SIGNALS OF RESISTIVITY LOGGING TOOL WITH TOROIDAL COILS PHYSICAL AND MATHEMATICAL MODELING
I.V. Mikhaylov1,2, I.S. Oshlykov3, I.V. Surodina1,4, M.N. Nikitenko1, V.N. Glinskikh1,2
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Novosibirsk State Technical University, Novosibirsk, Russia
4Institute of Computational Mathematics and Mathematical Geophysics SB RAS,Novosibirsk, Russia
Keywords: electromagnetic logging, toroidal coils, physical modeling, mathematical modeling, finite-difference method, geoelectric model, profiling, signal transformation
Abstract
The study compares in detail the signals of an electromagnetic tool with toroidal coils, which were measured in an electrolytic tank with a borehole and numerically calculated in its three-dimensional geoelectric model. For each specific electrical resistivity of the electrolyte, we performed the profiling of the “air-tank” and “tank-borehole” boundaries during the round-trips of the tool. Values of the coupling coefficient of the measured and modeled signals were determined for the entire set of frequencies and positions of the measuring coils in the summary and differential operating modes. We identified a pair of the signals with a virtually constant coupling coefficient at varying electrolyte mineralization. Drawing on this pair, transformations of the tool signals into the apparent electrical resistivities of the medium were constructed. The resulting transformation graphs allow a reliable recalculation of the measured signals of the toroidal tool into the apparent electrical resistivity distribution in the near-wellbore space, which is necessary for the petrophysical interpretation of the field-log data.
|
