Saeed Nazari; Alireza Arab Amiri; Abolghasem Kamkar Rouhani; Fereydoun Sharifi
Abstract
In this work, we simulate the frequency-domain helicopter-borne electromagnetic (HEM) data over the two-dimensional (2D) and three-dimensional (3D) earth models. In order to achieve this aim, the vector Helmholtz equation is used to avoid the convergence problems in Maxwell’s equations, and the ...
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In this work, we simulate the frequency-domain helicopter-borne electromagnetic (HEM) data over the two-dimensional (2D) and three-dimensional (3D) earth models. In order to achieve this aim, the vector Helmholtz equation is used to avoid the convergence problems in Maxwell’s equations, and the corresponding fields are divided into primary and secondary components. We use the finite difference method on a staggered grid to discretize the equations, which can be performed in two ways including the conventional and improved finite difference methods. The former is very complex in terms of programming, which causes errors. Furthermore, it requires different programming loops over each point of the grid, which increases the program’s running time. The latter is the improved finite difference method (IFDM), in which pre-made derivative matrices can be used. These pre-made derivative matrices can be incorporated into the derivative equations and convert them directly from the derivative form to the matrix form. After having the matrix form system of linear equations, Ax = b is solved by the quasi-minimal residual (QMR). IFDM does not have the complexities of the conventional method, and requires much less execution time to form a stiffness or coefficient matrix. Moreover, its programing process is simple. Our code uses parallel computing, which gives us the ability to calculate the fields for all transmitter positions at the same time, and because we use sparse matrices thorough the code memory space, requires to store the files is less than 100 MB compared with normal matrices that require more than 15 GB space in the same grid size. We implement IFDM to simulate the earth’s responses. In order to validate, we compare our results with various models including the 3D and 2D models, and anisotropic conductivity. The results show a good fit in comparison with the FDM solution of Newman and the appropriate fit integral equations solution of Avdeev that is because of the different solution methods.
F. Sharifi; A.R. Arab Amiri; A. Kamkar Rouhani
Abstract
The generalized effective-medium theory of induced polarization (GEMTIP) is a newly developed relaxation model that incorporates the petro-physical and structural characteristics of polarizable rocks in the grain/porous scale to model their complex resistivity/conductivity spectra. The inversion of the ...
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The generalized effective-medium theory of induced polarization (GEMTIP) is a newly developed relaxation model that incorporates the petro-physical and structural characteristics of polarizable rocks in the grain/porous scale to model their complex resistivity/conductivity spectra. The inversion of the GEMTIP relaxation model parameter from spectral-induced polarization data is a challenging issue because of the highly non-linear dependency of the observed data on the model parameter and non-uniqueness of the problem. To solve these problems as well as scape the local minima of the highly complicated cost function, the genetic algorithm (GA) can be applied but it has proven to be time-intensive computationally. However, this drawback can be resolved by incorporating a faster algorithm, e.g. particle swarm optimization (PSO). The aim of this work is to investigate whether recovering the model parameter of the ellipsoidal GEMTIP model from SIP data using the combined GA and PSO algorithms is possible. To achieve this aim, we set the best calculated individuals using GA as the search space of PSO, and then the best location achieved by PSO in each iteration is assigned as the updated model parameters. The results of our research work reveal that the model parameters can effectively be recovered using the approach proposed in this paper but the time constant of a noisy data that arises from the adverse dependency of this parameter on the ellipticity of a polarizable grain. Moreover, the execution time of the ellipsoidal GEMTIP modeling of complex resistivity data can be significantly improved using the proposed algorithm.
Alireza Arab-Amiri; Fereydoun Sharifi; Abolghasem Kamkar-Rouhani
Abstract
The need for clean groundwater resources to have sustainable development in a country is undoubted. Due to the importance and high quality of karstic waters in supplying water in Iran especially in Shahrood city, it is attempted in this research work to recognize and explore karstic waters in southwest ...
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The need for clean groundwater resources to have sustainable development in a country is undoubted. Due to the importance and high quality of karstic waters in supplying water in Iran especially in Shahrood city, it is attempted in this research work to recognize and explore karstic waters in southwest of Tepal area, Shahrood. For this purpose, integration of the results obtained from the methods of vertical electrical sounding (VES) and resistivity profiling has been used in this research work. The VES surveys have been performed in 10 sounding points using the Schlumberger array with electrode separations of a maximum 500 meters. The resistivity profiling surveys using dipole-dipole electrode array with 75m electrode spacing and dipole steps 1 to 8 have been carried out along four lines having a length of more than four kilometers in the study area. Then, one-dimensional (1-D) modeling and interpretation of the sounding results using master curves and IX1D software, and two-dimensional (2-D) modeling and interpretation of the profiling results using Res2DINV have been made. As a result of the interpretation and integration of the results, karstic water zones in the study area have been recognized, and based on that, suitable locations for drilling to access and extract karstic groundwater have been introduced.
