Lecture-06 March 20 2015 Friday

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 20, 2015 (Friday)March 20, 2015 (Friday) Lecture # 6Lecture # 6Lecture # 6Lecture # 6



3-D SEISMIC INTERPRETATION


(Interpretation Workstations)



INTERPRETATION WORKSTATIONS

• Computer workstations are an essential part of the interpretationprocess for 3-D data because they allow the interpreter to manipulate datarapidly in order to make a good 3-D interpretation possible.

• To establish a common understanding of the nature and operation ofan interpretation workstation, we will first present an overview of some of thehardware and software capabilities offered by workstations.


hardware and software capabilities offered by workstations.

• Most computerized seismic interpretation systems were conceivedinitially to deal with the massive amounts of data concentrated in a 3-D survey.

• Unlike traditional 2-D surveys which include some tens of lines, amodest-sized 3-D survey can easily contain 300 inlines of 1,000 traces each andsix seconds of data sampled at 4-millisecond intervals




• The computer performs all of the "data management" for the 3-D dataset by keeping track of all the seismic displays, mapping coordinates, syntheticwell data, interpreted horizons and fault picks.

• Displays can be generated for any line or combination of lines, in anyorder. This is accomplished much more easily on the computer than fightingthrough a stack of paper, folding lines at tie points, or waiting for new paper


through a stack of paper, folding lines at tie points, or waiting for new papersections to be printed.

• The interpreter can also view the structural interpretation as three-dimensional surfaces or as contour maps, making it much easier to visualizewhat the prospect really looks like.

• In addition, most interpretation software offers quality controlalgorithms that allow the interpreter to isolate and correct interpretation errors.Thus, a better interpretation is created on the computer than might be possibleon paper.




• Workstation seismic interpretation programs offer a number of specialcapabilities that make working with the seismic data easier, speed up theinterpretation process, and enhance the quality and accuracy of theinterpretation.

• These capabilities help the interpreter solve problems in areas ofambiguous or poor data, pick seismic data more accurately, and rapidly


ambiguous or poor data, pick seismic data more accurately, and rapidlygenerate different displays to use as quality control when interpreting theseismic data.



INTERPRETATION WORKSTATIONSAutomated Horizon Picking

• One special capability that speeds the interpretation process is theautomated horizon picker. Horizon picker algorithms interpret seismic horizonsby extrapolating from and interpolating between a few interpreted points onthe horizon. In general, horizon picker software programs are either semi-automatic or fully automatic.


automatic or fully automatic.

• Semi-automatic horizon pickers allow you to interpret a series ofguide points (or seed points) along a horizon. The program then interpolatesthe horizon between these points. This system requires continual interactionbetween the interpreter, who selects the guide points, and the computer, whichfills in the intervening points.




• Fully automatic horizon pickers usually require only one startingpoint to identify the horizon.

• After this point is selected, the computer completes picking thehorizon on the selected line(s) by extrapolating from this initial point.


horizon on the selected line(s) by extrapolating from this initial point.

• Most automatic pickers use a defined "window," within which thesystem searches for the next trace correlation for the horizon being picked.

• These correlations may be based on criteria as simple as the highestamplitude peak or trough, depending on which phase of the horizon reflector isbeing picked. For common "coherency" picking, the maximum amplitude isselected as the guide point for extending the horizon.




• Thin-bed cross-correlation pickers use a cross-correlation functionto find the best fit between the trace being examined and a model trace,composed of traces which have already been picked, or the last trace picked.This works well in areas where thin beds and tuning phenomena mightotherwise obscure the picks.


otherwise obscure the picks.

• Areal pickers extend the interpretation of a horizon to multiple lines,crosslines, and time slices, with limited interpreter intervention. These are also

called spatial automatic pickers because they interpret horizons across anentire data set automatically.



INTERPRETATION WORKSTATIONSComplex Trace Attributes

• Complex trace attribute offer an important way to view data andisolate features which might otherwise not be apparent.

• This display is calculated for portions of lines or for entire lines andgenerally contains the three attributes of instantaneous phase, instantaneous


generally contains the three attributes of instantaneous phase, instantaneousfrequency and reflection strength.

• The instantaneous phase attribute is valuable for highlighting eventcontinuity and emphasizing discontinuities such as faults.

• Instantaneous frequency is often used to isolate direct hydrocarboneffects which show loss of high frequencies.

• Reflection strength identifies other properties of reflecting horizons.



INTERPRETATION WORKSTATIONSMovies

• One valuable capability offered by 3-D interpretation workstationsthat is often overlooked by interpreters is the ability to animate data usingmovies. Such movies consist of a series of "snapshots" or frames of data takenalong a common direction that allows the interpreter to move through the datavolume in discrete intervals.


volume in discrete intervals.

• The frames are shown one after another, thereby giving the illusion ofmotion through the data volume.

• By watching how horizons move over time and distance, the interpretercan refine his or her understanding of what a structure looks like, how it isfaulted and how it should be interpreted.



INTERPRETATION WORKSTATIONSStructure Flattening & Parallel Extraction

• Horizon flattening is a method for partially restoring a seismichorizon to what it might have looked like prior to post-depositionaldeformation.

• After selecting and picking a horizon to flatten, the surrounding dataare effectively shifted to show what they might have looked like at the time the


are effectively shifted to show what they might have looked like at the time thehorizon was laid down. Flattening can be done in one of two forms ;

• Single-section flattening• Volume shifting

• The usual method is to flatten lines one at a time. To flatten on a singleline, the interpreter selects a horizon on which to flatten and the time at whichto place the flattened horizon. The section is then shifted to make the selectedhorizon flat. On most systems, if you pick data on the flattened sections, thetrace-by-trace time shifts are applied to the picks so that they will be correctlystored in the interpretation database.




• For volume shifting, the interpreter selects a horizon that has beenfully picked and gridded. All of the traces in the data volume are then shifted tomake the selected horizon surface flat.





Parallel Extraction• A related capability uses an interpreted surface to extract data along a

surface parallel to it at some delta time or delta depth. This is called parallelextraction or, more popularly, horizon slicing. Parallel extraction is akin tovolume shifting, but is less numerically intensive.


volume shifting, but is less numerically intensive.

• Again, the interpreter starts with a picked and gridded surface. Then, somedifferential time (delta t) above or below the surface is specified. The systemextracts data samples at the delta time from the original surface and displaysthem like a time slice.

• In essence, the new data display is parallel to the original surface andlooks like a time slice from a flattened data volume at that delta time from theoriginal surface.



ThanksThanks


ThanksThanks

Lecture-06 March 20 2015 Friday

Documents

interpretation software

seismic data easier

d interpretation possible

structural interpretation

better interpretation

karachi campus3d seismic

bahria university

seismic displays