Glossary
Image polarity
End member colour assignment of borehole image or dipmeter data based on the range of resistivity or sonic response. In the standard convention conductive or acoustically absorbent lithologies map to dark colours whereas resistive or acoustically reflective rocks map to brighter colours. Image polarity can be checked by comparison with resistivity or acoustic log or against a known reference lithology such as a resistive carbonate body.
During interpretation of borehole images, the eye is drawn to darker colours, leading to a visual bias in the analysis of a given section. To offset this bias it is often sufficient to reverse the polarity of the images interactively, remembering to change back so as to keep a standard scheme.
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About the glossary
This listing is not exhaustive or definitive, do not expect Oxford English Dictionary standards; it is aimed at those who need to understand basic principles and those that read reports on dipmeters and borehole images requiring some technical help to get the most from such documents.
We have attempted to make the descriptions and explanations generic, giving the glossary a wide application and appeal, with minimal, if any, commercial bias. If you spot any mistakes, omissions or any problems with the explanations, please do not hesitate to contact us, and we will try to accommodate your comments.
Acknowledgements
This listing has been derived by Task Geoscientists. All external sources are fully acknowledged.