engleski

Determination of resolution limits of electrical tomography on the block model in a homogenous environment by means of electrical modelling

The block model in a homogenous environment can generally serve for presentation of some geological models: changes of facies, changes of rock compactness-fragmentation, underground cavities, bauxite deposits, etc. Therefore, on the block model of increased resistivities in a homogenous environment of low resistivity, the potentials of the electrical tomography methods were tested for the purpose of their detection. In order to analyze the resolution of the method, both interpretation methods were used: electrical forward modelling and electrical inversion. Forward modelling enabled the calculation of theoretical, measured pseudosection for any given model, while inversion was used for the analysis of resolution and potentials of specific block recognition for a specific model. Regarding potentials of block detection, resolution methods depend on: depth of block location, ratio between block resistivity and the environment in which it is located as well as applied survey geometry, i.e. electrode array. Thus the analyses carried out for the most frequently used electrode arrays in the investigations are the following: the Wenner, Wenner-Schlumberger, dipole-dipole and pole-pole arrays. For each array, maximum depths at which a block can be detected relative to the ratio between block resistivity and parent rock environment were analyzed. As a representative, the block of dimensions 40x20 m was selected, located in the homogenous environment of low resistivity (100 ohmm). Its resistivity is set in ratios towards the environment in the range from 1.25 to 2500. The results are shown in the two-dimensional graphs, where the ratio between the block resistivity and the environment is shown on the X-axis, and the resolution depth on the Y-axis, after which the curves defining the resolution limits were drawn. These graphs have a practical use, since they enable a fast, simple determination of potentials of the method application on a specific geological model. Regarding their shape, resolution curves are similar for all arrays, where resolution depth generally increases with increased resistivity ratio until a certain maximum depth is reached. The lowest resolution is enabled by the Wenner, and the highest by the dipole-dipole array. The Wenner array enables the maximum resolution depth of 80 m, which is achieved for the resistivity ratio of 30, whereas the dipole-dipole array enables the detection at depths to 140 m for resistivity ratios above 30.

electrical tomography; resolution; electrical modelling; geological models

nije evidentirano