Анализ эквивалентности трехмерных моделей при 3D-интерпретации данных аэроэлектроразведки

Abstract

The article is devoted to the problem of the equivalence of three-dimensional geoelectric models obtained as a result of 3D-interpretation of aerial electrical survey data in medium where local conductive bodies are covered by a heterogeneous near-surface layer. To carry out the research, we used data from aerial electrical prospecting carried out in the Creighton area (Canada) when searching for polymetallic ores. A two-stage 3D-inversion was used to build the geoelectric model. The purpose of the first stage of 3D-inversion was to reconstruct near-surface structures based on survey data obtained at the early times. The second stage of 3D-inversion was based on the residual map constructed from the practical signals and the signals obtained after the first stage of 3D-inversion at later times. Using the residual map, the starting positions of local bodies under the overlying layer were specified, and their geometry and properties were obtained during local 3D-inversions. Based on the results of 3D-inversion, a local conductive body was identified and confirmed by drilling data. An equivalence analysis was carried out for a three-dimensional model of this body. Various options for initial models differing in the number of blocks describing the body were considered, as well as options for changing the size of blocks in the model obtained as a result of 3D-inversion. It was found that the main equivalence is related to the large distance between flight lines, which is several times greater than the distance between positions on the profile. Therefore, most equivalent models are characterized by a decrease in the size of blocks in the direction orthogonal to the profiles, due to an increase in their size along the profile and a change in resistivity. At the same time, according to the criterion for drilling wells, the resulting equivalent models were identical, i.e. from a geological point of view, no fundamental difference was found between the resulting equivalent models.