Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Interpreting seismic data

  | chapter = Interpreting seismic data

  | frompg  = 12-1

  | frompg  = 12-6

  | topg    = 12-29

  | topg    = 12-7

  | author  = Christopher L. Liner

  | author  = Christopher L. Liner

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch12/ch12.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch12/ch12.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

From the broad field of seismology, a few things seem to pop up with regularity. Some of these have been collected here. Keep them in mind when working with seismic data—in particular, 3-D seismic data.

From the broad field of seismology, a few things seem to pop up with regularity. Some of these have been collected here. Keep them in mind when working with [[seismic data]]—in particular, 3-D seismic data.

==The onion==

==The onion==

[[file:interpreting-seismic-data_fig12-1.png|thumb|{{figure number|1}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[file:interpreting-seismic-data_fig12-1.png|thumb|300px|{{figure number|1}}Seismic data is built of several layers like an onion. Copyright: Liner;<ref name=Liner>Liner, C., 1999, Elements of 3-D Seismology: Tulsa, PennWell.</ref> courtesy PennWell.]]

The knowledge required for working with seismic data is built of several layers like an onion. [[:file:interpreting-seismic-data_fig12-1.png|Figure 1]] illustrates the idea. At the heart of the onion are 1-D seismic concepts like [[wavelet]], [[convolution]], [[traveltime]], and [[reflection coefficient]]. All this shows up in the next layer, 2-D seismic, plus [[Seismic array|arrays]], [[offset]], [[dip]], and [[lateral velocity]] variation. The next layer, 3-D seismic, includes all of 2-D plus [[azimuth]], [[Components of a 3-D seismic survey#Bins|bins]], and the [[3-D seismic: the data cube|data volume]]. Finally, 4-D seismic is time-lapse 3-D, which introduces [[repeatability]], [[Fundamentals of fluid flow|fluid flow]], and [[difference volume]].

The knowledge required for working with seismic data is built of several layers like an onion. [[:file:interpreting-seismic-data_fig12-1.png|Figure 1]] illustrates the idea. At the heart of the onion are 1-D seismic concepts like [[wavelet]], [[convolution]], [[traveltime]], and [[reflection coefficient]]. All this shows up in the next layer, 2-D seismic, plus [[Seismic array|arrays]], [[offset]], [[dip]], and [[lateral velocity]] variation. The next layer, 3-D seismic, includes all of 2-D plus [[azimuth]], [[Components of a 3-D seismic survey#Bins|bins]], and the [[3-D seismic: the data cube|data volume]]. Finally, 4-D seismic is time-lapse 3-D, which introduces [[repeatability]], [[Fundamentals of fluid flow|fluid flow]], and [[difference volume]].

* [[Rock properties|Rock]] and [[Petroleum reservoir fluid properties|fluid properties]]

* [[Rock properties|Rock]] and [[Petroleum reservoir fluid properties|fluid properties]]

In this order, each task requires increasing data quality. Quality is a nebulous term largely determined during acquisition  by correct [[Seismic survey design\survey design]] and execution.  (For more information about acquisition, please see [[Seismic data acquisition on land]] and [[Marine seismic data acquisition]].)  [[Basic seismic processing|Processing]] generally has less impact on quality but is still very important.

In this order, each task requires increasing data quality. Quality is a nebulous term largely determined during acquisition  by correct [[Seismic survey design|survey design]] and execution.  (For more information about acquisition, please see [[Seismic data acquisition on land]] and [[Marine seismic data acquisition]].)  [[Basic seismic processing|Processing]] generally has less impact on quality but is still very important.

==Echo location==

==Echo location==

==Traveltimes and amplitudes==

==Traveltimes and amplitudes==

In one sense, seismic data consist of traveltime, amplitude, and waveform information. Structure mapping involves only the traveltimes, stratigraphy involves both traveltime and amplitude, and rock/fluid property information lives in the amplitude and waveform.

In one sense, seismic data consist of [[traveltime]], [[amplitude]], and [[waveform]] information. [[Structure]] mapping involves only the traveltimes, [[stratigraphy]] involves both traveltime and amplitude, and [[Rock properties|Rock]] and [[Petroleum reservoir fluid properties|fluid property]] information lies in the amplitude and waveform.

==Edges==

==Edges==

[[file:interpreting-seismic-data_fig12-2.png|thumb|{{figure number|2}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[file:interpreting-seismic-data_fig12-2.png|300px|thumb|{{figure number|2}}. Copyright: Liner;<ref name=Liner /> courtesy PennWell.]]

If you look at a rock outcrop, you see sandstone, shale, limestone, etc. If you look at seismic data, you see the edges of rock units. The figure below shows the edge effect on a Gulf of Mexico salt dome example. Seismic is, in effect, an edge detection technique. The bigger the velocity and/or density contrast between the rocks, the stronger the edge.

If you look at a [http://www.merriam-webster.com/dictionary/outcrop rock outcrop], you see [[sandstone]], [[shale]], [[limestone]], etc. If you look at seismic data, you see the edges of rock units. The figure below shows the edge effect on a [[Gulf of Mexico]] [[salt dome]] example. Seismic analysis is, in effect, an edge detection technique. The bigger the [[velocity]] and/or [[density]] contrast between the rocks, the stronger the edge.

To be fair, seismic impulses respond to much more than just lithology. Any vertical variation in rock property that modifies the velocity or density can potentially generate seismic reflections, including a fluid contact, [[porosity]] variation, or shale density change.

To be fair, seismic impulses respond to much more than just lithology. Any vertical variation in rock property that modifies the velocity or density can potentially generate [[seismic reflection]]s, including a [[Fluid contacts|fluid contact]], [[porosity]] variation, or shale density change.

==Event tracking==

==Event tracking==

A key part of the interpretation process for 3-D seismic data is event tracking. To picture this, think of the 3-D seismic data volume as a block of vanilla ice cream with chocolate streaks. Tracking means we follow a streak into the cube and find out where it goes—this is structure mapping. We also keep track of how dark the chocolate is as we follow it—this is amplitude mapping.

A key part of the interpretation process for 3-D [[seismic data]] is event tracking. To picture this, think of the [[3-D seismic: the data cube|3-D seismic data volume]] as a block of vanilla ice cream with chocolate streaks. Tracking means we follow a streak into the cube and find out where it goes—this is [[Seismic structure map|structure mapping]]. We also keep track of how dark the chocolate is as we follow it—this is [[amplitude map]]ping.

==Computer limitations==

==Computer limitations==

Available computer speed and memory impose severe limitations on the use of advanced 3-D seismic processing. Current hardware is sufficient for the interpretation process, but the software can be complicated and expensive ([[cost::5,000 USD]]-[[cost::180,000 USD]]).

Available computer speed and memory impose severe limitations on the use of advanced 3-D seismic processing. Current hardware is sufficient for the interpretation process, but the software can be complicated and expensive.

==See also==

==See also==

* [[Components of a 3-D seismic survey]]

* [[Components of a 3-D seismic survey]]

* [[3-D seismic data views]]

* [[3-D seismic data views]]

==External links==

==External links==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Interpreting seismic data]]

[[Category:Interpreting seismic data]]