Geophysical research: article

Аnnotation: When interpreting the data of the electrical prospecting method of sounding by transient electromagnetic method in the near zone (TEM), there is a large uncertainty caused by the choice of the optimal approach to inversion. The one-dimensional approach was considered classical, however, with the development of the method (in particular, the mathematical apparatus and computing power), a three-dimensional approach was formed, which is based on the idea that the probed space is mostly horizontally inhomogeneous and the use of the one-dimensional approach introduces critical inaccuracies in data interpretation. An important part of this article is examples of empirical assessment of the effectiveness of applying one-dimensional and three-dimensional approaches to inversion of TEM data in relation to geological conditions, typical of the south Siberian craton, when solving oil and gas prospecting problems. It was established that, despite the versatility of three-dimensional modeling, the choice of an approach to inversion should be carried out individually in each case, based on the dimension of the studied environment. To determine the boundary levels of the dimension of the medium, which corresponds to the TEM data, a mathematical experiment was carried out, during which the criteria for applying the three-dimensional approach to data inversion were established. The mentioned criteria are the root-mean-square divergence of the apparent resistivity curves obtained within one sounding installation, more than 10% and the discrepancy of one-dimensional inversion of more than 10 %, which minimization is impossible in the space of models determined by a priori data. In other cases, the geological problems facing the TEM method are successfully solved using a one-dimensional approach. On the basis of the above criteria, an analysis of the dimension of 90 thousand physical observations obtained in the south of the Siberian craton was carried out, during which it was established that in relation to the TEM, the one-dimensional approach can be considered as the basic one.