In reflection seismology, a polarity reversal or phase change is a local amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator. It primarily results from the change in polarity of the seismic response when a shale (with a lower acoustic impedance) overlies a brine-saturated zone (with a high acoustic impedance), that becomes invaded with an oil/gas sand (with the lowest acoustic impedance of the three). This changes the acoustic impedance contrast from an increase to a decrease, resulting in the polarity of the seismic response being reversed - as per the normal convention adopted by the SEG.
Diagram showing the acoustic relationship that results in a seismic polarity reversal.
Occurrenceedit
For a polarity reversal to occur, the shale has to have a lower acoustic impedance than the water sand and both are required to have a higher acoustic impedance than the oil/gas sand. This is the intermediate situation, that occurs during sediment compaction with depth, between the acoustic impedance relationship required for a bright spot and the acoustic impedance relationship required for a dim spot.
Referencesedit
"dim spot". Oilfield Glossary. Schlumberger. Retrieved 10 April 2013.
Brown, Alistar (February 2010). "Good News: A Dim Future Isn't Bad!". AAPG Explorer.
Hilterman, Fred J. (2001). Seismic amplitude interpretation: 2001 distinguished instructor short course. Houston, TX: SEG. ISBN9781560801092.
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polarity, reversal, seismology, reflection, seismology, polarity, reversal, phase, change, local, amplitude, seismic, attribute, anomaly, that, indicate, presence, hydrocarbons, therefore, known, direct, hydrocarbon, indicator, primarily, results, from, change. In reflection seismology a polarity reversal or phase change is a local amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator It primarily results from the change in polarity of the seismic response when a shale with a lower acoustic impedance overlies a brine saturated zone with a high acoustic impedance that becomes invaded with an oil gas sand with the lowest acoustic impedance of the three This changes the acoustic impedance contrast from an increase to a decrease resulting in the polarity of the seismic response being reversed as per the normal convention adopted by the SEG Diagram showing the acoustic relationship that results in a seismic polarity reversal Occurrence editFor a polarity reversal to occur the shale has to have a lower acoustic impedance than the water sand and both are required to have a higher acoustic impedance than the oil gas sand This is the intermediate situation that occurs during sediment compaction with depth between the acoustic impedance relationship required for a bright spot and the acoustic impedance relationship required for a dim spot References edit dim spot Oilfield Glossary Schlumberger Retrieved 10 April 2013 Brown Alistar February 2010 Good News A Dim Future Isn t Bad AAPG Explorer Hilterman Fred J 2001 Seismic amplitude interpretation 2001 distinguished instructor short course Houston TX SEG ISBN 9781560801092 nbsp This seismology article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Polarity reversal seismology amp oldid 1192611356, wikipedia, wiki, book, books, library,
