Faculty of Mining, Geology and Petroleum Engineering University of Zagreb
Abstract
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 method were tested for the purpose of their detection. 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. 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.Model bloka u homogenoj sredini općenito može poslužiti za predočavanje nekih geoloških modela: promjena facijesa, promjena kompaktnosti-raspucanosti stijena, podzemnih šupljina, ležišta boksita i dr. Zato su na modelu bloka povišenih otpornosti u homogenoj sredini niskih otpornosti ispitane mogućnosti metode električne tomografije u njihovom otkrivanju. Mogućnost otkrivanja bloka, rezolucija metode ovisi o: dubini smještaja bloka, omjeru otpornosti bloka i sredine u kojoj se nalazi i primijenjenoj geometriji snimanja, to jest elektrodnom rasporedu. Zato su analize načinjene za najčešće korištene elektrodne rasporede u istraživanjima: Wennerov, Wenner-Schlumbergerov, dipolni i dvoelektrodni. Za svaki raspored analizirane su maksimalne dubine na kojima se može otkriti blok u ovisnosti o omjeru otpornosti bloka i matične sredine. Rezultati su prikazani na dvodimenzionalnim grafovima gdje se na apscisi nalazi omjer otpornosti bloka i sredine, a na ordinati maksimalna dubina razlučivosti, pa su izvučene krivulje koje definiraju granice razlučivosti. Ovi grafovi imaju praktičnu primjenu, jer omogućuju vrlo brzo i jednostavno određivanje mogućnosti primjene metode na određenom geološkom modelu
