scholarly journals Spectral Induced Polarization Survey with Distributed Array System for Mineral Exploration: Case Study in Saudi Arabia

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 769 ◽  
Author(s):  
Fouzan A. Alfouzan ◽  
Abdulrahman M. Alotaibi ◽  
Leif H. Cox ◽  
Michael S. Zhdanov
Keyword(s):  
Effective Medium Theory ◽  
Coupling Effect ◽  
Pilot Project ◽  
Drill Hole ◽  
Induced Polarization ◽  
Effective Medium ◽  
Inductive Coupling ◽  
Geothermal Resources ◽  
Spectral Induced Polarization ◽  
Distributed Array

The Saudi Arabian Glass Earth Pilot Project is a geophysical exploration program to explore the upper crust of the Kingdom for minerals, groundwater, and geothermal resources as well as strictly academic investigations. The project began with over 8000 km2 of green-field area. Airborne geophysics including electromagnetic (EM), magnetics, and gravity were used to develop several high priority targets for ground follow-up. Based on the results of airborne survey, a spectral induced polarization (SIP) survey was completed over one of the prospective targets. The field data were collected with a distributed array system, which has the potential for strong inductive coupling. This was examined in a synthetic study, and it was determined that with the geometries and conductivities in the field survey, the inductive coupling effect may be visible in the data. In this study, we also confirmed that time domain is vastly superior to frequency domain for avoiding inductive coupling, that measuring decays from 50 ms to 2 s allow discrimination of time constants from 1 ms to 5 s, and the relaxation parameter C is strongly coupled to intrinsic chargeability. We developed a method to fully include all 3D EM effects in the inversion of induced polarization (IP) data. The field SIP data were inverted using the generalized effective-medium theory of induced polarization (GEMTIP) in conjunction with an integral equation-based modeling and inversion methods. These methods can replicate all inductive coupling and EM effects, which removes one significant barrier to inversion of large bandwidth spectral IP data. The results of this inversion were interpreted and compared with results of drill hole set up in the survey area. The drill hole intersected significant mineralization which is currently being further investigated. The project can be considered a technical success, validating the methods and effective-medium inversion technique used for the project.

Cable arrangement to reduce electromagnetic coupling effects in spectral-induced polarization studies

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. A1-A5 ◽  
Author(s):  
Myriam Schmutz ◽  
Ahmad Ghorbani ◽  
Pierre Vaudelet ◽  
Amélie Blondel
Keyword(s):  
Coupling Effect ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Coupling Effects ◽  
Array Type ◽  
Spectral Induced Polarization ◽  
Computer Codes ◽  
Lateral Offset ◽  
Phase Angles

Spectral-induced polarization (SIP) is widely used for environmental and engineering geophysical prospecting and hydrogeophysics, but one major limitation concerns the electromagnetic (EM) coupling effect. The phase angles related to EM coupling may increase even at frequencies as low as 1 Hz, depending on the ground resistivity, the array type, and the geometry. Most efforts to understand and quantify the EM coupling problem (e.g., theory and computer codes) have been developed for dipole-dipole arrays. However, we used a Schlumberger array to acquire SIP data. We found that with this array, the use of an appropriate cable arrangement during data acquisition can reduce EM coupling effects in the same proportion as for the use of a dipole-dipole array, which is the pure response of the studied earth. To measure the influence of the cable layout, four cable configurations with the same electrode spacing were compared for modeling and experimental data. We discovered that the classical DC inline array was the worst one. As soon as the cables were arranged in another shape (triangle or rectangle), the coupling effect decreased significantly. The best configuration we checked was the rectangular one with an acquisition unit located at a lateral offset of 100 m from the electrode line, even if there was still some difference between the modeled and measured data.

Generalized effective-medium theory of induced polarization

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. F197-F211 ◽  
Author(s):  
Michael Zhdanov
Keyword(s):  
Mathematical Model ◽  
Arbitrary Shape ◽  
Effective Conductivity ◽  
Effective Medium Theory ◽  
Induced Polarization ◽  
Effective Medium ◽  
Matrix Composition ◽  
Medium Theory ◽  
Rock Formations ◽  
The Matrix

A rigorous physical-mathematical model of heterogeneous conductive media is based on the effective-medium approach. A generalization of the classical effective-medium theory (EMT) consists of two major parts: (1) introduction of effective-conductivity models of heterogeneous, multiphase rock formations with inclusions of arbitrary shape and conductivity using the principles of the quasi-linear (QL) approximation within the framework of the EMT formalism and (2) development of the generalized effective-medium theory of induced polarization (GEMTIP), which takes into account electromagnetic-induction (EMI) and induced polarization (IP) effects related to the relaxation of polarized charges in rock formations. The new generalized EMT provides a unified mathematical model of heterogeneity, multiphase structure, and the polarizability of rocks. The geoelectric parameters of this model are determined by the intrinsic petrophysical and geometric characteristics of composite media: the mineralization and/or fluid content of rocks and the matrix composition, porosity, anisotropy, and polarizability of formations. The GEMTIP model allows one to find the effective conductivity of a medium with inclusions that have arbitrary shape and electrical properties. One fundamental IP model of an isotropic, multiphase, heterogeneous medium is filled with spherical inclusions. This model, because of its relative simplicity, makes it possible to explain the close relationships between the new GEMTIP conductivity-relaxation model and an empirical Cole-Cole model or classical Wait’s model of the IP effect.

Modifying the generalized effective-medium theory of induced polarization model in compacted rocks

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. MR245-MR255
Author(s):  
Tong Xiaolong ◽  
Yan Liangjun ◽  
Xiang Kui
Keyword(s):  
Maxwell Equations ◽  
Effective Medium Theory ◽  
Induced Polarization ◽  
Effective Medium ◽  
High Resistivity ◽  
Hydraulic Permeability ◽  
Mineral Particle ◽  
Polarization Model ◽  
Rock Composition ◽  
Medium Theory

The generalized effective-medium theory of the induced polarization model (GEMTIP) is a mathematical-physical model derived from the Maxwell equations based on the effective-medium approach. Compared to the Cole-Cole model, the GEMTIP parameters are better related to the structural parameters of reservoir rocks, such as rock composition, mineral particle size, porosity, and specific surface; therefore, it can better describe the induced polarization (IP) characteristics of tight oil and gas reservoirs. However, GEMTIP is not suitable for high-resistivity perturbed media, and it does not account for interfacial polarization, which occurs between two media that share the same resistivity. Starting from the theoretical assumptions of the GEMTIP model, we derived an extended GEMTIP model (MGEMTIP) by adding an equivalent surface current term into the Maxwell equations for a heterogeneous medium. The complex resistivity parameters predicted by two models are compared through numerical simulation, and the results demonstrate that MGEMTIP can more accurately predict the DC resistivity and the chargeability of heterogeneous media. MGEMTIP is suitable for characterizing the polarization phenomena of rock with high salinity, low porosity, low hydraulic permeability, and a disseminated perturbed medium. Furthermore, the testing of rock samples for the inversion of IP parameters with MGEMTIP revealed that the predicted chargeability is higher than the inverted chargeability from the experimental data. This difference is strongly correlated with rock hydraulic permeability. MGEMTIP provides a petrophysical basis for the forward modeling and inversion of IP parameters of compacted rocks. The quantitative relationships between model IP parameters and reservoir parameters also provide a theoretical foundation for predicting reservoir permeability using electromagnetic methods.

Spectral induced polarization of clay-sand mixtures: Experiments and modeling

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. E353-E375 ◽  
Author(s):  
Gonca Okay ◽  
Phillipe Leroy ◽  
Ahmad Ghorbani ◽  
Phillipe Cosenza ◽  
Christian Camerlynck ◽  
...  
Keyword(s):  
Water Saturation ◽  
Effective Medium Theory ◽  
Induced Polarization ◽  
Complex Conductivity ◽  
Strong Impact ◽  
Conduction Model ◽  
Polarization Model ◽  
Sand Mixture ◽  
Conductivity Model ◽  
Spectral Induced Polarization

Spectral induced polarization or complex conductivity is a promising electric method in hydrogeophysics because of its sensitivity to water saturation, permeability, and particle size distribution (PSD). However, the physical and chemical mechanisms that generate the low-frequency complex conductivity of clays are still debated. To explain these mechanisms, the complex conductivity of kaolinite, smectite, and clay-sand mixtures was measured in the frequency range 1.4 mHz–12 kHz with various clay contents (100%, 20%, 5%, and 1% in volume of the clay-sand mixture) and salinities (distilled water, [Formula: see text], [Formula: see text], and [Formula: see text] of NaCl in solution). The results indicated the strong impact of the cation exchange capacity of smectite upon the complex conductivity of the material. The quadrature conductivity increased steadily with the clay content and was fairly independent of the pore fluid salinity. A mechanistic induced polarization model was also developed. It combined a Donnan equilibrium model of the surface electrochemical properties of clays and sand, a conduction model of the Stern and diffuse layers, a polarization model of the Stern layer, and a macroscopic conductivity model based on the differential effective medium theory. It also included the effect of the PSD. Our complex conductivity model predicted very well the experimental data, except for very low frequencies ([Formula: see text]) at which membrane polarization may dominate the observed response.

Anisotropy of induced polarization in the context of the generalized effective‐medium theory

2008 ◽  
Author(s):  
Michael S. Zhdanov ◽  
Alexander Gribenko ◽  
Vladimir Burtman ◽  
Vladimir I. Dmitriev
Keyword(s):  
Effective Medium Theory ◽  
Induced Polarization ◽  
Effective Medium ◽  
Medium Theory
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