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At present the most established and formalized is the method of linear EM soundings (tCSEM) and reconstruction of the medium parameters on basis of 1D, as a rule, horizontally layered model. However, this approach often results in considerable mistakes in a real 3D medium. The technology based on multispaced area systems of observation, with the fixed transmitter of the electromagnetic (EM) field, and the 3D inversion is discussed in this paper. New possibilities provided by the tech-nology of nonstationary electrical survey, as an independent method of solving search problems are shown here, the reconstruction of a compound geological structure of one of the ore-fields being taken as an example. The developed technology can also be successfully used for the reconstruction of hydrocarbon reservoirs structure.
The paper considers:
Errors of 1D parameterization of electromagnetic survey data. For this purpose two conducting objects are placed in a two-layered medium consisting of a low-conducting upper layer and a relatively conducting foundation. One of these objects is near-surface and is placed directly beneath the profile and the second object is a subvertical conducting body and is placed at one side of the profile. 1D inversion significantly distorts the shape of the conduc-tive foundation which is falsely presented as a considerable rise. Side effects produced by the objects in the upper part of the section are taken into account by making additional measurements along orthogonal cross-sections. Cross-sections location is defined by arias of maximum discrep-ancy of inverse problem solution in terms of 1D mathematical model. The example of area soundings reconstruction into the volume medium conductivitiy distribution when performing structural geomapping of the Karamken ore-field. Volume reconstruction of a gold-ore field has been obtained on the basis of electromagnetic soundings for the first time. Fundamental structural elements of a compound geological medium have been specified. A subvertical object unknown before has been discovered, this object is identified as an ore-supplying channel. The effectiveness of carrying out the investigations with a fix inductive field source when per-forming depth soundings, including those performed in highlands, is shown.
The possibility of usage of the developed technology when reconstructing hydrocarbon res-ervoirs. A typical model of a terrigenous reservoir with considerably heterogeneous upper part of a section is considered. The space-time field distribution in these conditions and the time range of the traps display are shown. It was determined that the induction loop is the most effective source to carry out the investigations when solving this type of problems. The possibility of determining a fluid-saturated collector type using area and profile-area observation systems, taking into account the volume model of geological medium, is shown.
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