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Magnetics: total intensity and residual magnetic maps (view source)
Revision as of 21:18, 17 January 2014
, 21:18, 17 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Using magnetics in petroleum exploration
| frompg = 14-1
| topg = 14-20
| author = Edward A. Beaumont, S. Parker Gay
| link = http://archives.datapages.com/data/specpubs/beaumont/ch14/ch14.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
Magnetic variation or susceptibility may be analyzed using either total intensity or residual maps. Magnetic residual maps reveal much more detailed geologic features—in particular, the geometry and configuration of individual basement blocks. They bring out the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries. Total intensity maps show larger scale geologic features, such as basin shape or anomalous rock types deep within the basement.
==What is total intensity?==
Total intensity is the measurement from the magnetometer after a model of the earth's normal magnetic field is removed. It is generally a reflection of the average magnetic susceptibility of broad, large-scale geologic features.
==What is residual?==
Residual is what remains after regional magnetic trends are removed from the total intensity Residual maps show local magnetic variations, which may have exploration significance. The regional trend of the total intensity can be calculated using a number of techniques, including running averages, polynomials, low-pass filters, or upward continuation techniques. The figure below shows magnetic profiles of total intensity, regional trend, and residual.
[[file:using-magnetics-in-petroleum-exploration_fig14-2.png|thumb|{{figure number|14-2}}After .<ref name=ch14r7>Nettleton, 1962, Elementary Gravity and [[Magnetics]] for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series 1, 121 p.</ref> Copyright: Society of Exploration Geophysicists.]]
==Total intensity and residual map example==
The maps below are examples of a residual map (A) that was calculated from the total intensity magnetic map (B). The grid and small circles on the total intensity map are the flight path lines [approximately [[length::2 km]] (1.2 mi) apart] and location points for the flight lines. The total intensity map strikingly does not resemble the residual map and would be of limited value for delineating basement fault blocks.
Total intensity [[magnetics]] responds to rock types over broad areas as well as those deep within the crust. We can see by a careful examination of map B, however, that many of the features shown by the residual map are vaguely apparent in the total intensity data. Fortunately, we no longer have to interpret such total intensity maps in petroleum basins because many enhancement techniques employing residuals, derivatives, polynomials, or downward continuation exist to reveal the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries.
[[file:using-magnetics-in-petroleum-exploration_fig14-3.png|thumb|{{figure number|14-3}}. Copyright: Gay, 1995; courtesy International Basement Tectonics Assoc.]]
==See also==
* [[Magnetic Basics]]
* [[Basics of magnetics]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch14/ch14.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Using magnetics in petroleum exploration]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Using magnetics in petroleum exploration
| frompg = 14-1
| topg = 14-20
| author = Edward A. Beaumont, S. Parker Gay
| link = http://archives.datapages.com/data/specpubs/beaumont/ch14/ch14.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
Magnetic variation or susceptibility may be analyzed using either total intensity or residual maps. Magnetic residual maps reveal much more detailed geologic features—in particular, the geometry and configuration of individual basement blocks. They bring out the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries. Total intensity maps show larger scale geologic features, such as basin shape or anomalous rock types deep within the basement.
==What is total intensity?==
Total intensity is the measurement from the magnetometer after a model of the earth's normal magnetic field is removed. It is generally a reflection of the average magnetic susceptibility of broad, large-scale geologic features.
==What is residual?==
Residual is what remains after regional magnetic trends are removed from the total intensity Residual maps show local magnetic variations, which may have exploration significance. The regional trend of the total intensity can be calculated using a number of techniques, including running averages, polynomials, low-pass filters, or upward continuation techniques. The figure below shows magnetic profiles of total intensity, regional trend, and residual.
[[file:using-magnetics-in-petroleum-exploration_fig14-2.png|thumb|{{figure number|14-2}}After .<ref name=ch14r7>Nettleton, 1962, Elementary Gravity and [[Magnetics]] for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series 1, 121 p.</ref> Copyright: Society of Exploration Geophysicists.]]
==Total intensity and residual map example==
The maps below are examples of a residual map (A) that was calculated from the total intensity magnetic map (B). The grid and small circles on the total intensity map are the flight path lines [approximately [[length::2 km]] (1.2 mi) apart] and location points for the flight lines. The total intensity map strikingly does not resemble the residual map and would be of limited value for delineating basement fault blocks.
Total intensity [[magnetics]] responds to rock types over broad areas as well as those deep within the crust. We can see by a careful examination of map B, however, that many of the features shown by the residual map are vaguely apparent in the total intensity data. Fortunately, we no longer have to interpret such total intensity maps in petroleum basins because many enhancement techniques employing residuals, derivatives, polynomials, or downward continuation exist to reveal the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries.
[[file:using-magnetics-in-petroleum-exploration_fig14-3.png|thumb|{{figure number|14-3}}. Copyright: Gay, 1995; courtesy International Basement Tectonics Assoc.]]
==See also==
* [[Magnetic Basics]]
* [[Basics of magnetics]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch14/ch14.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Using magnetics in petroleum exploration]]