Lecture of seismic

Department of Earth & Environmental Sciences,

Bahria University, Karachi Campus

www.bahria.edu.pk By: M. Hammad [email protected]

3D SEISMIC INTERPRETATION (GEO3D SEISMIC INTERPRETATION (GEO--518)518)

M. S (Geophysics)M. S (Geophysics)

By InstructorBy Instructor

M. Hammad ManzoorM. Hammad Manzoor

March 13, 2015 (Friday)March 13, 2015 (Friday) Lecture # 5Lecture # 5Lecture # 5Lecture # 5



KEY TO 3-D SEISMIC INTERPRETATION


(Important Terminologies)



3D DISPLAYS

• Unlike two-dimensional data, which are viewed only along shot lines,displays in a 3-D data volume may be extracted along any plane. Theseplanes are often vertical, although they need not be.

• The volume may also be sliced horizontally, and several vertical andhorizontal slices may be displayed simultaneously on the workstation

IMPORTANT TERMINOLOGIES


horizontal slices may be displayed simultaneously on the workstationscreen. Vertical sections are created by selecting adjacent seismic tracesfrom the data volume along a line in any orientation.

• The extracted seismic traces are then displayed side-by-side to form avertical seismic section display that looks like a traditional 2-D seismic line.These displays are used for convenience of display and picking, not becausethere are no other ways to view the seismic data.



3D DISPLAYS

• No single display orientation extracted from a 3-D data volume has morevalidity or is preferred over any other orientation. All are comprised oftraces from the same processed volume and, therefore, all of the sectionstie all other sections extracted from the 3-D data volume.





INLINE

• By convention, inline sections are vertical profiles along the generaldirection of data acquisition. They are sometimes thought of as thetraditional orientation of seismic sections for the survey, and lines areusually numbered from 1 to n.

CROSSLINE



CROSSLINE

• Crosslines are another way to sample and extract data from the 3-D volume,resulting in a vertical section display that is perpendicular to the directiondefined by the inlines. A crossline may be acquired in the field or createdfrom the 3-D data volume by taking traces from each of the inline sectionsand displaying them together to create a seismic section.



• For example, if trace number 100 were taken from each inline, together theywould form crossline 100. There may be as many different crosslines in asurvey as there are traces in each line. Crosslines are named and numberedfor convenience only





ARBITRARY LINE

• Another display unique to 3-D is a line extracted from the data volumewhich does not follow the orthogonal directions of inline and crossline, butcuts across the 3-D data volume in some arbitrary direction. Traces areextracted or interpolated from the 3-D data volume to make up the tracesof this "arbitrary line" which may, for example, be composed of linesegments joining several wells. Although made up of several line segments,



segments joining several wells. Although made up of several line segments,arbitrary lines are usually displayed to look like an ordinary vertical seismicsection.

• The traces from all of these vertical seismic sections can be presented aswiggle variable area, wiggle, variable density, color or combinations ofthese displays. On the workstation, generating these displays is easy andquick.



TIME SLICE DISPLAY

• The data volume may also be cut horizontally, extracting data samples atevery trace location at the same time value. An example of the resultingdisplay.

• A time slice may be extracted at any time in the data volume for which



• A time slice may be extracted at any time in the data volume for whichthere is a time sample value. Typically, data volumes are sampled at 4-millisecond intervals. Time slices are usually displayed in color variabledensity and time values are interpolated between individual trace locationsto make the display appear continuous.



TIME SLICE DISPLAY





COMPOSITE DISPLAY

• In viewing 3-D data, we are not limited to a single vertical or horizontal slicethrough the data volume. Composite displays, which combine severaldifferent slices, can also be extracted. Examples of composite displays areline/time (or chair) displays, cube displays and concertina displays.



• Line/time displays combine a vertical section and a time slice into a singledisplay. In other words, the vertical seismic section is cut by a time slice at aparticular time. Horizons on the two display segments tie perfectly due tothe nature of the 3-D data volume. These are often called chair displaysbecause they look like the back, seat, and front legs of a chair.



COMPOSITE DISPLAY





COMPOSITE DISPLAY

• A variation of a chair composite is a folded section display, which tiessections in the three (inline, crossline and time slice) orthogonal datavolume directions. These cube displays may be "unfolded," showing tyingsections as flat displays, or projected, showing three sides of the survey'sdata cube (Cube display).



data cube (Cube display).




The interpreter picks horizons and ties them across the sections of the


of the composite display, making these sections valuable for establishing continuity between lines.



CONCERTINA DISPLAY

• Another type of composite display is a concertina display. This display is theequivalent of hanging multiple paper sections on a wall to comparefeatures on each section. The concertina display uses multiple images oflines taken in parallel at some increment and is normally used to trackfeatures across multiple lines and to establish continuity within the data set.



features across multiple lines and to establish continuity within the data set.The concertina is also used to display several different processed versions ofthe same line.

• The example shown in Figure (Concertina) uses three different displays ofthe same inline.



CONCERTINA DISPLAY


The left-hand section is theapparent polarity of the inline,the center panel shows theregular amplitude and the rightpanel displays the reflectionstrength. In this example, the


strength. In this example, thereflection strength and apparentpolarity complex trace attributeswere computed in about fourseconds on a workstation fromthe regular amplitudes of theinline.



USING COLOR IN DISPLAYS


• Color is one of the attributes commonly associated with either 2-D or3-D data displayed on interactive interpretation workstations.

• Color enhances and highlights data to make it easier to understand.

• For color variable density displays such as maps or time slices, sample


• For color variable density displays such as maps or time slices, samplevalues are displayed as colored picture elements or pixels. Colors are assignedto sample the data so that the entire range of data values are displayed in colorswhich vary according to some scheme. Each pixel, therefore, represents a datasample of a particular value.

• For seismic data, the information conveyed is the same as that from awiggle trace, but if color is used, it is often easier to identify changes in theamplitude value of a peak or trough and distinguish it from its neighbors.



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Lecture of seismic

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