散、网格剖分灵活、能模拟地震波在复杂介质中传播等优点.因此,本文将一种新的DG方法推广到双相和黏弹性等复杂介质的地震波场模拟,发展了求解Biot弹性波方程和D'Alembert介质波动方程的DG方法.首先通过引入辅助变量将Biot双相介质弹性波方程和D'Alembert介质波动方程转化为关于时间-空间的一阶偏微分方程组,然后对该方程组进行DG空间离散,得到半离散化的常微分方程组.最后,对此常微分方程组,应用加权的Runge-Kutta格式进行时间推进计算.数值结果表明,DG方法可以有效地求解Biot双相介质弹性波方程和D'Alembert介质波动方程,并能很好地压制因离散求解波动方程而产生的数值频散,获得清晰的各种地震波震相.     

大姚6级间歇双震中余震与前震的地震波识别

分析了2003年大姚6级间歇双震序列中，第一主震余震与第二主震前震的地震波动力学、波形特征。提出了当第一主震序列中“大头波”和“小头波”两类波形的P波初动一致时，分类、分时段动态追踪P波和S波的振幅比值呈线性的一组，就可识别第二主震的前震，追踪前震波形变化。将其与岩样加压声发射试验结果中类似的前震波形特征做了相互印证，同时分析了初动方向相反的震例：1976年盐源-宁蒗6级间歇双震序列，指出可以初动方向相同、P波与S波振幅比值呈线性的情况为两个双震第二主震前震的判定特征。     

砂岩样品的震电效应实验研究（英文）

地震波场和电磁场耦合产生的震电效应与储层物性参数有关,含流体孔隙介质中震电效应的研究有助于更好的描述储层特性。本文我们对饱和砂岩样品中的震电效应进行了实验研究,构建了一套震电测量装置。利用此测量装置记录了在声波激励下砂岩样品中产生的震电转换信号,观测得到了砂岩界面产生的震电信号的衰减特性,在此基础上进一步研究了震电信号与砂岩物理参数之间的关系。在震电效应的实验中发现尽量减小参考电位与震电信号扰动区的基准电位之间的电位差是保证震电实验测量精确性的关键点,能够显著提高震电信号的可探测性。震电测量结果证实了地震波在含流体孔隙介质中传播时,能诱导震电耦合,同时给出了震电界面响应的特点。震电信号振幅随着波源与岩样距离的增加呈线性衰减,随着接收电极与岩样界面距离的增加呈指数衰减。不同渗透率砂岩样品中产生的震电响应结果表明震电响应的强弱与样品渗透率成正相关,震电效应可以作为研究储层渗透率的一种新方法。     

矿体的动电辐射

众所周知,岩体内弹性振动的传播伴随着激发各种性质的电磁波,发生这种现象是由于第二类地震电效应、动电效应和压电效应之故。取一级近似时,前两种效应的特征是,弹性波与电磁波的频率一致,而且弹性波与电磁波的振幅是线性关系。含有石英岩体的压电效应也具有上述特征。在激发石英脉或石英压电晶体的矿体时,由于出现共振现象,电磁波的频谱可能与弹性波的频谱有显著区别。在记录含有闪锌矿岩体的压电效应时,没有发现电磁波与弹性波的频率有差别。在采取井下地球物理勘探压电方法工作时,查明在距离产生弹性振动的爆点几十米处,用重为十分之几到几公     

震电效应原理和初步实验结果

从电化学理论、薄膜效应以及浓差极化，解释了震电效应的基本原理.通过室内沙槽和岩芯标本实验，发现了震电信号，且在砂土上的震电信号比粘土上的大；含石油岩芯标本上的震电效应信号比含水岩芯标本上的强.通过室外实验，也已经测量到可信的震电效应信号，从而为石油测井继续研究提供了实验数据.     

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.     

Numerical Simulation of the Effect of a DC Electric Field on Seismic Wave Propagation with the Pseudospectral Time Domain Method

We have modeled the effect of a direct current (DC) electric field on the propagation of seismic waves by the pseudospectral time domain (PSTD) method, based on a set of governing equations for the poroelastic media. This study belongs to the more general term of the seismoelectric coupling effect. The set of physical equations consists of the poroelastodynamic equations for the seismic waves and the Maxwell's equations for the electromagnetic waves; the magnitude of the seismoelectric coupling effect is characterized by the charge density, the electric conductivity, the Onsager coefficient, a function of the dielectric permittivity, the fluid viscosity, and the zeta potential. The poroelastodynamic vibration of a solid matrix generates an electric oscillation with the form of streaming current via the fluctuation of pore pressure. Meanwhile, fluctuating pore pressure also causes oscillatory variation of the electric resistivity of the solid matrix. The simulated poroelastic wave propagation and electric field variation with an existing background DC electric field are compared with the results of a physical experiment carried out in an oilfield. The results show that the DC electric field can significantly affect the propagating elastic energy through the seismoelectric coupling in a wide range of the seismic frequency band.     

Dependence of borehole shear‐horizontal‐wave seismoelectric response on soil textures

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.     

双声源激发随钻测井声电耦合波理论模拟

随钻单极源声波测井中,由于钻铤模式波的干扰而使地层纵波速度的测量变得困难.孔隙地层的声电转换物理效应给我们提供了通过测量转换电信号实现声学参数测量的可能性.针对随钻声电测井,采用Pride声电耦合方程组描述井外孔隙地层的声电耦合波场,考虑随钻环境条件下的边界条件,采用实轴积分法计算出了随钻声电测井瞬态响应的波场.计算结果表明,声电转换比与电缆声电测井量级相同,也说明随钻环境下声电效应是可应用的.但是,从得到的电场波形图中可以观察到,钻铤模式波成分虽有压制,但仍然存在.为了削弱钻铤模式波,鉴于钻铤的声波速度已知,我们尝试利用双发射源测井方法,通过控制源间距及合适的发射延迟时间对钻铤模式波进行进一步压制.结果表明,采用双源后的井内转换声场和电场波形中,钻铤模式波被有效地抑制,残余钻铤波的相对振幅明显减小,压制效果在电场波形中尤为明显,地层波的信噪比显著增强,有利于地层纵波速度的提取.     

Experimental measurements of the streaming potential and seismoelectric conversion in Berea sandstone

The streaming potential across a porous medium is induced by a fluid flow due to an electric double layer between a solid and a fluid. When an acoustic wave propagates through a porous medium, the wave pressure generates a relative movement between the solid and the fluid. The moving charge in the fluid induces an electric field and seismoelectric conversion. In order to investigate the streaming potential and the seismoelectric conversion in the same rock sample, we conduct measurements with Berea sandstone saturated by NaCl solutions with different conductivities. We measure the electric voltage (streaming potential) across a cylindrical sample in NaCl solutions with different conductivities and under different pressures to determine the DC coupling coefficients. We also measure the seismoelectric signals induced by acoustic waves with a Berea sandstone plate at different frequencies and solution conductivities. The pressures of the acoustic waves are calibrated with a standard hydrophone (Brüel & 8103) at different frequencies (15–120 kHz). We calculate the quantitative coupling coefficients of the seismoelectric conversion at DC and at high frequencies with samples saturated by solutions with different conductivities. When the Berea sandstone sample is saturated by the NaCl solution with 0.32 mS/m in conductivity, for example, the DC and seismoelectric coupling coefficients at 15 kHz are 0.024 μV/Pa and 0.019 μV/Pa, respectively. The seismoelectric coupling coefficient is an important and helpful parameter for designing a seismoelectric tool. More experimental measurements of seismoelectric coupling coefficients in the frequency range of 100 Hz to 15 kHz are needed in the future.     

Seismoelectric numerical simulation in 2D vertical transverse isotropic poroelastic medium

Seismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary–secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ.     

多极源随钻动电测井波场特性实验研究

探索基于孔隙介质动电效应的随钻测井新方法是当前测井勘探领域的热点研究之一.本文针对随钻测井情况下的动(声)-电转换机理,在砂岩模型井中进行了多极源(单/偶/四极源)随钻动电测井实验研究,记录了井中声波激发动电转换波场的时域波形,给出了各分波的时间-速度图,并与多极源随钻声波测井数据进行对比,结果表明:钻铤波诱导的动电转换信号在随钻动电测井全波中的相对幅度显著降低,从而可准确提取到地层声波的传播速度,实现了利用随钻动电测井方法测量地层波速的目的,验证了随钻动电测井技术可有效抑制钻铤波的思想.本文还进一步分析了钻铤波的动电耦合特性,并结合有机玻璃模型井中随钻动电测井和无井孔模型下的随钻声波测量,研究了伴随钻铤波电场信号的传播特性和衰减规律,深入探讨了随钻动电测井全波中钻铤波被削弱的原因,并给出了定量的实验数据分析,为随钻动电测井理论模拟的解释提供有效实验数据支撑.     

随钻条件下井旁界面声电效应的辐射电磁波响应特征

孔隙地层中存在着动电耦合现象,弹性波作用在声阻抗或者电化学性质差异地层会产生辐射电磁波.本文探讨了随钻条件下,利用孔隙地层中的动电耦合效应探测井旁地质体的可行性.为此模拟了井外存在声阻抗差异和电化学差异界面时声波诱导的辐射电场响应特征.求出柱坐标下介质中声场和电场函数表达式,由此计算并比较了均匀介质和弹性差异界面情况下井中接收到的电场.发现随钻条件下,井外的弹性差异界面会产生以光速传播的辐射电磁波.该电磁波反映了井外地质信息,并先于井中直达声波的伴随电磁场到达接收器,因而可以直接观测到.此外,还发现界面辐射电磁波可以用来探测油、水等电化学性质差异大而弹性阻抗差异小的界面;声源频率以及界面两侧地层性质差异程度是辐射电磁波幅度的影响因素.     

Immiscible two-phase fluid flows in deformable porous media

Macroscopic differential equations of mass and momentum balance for two immiscible fluids in a deformable porous medium are derived in an Eulerian framework using the continuum theory of mixtures. After inclusion of constitutive relationships, the resulting momentum balance equations feature terms characterizing the coupling among the fluid phases and the solid matrix caused by their relative accelerations. These terms, which imply a number of interesting phenomena, do not appear in current hydrologic models of subsurface multiphase flow. Our equations of momentum balance are shown to reduce to the Berryman–Thigpen–Chen model of bulk elastic wave propagation through unsaturated porous media after simplification (e.g., isothermal conditions, neglect of gravity, etc.) and under the assumption of constant volume fractions and material densities. When specialized to the case of a porous medium containing a single fluid and an elastic solid, our momentum balance equations reduce to the well-known Biot model of poroelasticity. We also show that mass balance alone is sufficient to derive the Biot model stress–strain relations, provided that a closure condition for porosity change suggested by de la Cruz and Spanos is invoked. Finally, a relation between elastic parameters and inertial coupling coefficients is derived that permits the partial differential equations of the Biot model to be decoupled into a telegraph equation and a wave equation whose respective dependent variables are two different linear combinations of the dilatations of the solid and the fluid.     

饱和多孔微极介质的波动方程及其势函数方程

土是由一定尺寸大小颗粒所构成的多孔介质,具有明显的颗粒特性,当土颗粒间的孔隙被流体（如水或油）充满时则成为饱和土.利用微极理论和Biot波动理论的研究成果,把饱和土中多孔固体骨架部分近似地视为微极介质,孔隙中的流体部分视为质点介质,获得饱和多孔微极介质的弹性波动方程.借鉴Greetsma理论,建立了饱和多孔微极介质弹性本构方程力学参数与相应单相介质弹性参数的相互关系,使饱和多孔微极介质弹性波动方程中的物理参数具有明确的物理意义,易于在试验中确定.运用场论理论把饱和多孔微极介质的波动方程简化为势函数方程,建立了饱和多孔微极介质中五种弹性波的弥散方程,数值分析了五种简谐体波在无限饱和多孔微极介质中的传播特性. 结果表明,P1波、P2波和剪切S1波的波速弥散曲线与经典饱和多孔介质基本相同,当频率小于临界频率ω0时旋转纵波θ波和横波S2波不存在,当频率大于临界频率ω0时,θ波和S2波的传播速度随频率增加而减小.