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1.
The article discusses the excitation of transient induced polarization responses using current and voltage sources. The first method has found a wide application in induced polarization surveys and—directly or indirectly—in the theory of the induced polarization method. Typically, rectangular current pulses are injected into the earth via grounding electrodes, and decaying induced polarization voltage is measured during the pauses between pulses. In this case, only the secondary field is recorded in the absence of the primary field, which is an important advantage of this method. On the other hand, since the current injected into the ground is fully controlled by the source, this method does not allow studying induced polarization by measuring the current in the transmitter line or associated magnetic field. When energising the earth with voltage pulses, the measured quantity is the transient induced polarization current. In principle, this method allows induced polarization studies to be done by recording the transmitter line current, the associated magnetic field, or its rate of change. The decay of current in a grounded transmitter line depends not only on the induced polarization of the earth but also on the polarization of the grounding electrodes. This problem does not occur when induced polarization transients in the earth are excited inductively. A grounded transmitter line is a mixed‐type source; hence, for a purely inductive excitation of induced polarization transients, one should use an ungrounded loop, which is coupled to the earth solely by electromagnetic induction. 相似文献
2.
Comparative review of theoretical models for elastic wave attenuation and dispersion in partially saturated rocks 总被引：1，自引：0，他引：1
J. Toms T.M. Müller R. Ciz B. Gurevich 《Soil Dynamics and Earthquake Engineering》2006,26(6-7):548-565
Saturation of porous rocks with a mixture of two fluids (known as partial saturation) has a substantial effect on the seismic waves propagating through these rocks. In particular, partial saturation causes significant attenuation and dispersion of the propagating waves, due to wave-induced fluid flow. Such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids. As partial fluid saturation can occur on different length scales, attenuation due to wave-induced fluid flow is ubiquitous. In particular, mesoscopic fluid flow due to heterogeneities occurring on a scale greater than porescale, but less than wavelength scale, is responsible for significant attenuation in the frequency range from 10 to 1000 Hz.Most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a periodic/regular way. In 1D this corresponds to periodically alternating layering, in 3D as periodically distributed inclusions of a given shape (usually spheres). All these models yield very similar estimates of attenuation and dispersion.Experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion. Therefore, theoretical models are required which would simulate the effect of more general and realistic fluid distributions.We have developed two theoretical models which simulate the effect of random distributions of mesoscopic fluid heterogeneities. The first model assumes that one fluid forms a random ensemble of spherical inclusions in a porous medium saturated by the other fluid. The attenuation and dispersion predicted by this model are very similar to those predicted for 3D periodic distribution. Attenuation (inverse quality factor) is proportional to ω at low frequencies for both distributions. This is in contrast to the 1D case, where random and periodically alternating layering shows different attenuation behaviour at low frequencies. The second model, which assumes a 3D continuous distribution of fluid heterogeneities, also predicts the same low-frequency asymptote of attenuation. However, the shapes of the frequency dependencies of attenuation are different. As the 3D continuous random approach assumes that there will be a distribution of different patch sizes, it is expected to be better suited to modelling experimental results. Further research is required in order to uncover how to relate the random functions to experimentally significant parameters. 相似文献
3.
在球坐标系下用直接求解孔隙弹性方程的方法计算了介观尺度下空间周期排列的White球状Patchy模型中纵波传播问题.首先对纵波的衰减和频散进行了计算,并引入了物理学上声子晶体原理来解释高频时纵波在White球状模型中传播的异常现象.在含水饱和度和速度关系的研究中发现,在低频段用等效流体理论和Gassmann理论估计流体Patchy饱和岩石中的纵波速度完全能够满足当前地震勘探的要求.随后的具有相同含气饱和度但有不同周期的Patchy模型研究结果表明,随着空间周期变大,低频的纵波频散变得明显,纵波衰减峰频率向低频移动,但峰值几乎不变.最后,对单元外层含水中心含油的White球状Patchy模型和中心含气White球状Patchy模型进行研究、对比,发现孔隙流体流动对孔隙介质中的纵波频散、衰减影响显著.另外,在具体数值求解过程中用缩减方程组规模的方法解决了线性方程组严重病态得不到正确结果的问题. 相似文献
4.
Ander Guinea Elisabet Playà Lluís Rivero Mahjoub Himi Ricard Bosch 《Surveys in Geophysics》2010,31(6):557-580
Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum
mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered
than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with
geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological
composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response
of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations,
laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain
the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay
mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power
supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located
in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum
rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field
examples. A geoelectrical classification of gypsum rocks defining three types of gypsum rocks has been elaborated: (a) Pure
Gypsum Rocks (>75% of gypsum content), (b) Transitional Gypsum Rocks (75–55%), and (c) Lutites and Gypsum-rich Lutites (<55%).
From the economic point of view, the Pure Gypsum Rocks, displaying a resistivity value of >800 ohm.m, can be exploited as
industrial rocks. The methodology used could be applied in other geoelectrical rock studies, given that this relationship
between the resistive particles embedded within a conductive matrix depends on the connectivity of the matrix particles. 相似文献
5.
The inversion of density structure by graphic processing unit (GPU) and identification of igneous rocks in Xisha area 
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下载免费PDF全文 Organic reefs, the targets of deep-water petroleum exploration, developed widely in Xisha area. However, there are concealed igneous rocks undersea, to which organic rocks have nearly equal wave impedance. So the igneous rocks have become interference for future exploration by having similar seismic reflection characteristics. Yet, the density and magnetism of organic reefs are very different from igneous rocks. It has obvious advantages to identify organic reefs and igneous rocks by gravity and magnetic data. At first, frequency decomposition was applied to the free-air gravity anomaly in Xisha area to obtain the 2D subdivision of the gravity anomaly and magnetic anomaly in the vertical direction. Thus, the distribution of igneous rocks in the horizontal direction can be acquired according to high-frequency field, low-frequency field, and its physical properties. Then, 3D forward modeling of gravitational field was carried out to establish the density model of this area by reference to physical properties of rocks based on former researches. Furthermore, 3D inversion of gravity anomaly by genetic algorithm method of the graphic processing unit (GPU) parallel processing in Xisha target area was applied, and 3D density structure of this area was obtained. By this way, we can confine the igneous rocks to the certain depth according to the density of the igneous rocks. The frequency decomposition and 3D inversion of gravity anomaly by genetic algorithm method of the GPU parallel processing proved to be a useful method for recognizing igneous rocks to its 3D geological position. So organic reefs and igneous rocks can be identified, which provide a prescient information for further exploration. 相似文献
6.
The inversion of density structure by graphic processing unit （GPU） and identification of igneous rocks in Xisha area 总被引：1，自引：0，他引：1
Organic reefs, the targets of deep-water petroleum exploration, developed widely in Xisha area. However, there are concealed igneous rocks undersea, to which organic rocks have nearly equal wave impedance. So the igneous rocks have become interference for future exploration by having similar seismic reflection characteristics. Yet, the density and magnetism of organic reefs are very different from igneous rocks. It has obvious advantages to identify organic reefs and igneous rocks by gravity and magnetic data. At first, frequency decomposition was applied to the free-air gravity anomaly in Xisha area to obtain the 2D subdivision of the gravity anomaly and magnetic anomaly in the vertical direction. Thus, the distribution of igneous rocks in the horizontal direction can be acquired according to high-frequency field, low-frequency field, and its physical properties. Then, 3D forward modeling of gravitational field was carried out to establish the density model of this area by reference to physical properties of rocks based on former researches. Furthermore, 3D inversion of gravity anomaly by genetic algorithm method of the graphic processing unit(GPU) parallel processing in Xisha target area was applied, and 3D density structure of this area was obtained. By this way, we can confine the igneous rocks to the certain depth according to the density of the igneous rocks. The frequency decomposition and 3D inversion of gravity anomaly by genetic algorithm method of the GPU parallel processing proved to be a useful method for recognizing igneous rocks to its 3D geological position. So organic reefs and igneous rocks can be identified, which provide a prescient information for further exploration. 相似文献
7.
Jagdeo Singh 《Pure and Applied Geophysics》1970,82(1):165-188
Summary The present paper deals with the inverse polarization of rocks. At present there are two schools of thought to explain the inverse polarization. On the one hand, it is assumed that the geomagnetic field might have been reversed in those periods, when the rock formations took place. On the other it is advocated that it might be due to some intrinsic property of the rocks. To distinguish between the two theories, the author has studied the thermal demagnetization of a large number of rock samples from the Isle of Mull and has come to the conclusion that the inverse polarization is not due to an intrinsic property of the rocks as suggested byNéel, but to the reversal of the geomagnetic field. Some experimental details are also described in the paper. 相似文献
8.
《Journal of Applied Geophysics》2011,75(4):294-301
It is known that sedimentary rocks demonstrate velocity dispersion in the acoustic log frequency range. In this paper we have calculated the waveforms of sonic log for a borehole located in a viscoelastic medium. The acoustic field in the borehole has been obtained for acoustic multipole sources. To describe the viscoelastic properties of a rock we used the Cole–Cole model. This model describes the dispersion of acoustic wave velocities and quality factors in a wide frequency range. To solve the acoustic log direct problem we have applied the double integral Fourier transform (RAI method). The results obtained have shown the feasibility of S-wave velocity dispersion estimation from acoustic dipole waveform processing. 相似文献
9.
A polarizable sphere embedded in a conducting half-space can give rise to negative voltage transients in a coincident-loop time-domain electromagnetic system. Such transients have been observed in field situations. Our results are obtained from a model in which the contributions of the host rock, the currents in the sphere, and the interaction between the sphere and the host rock are separated and superposed. This model uses approximations to the integral equation solutions rather than finite-element or finite-difference approximations, and so allows very rapid computation. The theoretical demonstration suggests that interpretation of the negative voltage transients as a polarization response is valid, but more detailed interpretation of polarization properties may not be possible, because the superposition of the polarization response on the normal response depends strongly on the position of the target. 相似文献
10.
Wave‐induced fluid flow plays an important role in affecting the seismic dispersion and attenuation of fractured porous rocks. While numerous theoretical models have been proposed for the seismic dispersion and attenuation in fractured porous rocks, most of them neglect the wave‐induced fluid flow resulting from the background anisotropy (e.g. the interlayer fluid flow between different layers) that can be normal in real reservoirs. Here, according to the theories of poroelasticity, we present an approach to study the frequency‐dependent seismic properties of more realistic and complicated rocks, i.e. horizontally and periodically layered porous rock with horizontal and randomly orienting fractures, respectively, distributed in one of the two periodical layers. The approach accounts for the dual effects of the wave‐induced fluid flow between the fractures and the background pores and between different layers (the interlayer fluid flow). Because C33 (i.e., the modulus of the normally incident P‐wave) is directly related to the P‐wave velocity widely measured in the seismic exploration, and its comprehensive dispersion and attenuation are found to be most significant, we study mainly the effects of fracture properties and the stiffness contrast between the different layers on the seismic dispersion and attenuation of C33. The results show that the increasing stiffness contrast enhances the interlayer fluid flow of the layered porous rocks with both horizontal and randomly orienting fractures and weakens the wave‐induced fluid flow between the fractures and the background pores, especially for the layered porous rock with horizontal fractures. The modelling results also demonstrate that for the considered rock construction, the increasing fracture density reduces the interlayer fluid flow while improves the dispersion and attenuation in the fracture‐relevant frequency band. Increasing fracture aspect ratio is found to reduce the dispersion and attenuation in the fracture‐relevant frequency band only, especially for the layered porous rock with horizontal fractures. 相似文献
11.
12.
复电阻率测井在识别油水层的能力上优于常规电阻率测井,然而储层岩石复电阻率特性的微观机理还没有统一完整的解释和数学模拟方法,致使复电阻率测井技术的开发缺乏足够的理论基础.本文基于孔隙介质Pride电震耦合理论,结合谐变信号激励下渗流场与电流场的耦合理论,推导出一级近似条件下的Pride电震耦合理论.采用格林函数方法建立了一维电震波场的波动方程及其解.构造了双电极法测量储层岩石复电阻率的物理模型和数学模型,从理论上阐明了岩石复电阻率频散特性的微观机制与电震效应的关系,定量分析了储层岩石复电阻率频散特性的影响因素.数学模拟结果表明:储层岩石复电阻率的频散现象是在电震快纵波和电震慢纵波的共同作用下,由孔隙介质中的电渗流机制形成的;储层岩石的复电阻率随孔隙度的增大而减小,随渗透率的增大而增大,地层水矿化度的增加或阳离子交换量的增大使得同频率的复电阻率减小.慢纵波界面极化频率受孔隙度、渗透率和地层弹性模量的影响较大,而快纵波界面极化频率受地层弹性模量的影响较大. 相似文献
13.
Membrane polarization occurs in sediments with different surface area of capillaries (pores) and is regarded as a slow type of polarization. This phenomenon is the foundation of the well known methods of induced polarization (IP): time domain and frequency domain induced polarization. The characteristic parameters of induced polarization which are required for studying physical properties of rocks are measured in the laboratory. Data measured in the laboratory confirmed the distinctions of IP processes at time-on and time-off. Additionally linear dependence of voltage and applied current is not always observed. This paper presents the first step of studying: theoretical consideration for time-on and mathematical modeling of membrane polarization, ion concentrations of electrolyte in the pores of different models of pores space, and arising voltage. The problem of concentration of ions along the pores can be solved using the diffusion equation with specified initial and boundary conditions. Reduced boundary conditions for time-on show that transient concentrations at the boundaries are linear with time. It allows obtaining the analytical solution for this equation. Mathematical modeling has been performed for different combinations of pores. It is shown that if electrical current flows from the pores with greater transfer numbers to the pores with smaller transfer numbers, an excess of ions will be observed at this boundary. If the difference of transfer numbers is negative, there is a decrease in the concentration of ions at the vicinity of the boundary. This decrease will continue until the concentration at this boundary reaches zero. In this case the galvanic chain will be interrupted and electrical current flowing through the sample does not penetrate to this cell. The duration of the process of ions distribution in the pore and time of blockage t 0 is proportional to the radii of contacted pores and inversely proportional to the transfer number difference and square of the current flowing through this cell. It was shown by both laboratory measurement and field processes that induced polarization relates to low porous rocks with small transfer number differences. 相似文献
14.
A new method for the 2D inversion of induced polarization (IP) data in the time domain has been developed. The entire IP transients were observed and inverted into 2D Cole-Cole earth models, including resistivity, chargeability, relaxation time and the frequency constant. Firstly, a modified 1D time-domain electromagnetic algorithm was used to calculate the response of a layered polarizable ground. The transient signals were then inverted using the Marquardt method to derive the Cole-Cole parameters of each layer. However, model calculations showed that the EM effects could be neglected for the time range (>1 ms) and for the transmitter–receiver distances (<50 m) used in this study. Therefore, the induction effects were not considered for the solution of the 2D inverse problem and a DC solution was applied. An approximative forward algorithm was introduced in order to calculate the IP transients directly in the time domain and in order to speed up the inverse procedure. The approximation is highly accurate, and this is demonstrated by comparing the approximations with their exact solutions up to 3D. The inverse algorithm presented consists of two steps. The transient voltages of an array data set were inverted separately into a two-dimensional resistivity model for each time channel. The time-dependent resistivity of each cell was then interpreted as the response of a homogeneous half-space. In the 2D inversion algorithm, a 3D DC algorithm was used as a forward operator. The method only requires a standard 2D DC inversion and a homogenous half-space Cole-Cole inversion. The developed algorithm has been successfully applied to synthetic data sets and to a field data set obtained from a waste site situated close to Düren in Germany. 相似文献
15.
《Journal of Applied Geophysics》1999,41(1):31-47
The Idaho National Laboratory (INEL) Cold Test Pit (CTP) has been carefully constructed to simulate buried hazardous waste sites. An induced polarization (IP) survey of the CTP shows a very strong polarization and a modest resistivity response associated with the simulated waste. A three-dimensional (3-D) inversion algorithm based on the simultaneous iterative reconstruction technique (SIRT) and finite difference forward modelling has been applied to generate a subsurface model of complex resistivity. The lateral extents of the waste zone are well resolved. Limited depth extent is recognized, but the bottom of the waste appears too deep. With a modelling experiment, the intrinsic polarizability of the waste material is determined. Since IP is a technique for detection of diffuse occurrences of metallic material, this method holds promise as a method to distinguish buried waste from conductive soil material. 相似文献
16.
Transport in porous media is often characterized by the advection–dispersion equation, with the dispersion coefficient as the most important parameter that links the hydrodynamics to the transport processes. Morphological properties of any porous medium, such as pore size distribution, network topology, and correlation length control transport. In this study we explore the impact of correlation length on transport regime using pore-network modelling. Earlier direct simulation studies of dispersion in carbonate and sandstone rocks showed larger dispersion compared to granular homogenous sandpacks. However, in these studies, isolation of the impact of correlation length on transport regime was not possible due to the fundamentally different pore morphologies and pore-size distributions. Against this limitation, we simulate advection–dispersion transport for a wide range of Péclet numbers in unstructured irregular networks with “different” correlation lengths but “identical” pore size distributions and pore morphologies. Our simulation results show an increase in the magnitudes of the estimated dispersion coefficients in correlated networks compared to uncorrelated ones in the advection-controlled regime. The range of the Péclet numbers which dictate mixed advection–diffusion regime considerably reduces in the correlated networks. The findings emphasize the critical role of correlation length which is depicted in a conceptual transport phase diagram and the importance of accounting for the micro-scale correlation lengths into predictive stochastic pore-scale modelling. 相似文献
17.
D. A. Lockner J. D. Byerlee V. S. Kuksenko A. V. Ponomarev 《Pure and Applied Geophysics》1986,124(3):601-608
Measurements of charge separation in rock during stable and unstable deformation give unexpectedly large decay times of 50 sec. Time-domain induced polarization experiments on wet and dry rocks give similar decay times and suggest that the same decay mechanisms operate in the induced polarization response as in the relaxation of charge generated by mechanical deformation. These large decay times are attributed to electrochemical processes in the rocks, and they require low-frequency relative permittivity to be very large, in excess of 105. One consequence of large permittivity, and therefore long decay times, is that a significant portion of any electrical charge generated during an earthquake can persist for tens or hundreds of seconds. As a result, electrical disturbances associated with earthquakes should be observable for these lengths of time rather than for the milliseconds previously suggested. 相似文献
18.
A modified discrete element method is briefly introduced and used for modelling reservoir geomechanical response during fluid injection and depletion. The modified approach works as a continuum method until some local failure is initiated, after which it behaves like a discrete element method on a polygonal lattice. The method is advantageous for modelling fracture developments in rocks. It is applied here to synthetic models of two reservoirs taken from the North Sea (Gullfaks and Elgin‐Franklin). For Gullfaks, two cases of water injection were modelled, one with low horizontal effective stress and the other with low vertical effective stress. Vertical fractures are developed in the first case, whereas horizontal fractures are developed in the second case. This would not have been seen using traditional methods. Based on 4D seismics data for the Gullfaks field, one may envision that horizontal fractures could have been formed. The Elgin‐Franklin synthetic model is used to study various scenarios of changing stress field around the depleting reservoir. Based on 4D seismics data from this field, one may see changes that could be interpreted in terms of possible fault reactivation. 相似文献
19.
C. Cardaci S. Falsaperla P. Gasperini G. Lombardo W. Marzocchi F. Mulargia 《Bulletin of Volcanology》1993,55(8):596-603
Seismic data from the MVT-SLN sesmic station located 7 km from the summit area of Mt Etna volcano, which has been operating steadily for the last two decades, have been analysed together with the volcanic activity during the same period. Cross-correlation techniques are used to investigate possible relationships between seismic and volcanic data and to evaluate the statistical significance of the results. A number of significant correlations have been identified, showing that there is an evident relation between seismic events and flank eruptions, and a less clear relation with summit activity, which appears more linked to tremor rather than to the low-frequency events. Particularly interesting are the low-frequency events whose rate of occurrence increases, starting from 17 to 108 days, prior to the onset of the flank activity and are candidates for a useful precursor. On the other hand, a tendency towards the increase in both the duration and the occurrence rate of transients in the volcanic tremor was observed before the onset of summit eruptions. As a result of this study different stages in the volcanic activity of Mt Etna, represented by changes in the characteristics of the recorded seismic phenomena, are identified. 相似文献
20.
SAMI SOLIMAN MOHAMED 《Geophysical Prospecting》1970,18(Z1):654-665
During the last decade many hypotheses were suggested to explain the phenomenon of induced electrical polarization in ionic conductive media. The most reliable of these is Fredricksberg's. Fredricksberg (1962) supposed that the pore spaces of a rock is composed of successively narrow (active zones) and wide (inactive zones). He simulated these pore spaces by a synthetic material that has an extremely high resistance. The pore spaces were generally in tube forms which exhibited some constrictions. He saturated these tubes with an electrolyte of a given concentration. An electric current was passed through this model. He observed an induced polarization voltage after current interruption. He attributed the formation of this voltage to a concentration gradient which took place due to the presence of excess charges in the active zones. Fredricksberg introduced a parameter (9) which described the relation among the lengths and cross sectional areas of the wide zones, the number of ions within each zone after current interruption with the recorded polarizability. The aim of this work is to correlate Fredricksberg's parameter with a parameter determined for natural rocks and to show experimentally the validity of this hypothesis when applying for some varieties of sandstones and volcanic rocks. The new parameter will help to evaluate a relationship between the polarizability and the water-collecting properties of rocks. Herein, we used the tortuosity T of sandstone samples instead of the parameter φ which was used by Fredricksberg to represent the pore geometry within his model (tortuosity of the passes within the model). It was shown that both φ and T have the same relationship with the polarizability ν of the rock samples and if φ or T have very low or very high values the polarizability ν tends to its minimum value, i.e. the curve representing the relation between ν and T has a maximum point corresponding to an intermediate value of T. This result supports Fredricksberg's hypothesis and confirm his results on synthetic models. For volcanic rocks the formation factor F was used since it was difficult to determine the porosity of the samples and consequently to calculate the tortuosity T as for sandstone samples. Experimental results confirm those obtained from sandstone. The grain constituents of sandstone samples were represented on equilateral triangle and the magnitude of induced polarization ν of each sample was deduced and represented on this triangle. Equipolarizability values ν drawn on this triangle showed that TJ will increase as the silty fractions of the rock increase, where the center of this triangle (represents minimum porosity) has polarizability less than 0.25%. An attempt was made to determine the coefficient of anisotropy of volcanic rock samples using the induced polarization method. For this reason the polarizability was deduced by measuring the induced polarization voltage for two perpendicular directions in a fractured cubes of andesitic basalt samples the coefficient of anisotropy was found to be equal 1.18. 相似文献