Effects of borehole casing on TEM response |
| |
| Institution: | 1. A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Koptyuga 3, 630090, Novosibirsk, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. Geophysics, Department of Physics, University of Oulu, Finland;2. Department of Earth Sciences, Geophysics, Uppsala University, Uppsala, Sweden;3. Institute of Geophysics, ETH Zürich;1. Institut de Recerca, Centre Mixt d''Investigació GEOMODELS, Group of Geodynamics and Basin Analysis, Dept. Geodinàmica i Geofísica, Universitat de Barcelona (UB), Spain;2. Spanish Geological Survey (IGME), Rios Rosas 23, 28003 Madrid, Spain;1. Tomsk Polytechnic University, pr. Lenina 30, Tomsk, 634050, Russia;2. Chinggis Khaan Bank, 15 Chinggis Ave., Ulaanbaatar, Mongolia;1. College of Environmental Science and Engineering, State Environmental Protection Engineering Center for Pollution Treatment and Control in Textile Industry, Donghua University, Shanghai 201620, China;2. Nanjing Branch of Jiangsu Provincial Bureau of Hydrology and Water Resources Survey, Nanjing 210008, China;3. China Institute of Water Resource and Hydropower Research, Beijing 100038, China |
| |
| Abstract: | The effect the metal casing of a vertical borehole may exert on transient electromagnetic (TEM) responses has been studied in a field experiment. Eddy currents in the casing affect transients only slightly at early times, but the casing effect predominates at late times. Therefore, early-time TEM response measured near a borehole can provide information on shallow subsurface. The late-time TEM signals induced by the eddy currents in the casing show exponential behavior b? exp(–t/τ). The time constant τ refers to the rate of eddy current decay in the casing; the amplitude b is M12? M23? L–1? τ–1, where L is the casing self-inductance, and M12 and M23 are the mutual inductances between the transmitter loop and the borehole and between the borehole and the receiver, respectively. Both M12 and M23 are controllable, while M23 is especially important for survey applications: by reducing it, one can reduce the casing effect on the TEM data.© 2014, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
