Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Interpreting 3-D seismic data

  | chapter = Interpreting 3-D seismic data

  | frompg  = 13-1

  | frompg  = 13-7

  | topg    = 13-27

  | topg    = 13-9

  | author  = Geoffrey A. Dorn

  | author  = Geoffrey A. Dorn

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch13/ch13.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch13/ch13.htm

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Three-dimensional [[seismic interpretation]] is not just dense 2-D seismic interpretation. Although it is certainly possible to interpret the 3-D seismic volume as a dense 2-D grid (in fact, some early interactive interpretation systems actually encouraged this), this is neither an effective nor an efficient approach to the interpretation. The results are generally of poorer quality and require significantly more effort than interpreting the data in a 3-D fashion.

Three-dimensional [[seismic interpretation]] is not just dense 2-D seismic interpretation. Although it is certainly possible to interpret the 3-D seismic volume as a dense 2-D grid (in fact, some early interactive interpretation systems actually encouraged this), this is neither an effective nor an efficient approach to the interpretation. The results are generally of poorer quality and require significantly more effort than interpreting the data in a 3-D fashion.

==The 2-D approach==

==The 2-D approach==

==Example of seeing faults==

==Example of seeing faults==

[[file:interpreting-3-d-seismic-data_fig13-2.png|left|thumb|{{figure number|1}}From Dorn.<ref name=Dorn_1998>Dorn, G. A., 1988, [http://library.seg.org/doi/abs/10.1190/1.1438121 Modern 3-D seismic interpretation]: The Leading Edge, v. 17, no. 9, p. 1262-1271.</ref> Courtesy SEG.]]

[[file:interpreting-3-d-seismic-data_fig13-2.png|300px|thumb|{{figure number|1}}Images from a 3-D survey in the Gulf of Mexico. From Dorn.<ref name=Dorn_1998>Dorn, G. A., 1988, [http://library.seg.org/doi/abs/10.1190/1.1438121 Modern 3-D seismic interpretation]: The Leading Edge, v. 17, no. 9, p. 1262-1271.</ref> Courtesy SEG.]]

[[:file:interpreting-3-d-seismic-data_fig13-2.png|Figure 1]] shows several images from a 3-D survey in the Gulf of Mexico. Figure 2a is a dip magnitude map at an interpreted horizon in the data, showing several steep dip (pink) lineaments associated with normal faults that cut the horizon. Arrows ''b'', ''c'', and ''d'' show the orientation and direction of three traverses cut through the volume at angles of approximately 90°, 45°, and 10° to the trace of the fault in the center of the horizon. Figures 2b, c, and d are traverses ''b, c'', and ''d'', respectively. The fault is clearly interpretable in the centers of the traverses that cut the fault at angles of 90° and 45°. However, it would be very difficult to interpret the fault on Figure 2d, the oblique traverse. This geometric effect produces a blind zone on vertical sections that are oriented between +/–20° of the trend of a fault. As a result, if you are only interpreting vertical seismic sections, you will fail to see faults that have trends in this zone. The same phenomenon occurs with depositional stratigraphy.

[[:file:interpreting-3-d-seismic-data_fig13-2.png|Figure 1]] shows several images from a 3-D survey in the [[Gulf of Mexico]]. [[:file:interpreting-3-d-seismic-data_fig13-2.png|Figure 1a]] is a [[dip]] magnitude map at an interpreted horizon in the data, showing several steep dip (pink) lineaments associated with normal faults that cut the horizon. Arrows ''b'', ''c'', and ''d'' show the orientation and direction of three traverses cut through the volume at angles of approximately 90°, 45°, and 10° to the trace of the fault in the center of the horizon. [[:file:interpreting-3-d-seismic-data_fig13-2.png|Figure 1b, c, and d]] are traverses ''b, c'', and ''d'', respectively. The fault is clearly interpretable in the centers of the traverses that cut the fault at angles of 90° and 45°. However, it would be very difficult to interpret the fault on [[:file:interpreting-3-d-seismic-data_fig13-2.png|Figure 1d]], the oblique traverse. This geometric effect produces a blind zone on vertical sections that are oriented between +/–20° of the trend of a fault. As a result, if you are only interpreting vertical seismic sections, you will fail to see faults that have trends in this zone. The same phenomenon occurs with depositional stratigraphy.

The best section to image a channel is a section oriented at 90° to the trend of the channel.

The best section to image a channel is a section oriented at 90° to the trend of the channel.

==Start with time slices==

==Start with time slices==

The first step toward 3-D interpretation of a 3-D volume is to use time slices. The value of time-slice interpretation for faults is fairly obvious. Regardless of the strike of the fault, most fault surfaces intersect the time slice at an angle between 45° and 90° to the plane of the time slice

The first step toward 3-D interpretation of a 3-D volume is to use time slices. The value of time-slice interpretation for faults is fairly obvious. Regardless of the strike of the fault, most fault surfaces intersect the time slice at an angle between 45° and 90° to the plane of the time slice

==Computer limitations==

==Computer limitations==

 

[[file:interpreting-3-d-seismic-data_fig13-4.png|left|thumb|{{figure number|3}}From Dorn.<ref name=Dorn_1998 /> Courtesy SEG.]]

interpreting-3-d-seismic-data_fig13-3.png|{{figure number|2}}Time slice from a 3-D survey in the North Sea. From Dorn.<ref name=Dorn_1998 /> Courtesy SEG.

interpreting-3-d-seismic-data_fig13-4.png|{{figure number|3}}Traverse cut through the data in a direction perpendicular to the channel system. From Dorn.<ref name=Dorn_1998 /> Courtesy SEG.

Depositional systems are typically more interpretable on time slices than they are on vertical sections. [[:file:interpreting-3-d-seismic-data_fig13-3.png|Figure 2]] is a time slice from a 3-D survey in the North Sea. Aportion of a braided stream system is clearly evident.

Depositional systems are typically more interpretable on time slices than they are on vertical sections. [[:file:interpreting-3-d-seismic-data_fig13-3.png|Figure 2]] is a time slice from a 3-D survey in the North Sea. Aportion of a braided stream system is clearly evident.

[[:file:interpreting-3-d-seismic-data_fig13-4.png|Figure 3]] is a traverse cut through the data in a direction perpendicular to the channel system. Horizontal arrows indicate when the channel system occurs, and vertical arrows show the location of each of a number of individual channels cut by the traverse. It is safe to say that most if not all of these channels would have been missed if the interpretation had been limited to vertical sections.

[[:file:interpreting-3-d-seismic-data_fig13-4.png|Figure 3]] is a traverse cut through the data in a direction perpendicular to the channel system. Horizontal arrows indicate when the channel system occurs, and vertical arrows show the location of each of a number of individual channels cut by the traverse. It is safe to say that most if not all of these channels would have been missed if the interpretation had been limited to vertical sections.

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==See also==

==See also==

* [[Data preview]]

* [[Data preview]]

* [[Picking horizons in 3-D data]]

* [[Picking horizons in 3-D data]]

* [[Surface slicing]]

* [[Surface slicing]]

==References==

==References==

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

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

[[Category:Interpreting 3-D seismic data]]

[[Category:Interpreting 3-D seismic data]]