A modelling of effects of variable saturation in invaded zone near borehole on neutron tool response in the gas-bearing Miocene formations of the Carpathian foredeep,Poland |
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Authors: | M Ba?a U Wo?nicka T Zorski A Drabina |
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Institution: | 1. Department of Applied Geophysics, Technische Universität Berlin, Ernst-Reuter-Platz 1, BH 1-1, Berlin 10587, Germany;2. Institute of Geophysics and Geoinformatics, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Straße 12, Freiberg 09596, Germany |
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Abstract: | Invasion of mud filtrate from the borehole into the surrounding formation can significantly alter the response of logging tools.In this paper the neutron tool response was calculated for a gas-bearing rock crossed by the borehole.The invaded zone is characterized by variable fluid and gas saturation and is defined by a specific hyperbolic function. The saturation function is based on the characteristics of Polish Carpathian Foredeep Miocene formations reached in gas-bearing rocks. The whole system including neutron tool equipped with Am-Be neutron source and a set of neutron detectors, borehole, invaded zone, and virgin zone, was numerically modeled and used as the input to the Monte-Carlo neutron transport code. The response of each detector was calculated for different combinations of porosity and saturation of invaded zone and virgin zone. |
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