On the electric fields and currents produced by induction logging instruments in anisotropic media
| Autor: | Chester J. Weiss, Xinyou Lu, David Alumbaugh |
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| Rok vydání: | 2002 |
| Předmět: | |
| Zdroj: | GEOPHYSICS. 67:478-483 |
| ISSN: | 1942-2156 0016-8033 |
| DOI: | 10.1190/1.1468607 |
| Popis: | Electrical anisotropy has attracted the interest of the induction logging community for several decades now in their efforts to better characterize potential hydrocarbon reservoirs (e.g., Kunz and Moran, 1958; Moran and Gianzero, 1979; Anderson et al., 1998). Shale formations and thinly laminated sequences of shale and sand are commonly-encountered anisotropic formations (Klein et al., 1995). These types of formations are likely to exhibit one (value of conductivity parallel to the bedding planes, and a different, lesser, value of conductivity perpendicular to beds. This is the case of transverse isotropy . Historically, exploration wells were drilled vertically, and thus were often perpendicular to formation bedding planes. In this situation, conventional coaxial induction tools induce eddy currents that flow horizontally (i.e., parallel to the bedding planes). Thus conventional induction tools are only sensitive to the horizontal formation conductivity. This is the primary reason why electrical anisotropy has been largely ignored by many log analysts until recently. However, deviated and horizontal wells have been increasingly used as a new drilling strategy to better characterize the reservoir and lower exploitation costs. The induced currents produced by a sonde located within a deviated or horizontal well are forced to cross bed boundaries, and thus are sensitive to both the vertical and horizontal conductivity of the formation. An arbitrarily oriented magnetic dipole source can be represented as the superposition of one vertical and two horizontal magnetic dipole sources. Whereas transverse anisotropy has no effect on the fields induced by a vertical magnetic dipole, the effects of anisotropy on the two horizontal dipoles are significant. Therefore, a horizontal magnetic dipole exciting a transversely isotropic whole space is a reasonable starting point in understanding induction logging in anisotropic media. The induction problem for a horizontal magnetic dipole source in the presence of anisotropic whole space or … |
| Databáze: | OpenAIRE |
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