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`Ex. PGS 2003
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`Ex. PGS 2003
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`

`
`Designing Seismic Surveys
`in Two and Three Dimensions
`
`Dale G. Stone
`
`Edited by Charles A. Meeder
`
`Society of Exploration Geophysicists
`Post Office Box 702740 / Tulsa, Oklahoma 74170-2740
`
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`Ex. PGS 2003
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`

`
`Stone, Dale G., 1931-
`Designing surveys in two and three dimensions / Dale Stone.
`p. cm.
`(Geophysical references;v. 5)
`Includes bibliographical references.
`ISBN 1-56080-073-9:$67.00
`1. Seismic prospecting.
`TN269.8.S76
`1994
`550'.28--dc20
`
`I. Title.
`
`II. Series.
`
`94-27480
`CIP
`
`(Series)
`
`ISBN 0-931830-47-8
`ISBN 1-56080-073-9
`¸ 1994 by Society of Exploration Geophysicists
`All right reserved. This book or parts hereof may not be reproduced in any
`form without permission in writing from the publisher.
`
`1994
`Published
`Reprinted 1995, 1998
`Printed
`in the United States of America
`
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`
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`

`
`18
`
`Chapter 2: Sampling Theory
`
`adequate to prevent aliasing of the migration operator. The
`sampling theorem is modified by a dip of reflection term as
`
`Gn(cid:127)x = 0.5*(Y/fm) / sin @,
`
`where @ is the deviation from horizontal of the reflection.
`The modified equation gives the maximum size of the group
`interval which will not alias during the migration operation. Any
`interval smaller than this will be satisfactory. As the angle
`increases, the interval limit becomes smaller.
`The sampling theorem guides the survey design to adequately
`sample dipping and curved horizons for the processing to be
`applied later. The earth is variable in velocity in both dimensions.
`The velocity of the target layer or the deepest layer of interest is
`used in the calculation. Average velocity to the target horizon
`gives a more conservative estimate of Gma x. There are other
`complications, such as the spreading of the wavefront, which
`modify the sampling from the point on the surface to an area called
`the Fresnel zone at depth.
`
`Spread-length sampling
`
`The spread of geophones has a variable number of stations with
`96 or more channels typical in two dimensions. Multiplying the
`group interval by the number of receiver stations gives a line or
`spread length. This portion of the survey is sampled by the spread
`before it is moved. The line length must be at least as long as the
`depth of the deepest horizon of interest. This parameter is of most
`interest to those designing the survey. The sampling of the line
`length is mostly of concern to data processors when computing
`statics solutions. The length of the line is in the dimensions of
`miles. The wavelength of the line sampling is very long. Static
`solutions are then limited by what the practitioners call long-
`wavelength indeterminacy. The spread-length sampling does fit
`the sampling theorem but is not of immediate interest to the
`survey designer.
`
`Bin sampling
`
`For the 3-D survey, depth points are collected from a rectangular
`area. The eventual process is to sum the traces that fall into a bin.
`When this is done, the process becomes a discrete sampling and
`
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`Chapter 2: Sampling Theory
`
`19
`
`o o do ob
`o ß oo
`ß ß
`
`Center
`
`of bin summation
`
`F(cid:127)G. 15. For 3-D surveys, sampling is by bins. Traces falling
`within a bin are summed to establish the spatial sampling.
`
`falls within the application of the sampling theorem. Figure 15
`illustrates the sampling of the 3-D survey.
`The sampling theorem with the velocity and dip modification
`applies to the bin sampling. The difference is that there is now a
`directionality to the sampling. This directionality relates to the
`angle factor. In a 2-D survey, the angle between source and receiver
`is zero. For a 3-D spread as in Figure 15, there is a unique azimuth
`from source to the bin center. The in-line and cross-line directions are
`used to check the bin size for fitting the sampling theorem.
`The modeling process for assistance in designing surveys has
`other concerns for sampling. One such concern is the ability to
`discern the top and bottom of a reflective layer in the seismogram.
`A general agreement is that the frequency of the wavefront must
`have a wavelength that is less than half the thickness of the layer.
`
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`20
`
`Chapter 2: Sampling Theory
`
`Dissenting opinions state that a quarter wavelength is required for
`sampling in time, which allows resolution of the top and bottom of
`the layer.
`Most survey parameters relate directly to the sampling theorem,
`which is a basic building block for survey design. Higher frequen-
`cies, lower velocities, and angularity are factors that require
`smaller sampling intervals. The design of arrays, group intervals,
`bin size, and resolution depends on the theorem.
`
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`
`Chapter 6
`
`BASIC CONCEPTS
`
`IN 3-D SURVEYS
`
`There are some new aspects to the survey design in three
`dimensions relative to 2-D surveys. The 2-D surveys are as linear
`as the terrain allows. Source and receiver are normally in-line
`with each other. Arrays may be multidimensional, but most often
`are also in the line of the survey. For 3-D surveys, this is seldom
`the case.
`The source interval of a 2-D survey must be extended to include
`a definition of the source line. When the sources are in-line, the
`source line overlays the receiver line, so only the source interval
`needs to be determined. This is not the case for 3-D surveys, and a
`source line must be defined. In the most used designs, the source
`line is now orthogonal to the receiver lines, as in Figure 65.
`Note that the receiver line becomes the receiver lines. As many
`receiver lines are laid out as the equipment for acquisition allows.
`Also, the receiver layout may not be lines but circles, checker-
`boards, and other patterns developed for 3-D surveys. Thus the
`simple parameters that defined the traditional 2-D line now must
`be extended to include much more geometry, more than you may
`be able to do on the back of an envelope, as was the case for 2-D
`lines.
`The 3-D survey also includes multiple source lines as well as
`multiple receiver lines, and it is possible to record two source lines
`simultaneously using vibration techniques. The arrays also may
`respond in a less predictable manner as they are not necessarily in
`line with either the source or receiver locations. If the survey is
`planned to acquire a good directional range of offsets, the arrays
`will see the oncoming wavefront from a number of angles. This will
`require a more sophisticated analysis of the array effect. Use of
`star patterns and other multiazimuth array patterns is sometimes
`practiced. Figure 66 shows that the orthogonal source line strikes
`linear arrays at an angle.
`The analysis of 2-D designs centers on the subsurface coverage
`
`87
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`88
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`RECEIVER
`
`LINES
`
`tSOURCES
`
`FIG. 65. The source line is perpendicular to the receiver
`lines.
`
`in the form of common-depth-points (CDPs). For 3-D surveys, the
`CDP becomes two dimensional and is termed a bin. These bins may
`be square or rectangular and define the spatial resolution of the
`data sampling. Indeed, deciding the bin size will be the first step in
`designing a 3-D template. Subsurface sampling will be, as with the
`CDP, half the surface size. An example of bins is shown in
`Figure 6 7.
`The accent of 2-D lines is on the fold of coverage and the offset
`range. For 3-D survey, the fold may be less, but the azimuth range
`is added to the offset range as a parameter. If structure is complex,
`
`R
`
`array
`
`S
`
`FIG. 66. Wavefronts strike linear arrays at an angle.
`
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`Chapter 6: Basic Concepts in 3-D Surveys
`
`89
`
`FIG. 67. Bins form the basic building block for 3-D
`surveys.
`
`then good azimuthal range becomes more important. In Figure 67
`there may be some arbitrary number of seismic traces in a bin. For
`velocity analysis, the bin needs to contain a range of offsets. Where
`structure is complex, the analysis must include an azimuthal
`property. The range of azimuths in the bin is also a consideration.
`In a given bin, there may be more or less traces than the desired
`fold. Re-binning is sometimes used in data processing to make the
`fold more consistent.
`The concept of azimuths also is a new factor in 3-D surveys. The
`usual 2-D lines vary from receiving energy in-line with in-line
`arrays only when there are obstacles. The designs of 3-D surveys
`usually result in a bin receiving the source wavefront at a variety
`of angles. The swath survey in Figure 68 shows some of the
`arrivals to a receiver point.
`This azimuthal property is not significant when the geology
`features only gentle dips and lateral consistency. The effect of dip
`is to increase apparent velocity. Thus, velocity analysis must have
`an azimuthal property. The imaging of complex structure is also
`improved by surveys with a good range of azimuths.
`Another new factor is the use of computers to do the design.
`Moreover, interpretation is usually conducted on work stations.
`The multiple source and receiver lines, the difficulty of computing
`
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`90
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`FIG. 68. A given receiver point receives arrivals from many
`directions.
`
`fold coverage, azimuthal distribution, and offset ranges in the bins
`make the use of a computer program to aid in design almost a
`necessity. Those skilled in 2-D surveys can make all the calcula-
`tions by hand in less than an hour and usually with the aid of a
`calculator. A 3-D design for marine work is often possible with just
`a desktop personal computer. Most land surveys can also be done
`on the PC-type computer. For large land surveys involving com-
`plicated patterns, larger mainframe computers capable of large-
`scale graphical output are more suitable. Some systems are capa-
`ble of overlaying the design on satellite photos or maps using a
`large-screen monitor for interactive design. Global positioning
`systems and geodetic elevation measurements make the maps very
`accurate.
`in three
`zone takes on some new characteristics
`The Fresnel
`dimensions. Generally, even in two dimensions, this important
`concept is given a small amount of attention. As the target sizes
`historically decrease in size, the zone becomes more important.
`Lindsey (1991) gives an excellent review, and some of his concepts
`are discussed here. Figure 69 illustrates the Fresnel zone as it
`expands with depth.
`Essentially, the theoretical point source expands as it propa-
`gates in depth, "illuminating" a circular area at vertical incidence.
`In a seismic context, this is the reflecting surface constructively
`contributing to the reflection. A good approximation to the radius
`of the zone is
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`Chapter 6: Basic Concepts in 3-D Surveys
`
`91
`
`Fi(cid:127). 69. The Fresnel zone of a
`propagating seismic wavefront.
`
`R = (Z/F)(cid:127)/2,
`
`which shows that the zone increases in radius with depth but
`decreases with higher frequency wavefronts. Migration serves to
`reduce the zone to some minimal size when accurately done and
`the data fits the assumptions.
`It should be noted that when the reflecting point is offset, the
`circle becomes elliptical. This angular effect actually reduces the
`size of the zone along the minor axis of the elliptical response. Dip
`and structure also are factors in the actual response.
`For a fiat surface, the following is a simple formula using the
`velocity, arrival time, and the time from the peak-to-zero crossing
`of the wavelet being propagated. These are parameters more
`familiar to geophysicists.
`
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`92
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`800
`
`ft.
`
`F(cid:127). 70. Closely spaced seismic targets and the Fresnel zone.
`
`R = V(TtF
`
`where V = average velocity to the event, T = arrival time, and
`t - peak-to-zero crossing of the wavelet.
`This formula is related to the previous one in that the "t" term
`is inversely proportional to frequency. The higher the frequency,
`the smaller
`t becomes. The size of the zone then
`increases with
`velocity and arrival time, another form for the depth, and de-
`creases with the frequency. For example, consider an event at 1.0 s
`with a velocity of 8000 ft/s and a wavelet half breadth of 0.125 s
`which implies a zone of 894.3 ft. As in Figure 70, earth structures
`of a size or spacing less than 894 ft cannot be individually
`absolutely distinguished. For a normal trace spacing of 110 ft in
`the stack section, events closer than eight traces cannot be dis-
`criminated. In some cases, this would not be a meaningful param-
`eter. For the reef exploration in the example in Chapter 3, which
`shows two reefs actually on the target horizon, the discrimination
`could be less than desired.
`There is a rather lengthy formula that allows computation of the
`size of the Fresnel zone as a function of the offset distance, angle of
`the reflector, velocity, and frequency. For acquisition design, the
`simpler formulas above generally approximate the only parameter
`under the control of the designer. The depth of the target and the
`velocity of the stratigraphy are not things that can be controlled.
`Only the frequency of the seismic source can be altered, and that
`is limited by the parameters of the earth itself. The sweep range
`for vibratory sources and the charge size of explosive sources are
`design parameters. Estimation of the size then indicates what the
`highest frequency needs to be to clearly discriminate small targets.
`Many seismic targets have structure and are three dimensional.
`
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`Chapter 6: Basic Concepts in 3-D Surveys
`
`93
`
`The Fresnel zone is sensitive to the size and shape of the targets.
`In 3-D surveys, with the many valued directions of reflection and
`ranges, allowance can be made for the form of the target.
`The behavior of the Fresnel zone is not the same on anticlines
`and synclines. The radius of curvature also is a factor. The
`formula, F- V(Tt) (cid:127)/2, is modified by a function of the radius of
`curvature.
`Let
`
`where R is the radius of curvature of the target. The K factor
`becomes smaller with smaller structures and larger with depth. K
`modifies the size of the zone differently for concave and convex
`forms, as shown in Figure 71. For the anticline, the modifying
`factor is 1/(1 + K). Thus the Fresnel zone becomes smaller
`for
`reefs and other local paleohighs. The synclinal structures are
`modified by 1/(1 - K) so that the radius becomes larger.
`The Fresnel zone is then an effect that can be modified by offset,
`frequency, depth, size, and structural character. For relatively fiat
`targets that are stratigraphic in nature, the parameter is not very
`crucial. When the target is small or features several zones of
`porosity, it has some meaning to the survey design.
`The really important aspect of 3-D data and Fresnel zones is the
`extra dimension of focusing possible with migration. Figure 72
`illustrates this compression. The implication is that smaller events
`can be resolved in three dimensions for the same input frequency
`range that is a significant design parameter.
`
`T ((cid:127)
`
`(cid:127)
`
`3-D Fresnel Zone
`Fb-V(Tt) "'
`
`K-z/R
`
`R-radius
`
`of curvature
`
`Anticline-Fb*(1/1.K)
`
`Syncline-F b*(1/1-K)
`
`Smaller
`
`Larger
`
`F(cid:127). 71. Structural effects on the Fresnel zone (used with
`permission from Lindsey, 1991).
`
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`
`94
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`Fresnel
`
`2-D
`
`3-D
`
`FIG. 72. Migration reduces the Fresnel zone in both dimensions
`on 3-D data. The resolution is improved by focusing out of plane
`energy and the S/N ratio is also increased.
`
`Preliminary basic parameters
`
`There are some parameters that need to be estimated as input
`when designing the 3-D survey. The physics and concepts are
`somewhat independent of whether the survey is to have two or three
`dimensions or just involve some modification to their calculation.
`
`imaging of shallow, target, and deep horizons still
`Offset.--The
`requires certain offsets of source and receiver. The calculation and
`direction may be different but the rules were developed in 2-D
`exploration. An approximation to the required offset for a given
`horizon is very simple and used often when surveys are designed in
`the field:
`
`Offset = depth of the horizon.
`
`More exact formulas are given in Chapter 4 for the near and far
`offsets. New factors include the fact that the offset may now be
`measured at an angle and the depth is now that of a plane rather
`than a line.
`
`Fold.--The fold required for noise compression is a function of
`the local S/N conditions. This translates
`in 3-D to the number of
`traces in a bin. Because of the extra focusing by migration and the
`flexibility of binning, fold can be less than required in 2-D surveys.
`Field tests or existing 2-D seismic data can yield an estimate of the
`needed fold for the 3-D survey.
`
`temporal frequency required is not much
`Frequency.--The
`different from that for 2-D surveys. The rules for the resolution of
`
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`Chapter 6: Basic Concepts in 3-D Surveys
`
`95
`
`layer of given thicknesses are best determined by modeling. The
`general rule is that the resolution of a thin bed requires it to be
`sampled twice with a quarter wavelength of the highest frequency.
`The field approximation was that the record time divided into 150
`estimates the frequency expected. Modeling, which includes the
`waveform, is suggested for thin beds. The modeling does now need
`to be three dimensional, so as to include structural effects.
`
`this point, it is relevant to remember that when
`Migration.--At
`dipping beds are in the preliminary model of the survey, the extent
`of the survey must be increased. The tangent of the angle of
`maximum dip modifies the areal extent of the survey. This is more
`important in three dimensions because of the expense of the survey
`and the increased migration power.
`
`Objectives of the survey
`
`The gathering of information is one of the basics essential to a
`successful survey. The most important information is defining the
`objectives of the survey. Although this seems a rather obvious
`comment, many times the objectives of the survey are not part of
`the input to design. The survey may be put out for bidding with
`little specification except for the areal extent and approximate
`spatial sampling. Requirements of good fold on a shallow reference
`layer or a deep reflection for indirect indicators may not be in the
`design input. One possible outcome is that the lowest bid is chosen
`and does not meet these objectives. This can, in some cases, make
`the data next to worthless. Design cannot begin until the objec-
`tives of the survey are clearly stated. As an example: "Map the top
`and bottom of the Austin Chalk formation at 6000 ft, which is
`generally 700 ft thick. The basement reflection should be imaged
`because basement folding is an indirect indication of chalk frac-
`ture systems which are the potential reservoirs."
`This information can be used in the parameter modeling for
`frequency and offset distances. No shallow horizon was specified.
`The implication is that the very shallow data are not important
`and that static corrections are likely not severe. If statics are a
`problem, a shallow horizon to fiducia!ize upon would be needed.
`"The fractured reservoirs are often accompanied by small faults.
`The self-contained fracture swarms may have another target as
`close as 200 ft. Spatial sampling should strive to allow discrimi-
`nation."
`This objective relates to the group interval specifically and
`indirectly to the Fresnel zone after migration. Modeling and
`
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`96
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`analysis will be needed during the design to determine the prac-
`ticality of such resolution.
`Stating of the survey objectives may save disappointment later
`when the time comes to interpret the 3-D data. Because 3-D data
`are more expensive than 2-D data, clarification of the objectives
`before survey design begins is especially important.
`
`Seismic data input
`
`The most directly useful input is existing seismic data. The
`seismic sections give information about many of the design param-
`eters such as noise, source power, weathering problems, and
`general structure.
`
`the field records and final stack for environmen-
`Noise.--Check
`tal and source-generated noise conditions. If noise conditions are
`present on the field records and suppressed on the stack section,
`note the related survey design and processing parameters. In
`particular, check the array design for possible use in the 3-D
`survey. There are areas where neither source nor environmental
`noise is a problem, which greatly simplifies the survey design and
`makes the whole project less expensive. Is the data still noisy even
`after stacking? Will higher fold solve the problem?
`
`type of source was used and what are the
`Source power.(cid:127)What
`power figures in pounds or pounds per square inch? Are the
`reflections at depth clearly discernible or is more source energy
`needed? Are the shallow data lacking high frequencies because of
`sweep rate or excessive source energy? Does the environment
`dictate the type of source? Some surveys involve both land and
`marine or swamp. If so, the use of different sources or receivers in
`the same survey may be dictated. As with 2-D surveys, the best
`answer is from field tests. When tests cannot be done, the existing
`seismogram is the best source of reference.
`
`extensive static corrections made
`Weathering problems.--If
`during processing indicate problems in the near surface, note this
`on the survey design. Statics are an even more difficult problem in
`3-D surveys. Any refraction surveys done are helpful and consid-
`eration could be given to some control refraction lines. The design
`of the survey can reduce processing problems in many cases. The
`data processing department should properly be a part of the survey
`design team.
`
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`Chapter 6: Basic Concepts in 3-D Surveys
`
`97
`
`FIG. 73. A seismogram with significant structural complexity.
`The complex structure will influence the choice of recording
`templates for the 3-D survey.
`
`the seismogram for structure.
`General structure.--Examine
`Are there dipping or curved layers? When there is structure as
`shown in Figure 73, the migration aperture requires extending the
`survey size and also affects other parameters.
`The domal structure means that a good range of source-receiver
`azimuths will be helpful in defining the shape of the structure. The
`maximum dip is a parameter to many of the calculations in 2-D
`surveys and also applies to 3-D surveys. The dip can be estimated
`from the seismogram modified by the relevance to target horizon.
`Shooting with dip or strike in 2-D surveys is a consideration. For
`properly sampled 3-D surveys, direction is no longer considered to
`be as important as achieving a good azimuthal range.
`Wherever possible, horizons on the seismogram should be iden-
`tified which may require help from the interpreter most familiar
`with the area. Correlation to existing wells can also be helpful in
`identification. The seismogram can also furnish information for
`input to modeling and ray-tracing programs. When the structure
`appears very complex, an extra 2-D line will make velocity
`analysis more reliable.
`
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`
`98
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`.(cid:127) :J-,](cid:127) VELOCITY
`[ CHARTS
`
`TYPE
`(cid:127)
`
`fiFCT'ON
`:
`Ixq800(cid:127)..TYF
`S(cid:127)ff HW F_5'T
`._
`
`(cid:127)
`
`. .(cid:127)..(cid:127) ....... (cid:127)-(cid:127)--; ........ ! ........ (cid:127) .......
`
`
`
`." (cid:127) .---(cid:127) ....... :-,; ......... :-,---(cid:127)--r"i;"(cid:127)"
`..:;
`.
`t
`- .
`
`ß .'. ,.: ": .......... t: .......... (cid:127) ........... :"'
`
`
`'(cid:127)' (cid:127): ............... (cid:127) .............. : ....... i ......
`
`
`
`, .(cid:127);,(cid:127)....; .......... (cid:127) .......... ,: ....
`
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`
`
`
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`
`
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`
`.
`
`
`
`from the seis-
`information
`74. Gather
`F(cid:127).
`mic section labels. The labels usually con-
`tain velocity charts, filters, the processing
`parameters developed for the 2-D data, ge-
`ometry, and arrays for the area.
`
`The seismogram allows a visual evaluation of the S/N ratio and
`the fold used to achieve the result. An estimate
`is that half the 2-D
`fold will achieve the same S/N in 3-D data. Field tests provide a
`more applicable fold estimate and should be performed whenever
`possible.
`Another obvious but important task is to read the label of the
`seismogram. The side and top labels on the seismic section contain
`a wealth of useful information as shown in Figure 74. Check the
`instrumental filters applied, type of geophones, and all the acqui-
`sition parameters. Study the data-processing flow particularly,
`including the filter and polarity conventions. More modern dis-
`plays attempt to define the polarity of the display. For strati-
`graphic targets, this may be very important in correctly identify-
`ing the top of the target horizon. The polarity is also important in
`correlating the seismogram to well log and VSP data.
`
`Downloaded 01/31/15 to 173.226.64.254. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/
`
`Ex. PGS 2003
`
`

`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`99
`
`The elevation profile at the top of the seismic section label
`should be inspected for any correlation with the apparent struc-
`ture. Changes in the elevation correlating to apparent structural
`changes are always suspect. The top of the label also contains the
`velocity charts used in processing. This velocity information is
`helpful in estimating the depths of important horizons for input to
`the survey design equations as well as model building. A discus-
`sion with the data processor is often helpful.
`Hindsight is always better, and evaluating the results of the 2-D
`survey parameters and processing can often give insight into more
`effective parameters for the 3-D survey. The seismogram and its
`label also furnish most of the parameters used for design modeling.
`When seismic data is available, the seismic section is the best
`source of information for the 3-D survey design.
`
`Borehole
`
`data
`
`In some areas, there may be logged wells. Logs contain an
`accurate record of the depth of horizons and may also be verified by
`core samples. For survey design, identification and depths of
`horizons are the relevant information to be extracted. Velocity
`logs, however, are not always perfect; therefore conversion to time
`does not always result in a clear cut match to the seismic data. The
`usual procedure is to make a synthetic seismogram. The velocity
`log is differentiated to give the reflection coefficients and the
`velocity is used to map the depth function to time. The variable is
`the wavelet used in filtering the reflection coefficients to simulate
`the bandwidth of the seismic wavelet. The seismogram is accurate
`on arrival times and the logs on depths, but the two do not always
`match well enough to positively identify horizons.
`The link between the seismogram and the log is the vertical
`seismic profile (VSP), when available. The receiver is at a known
`depth in the borehole, and the arrival time of direct waves gives a
`firm connection of time and depth. The VSP also may have a
`higher frequency content than the seismogram, since VSP is a
`one-way rather than a two-way traverse of the earth. The VSP
`thus provides a correlation of time and depth so that the target
`horizons can be readily and confidently identified on the seismo-
`gram. It is very reassuring when the log, VSP, and seismogram
`correlate well as in Figure 75.
`Such good correlation is not really necessary for survey design.
`Approximate knowledge of the velocity and depth of target and
`support horizons is adequate for most of the design criteria. Of
`course, the thickness of the target shown on the displays is helpful
`
`Downloaded 01/31/15 to 173.226.64.254. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/
`
`Ex. PGS 2003
`
`

`
`100
`
`Chapter 6: Basic Concepts in 3-D Surveys
`
`FIG. 75. A well log synthetic inserted into a seismogram. The
`well log has detailed velocity and depth information important to
`survey design (from Boisse, 1978).
`
`for modeling of frequency requirements and spatial sampling
`parameters.
`In summary, borehole data can provide information on identifi-
`cation, depths, and velocity of the horizons of interest.
`
`Scouting
`
`involves traveling over the proposed
`Scouting traditionally
`survey by vehi