Converted Wave Processing

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GEOPHYSICS, VOL. 67, NO. 5 (SEPTEMBER-OCTOBER 2002); P. 13481363, 18 FIGS.10.1190/1.1512781

Tutorial

Converted-wave seismic exploration: Methods

Robert R. Stewart, James E. Gaiser, R. James Brown,and Don C. Lawton

ABSTRACT

Multicomponent seismic recording (measurementwith vertical- and horizontal-component geophonesand possibly a hydrophone or microphone) captures theseismic wavefield more completely than conventionalsingle-element techniques. In the last several years, mul-ticomponent surveying has developed rapidly, allowingcreation of converted-wave or P-S images. These makeuse of downgoing P-waves that convert on reflection attheir deepest point of penetration to upcoming S-waves.Survey designfor acquiringP-S data is similar to that forP-waves, but must take into account subsurfaceVP/VSvalues and the asymmetric P-S ray path. P-S surveysuse conventional sources, but require several times

more recording channels per receiving location. Somespecial processes for P-S analysis include anisotropicrotations, S-wave receiver statics, asymmetric andanisotropic binning, nonhyperbolic velocity analysisand NMO correction, P-S to P-P time transformation,P-S dip moveout, prestack migration with two velocitiesand wavefields, and stacking velocity and reflectivityinversion for S-wave velocities.

Current P-S sections are approaching (and in somecases exceeding) the quality of conventional P-P seismicdata. Interpretation of P-S sections uses full elastic raytracing, synthetic seismograms, correlation with P-wavesections, and depth migration. Development of the P-Smethod has taken about 20 years, but has now becomecommercially viable.

BACKGROUND

The primary method of hydrocarbon exploration remainsP-wave seismic reflection surveyingand for good reason.Among all the elastic waves, compressional waves arrive first,usually have high signal-to-noise ratios, have particle motionthat is close to rectilinear, are easily generated by a variety ofsources, and propagate in fluid environments. We expect thatP-wave reflection surveying will be the dominant explorationmethod for some years to come, but several questions are ger-mane. Canwe improve P-wave pictures?Can we generateaddi-tional or augmenting images using the seismic method? WhenP-wave surveying fails, can we use other seismic techniques?

Perhaps the most straightforward answer to these questionsis, Yes, try multicomponent recording and analysis. There isconsiderable promise in using multicomponent recordings toimprove P-wave sections themselves. However, the thrust of

Manuscript received by the Editor February 2, 2000; revised manuscript received February 28, 2002.CREWES Project, Universityof Calgary, Department of Geology and Geophysics, 2500 UniversityDrive N.W., Calgary, Alberta T2N 1N4,Canada.E-mail: [email protected]; [email protected], 1625 Broadway, Denver, Colorado, 80202.c 2002 Society of Exploration Geophysicists. All rights reserved.

this paper is to provide a tutorial on using multicomponentdata to create images from another mode of seismic energy:the converted shear waves.

In using the term converted-wave exploration, we imply aparticular conversion: a downward-propagating P-wave, con-verting on reflection at its deepest point of penetration to anupward-propagating S-wave (see Figure 1). There are manyother types of energy conversion that may occur as seismicwaves move through the earth. In relatively high-velocity lay-ers (such as permafrost, volcanics, or salt), there may be anS-wave leg generatedin the downgoingpath that convertsfromand then back to a P-wave. In the marine case, we might havea P-to-S downgoing transmission at the ocean bottom that will

eventually reflect as an S-wave and reconvert to a P-wave atthe ocean floor (Tatham, 1982). Nevertheless, modeling andfield measurements show that transmitted or multiple conver-sions generally have much lower amplitudes than the primary

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Converted-wave Seismic Exploration: Methods 1349

P-to-S reflection, that is, P down, S up (Rodriguez, 2000). Wewill focus only on this P-S conversion. We note here (Figure 1)that there is an asymmetry in the P-S raypath as described bySnells law: sin /VP =sin /VS, whereand are the P- andS-wave angles of incidence and reflection, respectively, andVPand VS are the P- and S-wave velocities, respectively. Since

VS< VP , is less than , and the S-wave leaves the interfacecloser to perpendicular than the incident P-wave.

Whereas Snells law gives the basic geometry of the ray-paths, the Zoeppritzequationsprovidethe amplitude of the re-flections. In general, a P-wave incident on an interface betweentwo elastic media will generate a shear-wave reflection. Forthe single interface of Figure 2, we can see a quasi-sinusoidalvariation with offset in the converted-wave reflectivity (forinteractive calculation of Zoeppritz P-P and P-S reflectivitysee http://www.crewes.org/Samples). This energy partitioningis part of the reason why there are amplitude-variation-with-offset (AVO) effects in P-wave data. Aki and Richards (1980)show that the P-S reflectivity, RPS, can be approximated (as-suming property changes are small) by

RPS = k

(1 + )

+ 2VS

VS

, (1)

wherek = (tan )/2, = 2(sin2 )/2 + 2(cos cos )/,= VP/VS, =lower upper, VS= VSlower VSupper, =

12

(lower +upper),VS=12

(VSlower + VSupper), andVP =12

(VPlower +VPupper).

There are three notable aspects to equation (1): it has no ex-plicit dependence on P-wave velocity change, it is negative upto moderate angles for positive parameter changes and, gen-erally, it indicates that there is P-S energy, at moderate angles,comparable to the corresponding P-P energy (Figure 2).

So, we now have the two basic aspects of P-S wave prop-agation: asymmetric ray paths according to Snells law, andsinusoidal amplitude variation with offset as described by theZoeppritz equations.

Concentrated work in P-S analysis has been proceeding forabout 20 years; several commercial acquisition and processinggroups are now active. We might compare this with the de-

FIG. 1. A converted-wave (P-S) reflection at its conversionpoint (CP) compared to a pure P-wave reflection at its mid-point (MP). Note the CP is shifted toward the receiver. TheP-wave angle of incidence and S-wave angle of reflection aregiven by and , respectively. Directions of positive phase,as shown by arrowheads, are according to Aki and Richards(1980).

velopment of 3-D seismology using P-waves. The 3-D seismicconcept and early experimentation began in the 1960s, theoryand processing were largely worked out in the 1970s, and theirapplication came in the 1980sabout 20 years from conceptto common practice. P-S surveying was proposed and tried inthe late 1970s, with processing fundamentals developed in the

1980s to early 1990s. Assuming that P-S surveying is on a sim-ilar track to that of 3-D seismic analysis, we would expect itto become common practice in the next several years. Excitingresults are coming in, but the overall evaluation of the methodis still in progress (Duey, 2001).

We might inquire why multicomponent, and especially P-S,methodologies havent been widely used in hydrocarbon ex-ploration in the past (as opposed to common multicomponentusage in earthquake studies). There would seem to be sev-eral reasons for this. In the acquisition world of several yearsago, multicomponent sensors were not available in large num-bers. On land, there were challenging logistics in planting andcabling them, and in recording their output, which requiresthree times the normal number of channels per station. Four-component marine sensors (three orthogonal geophone ele-

ments and a hydrophone) were rare. Converted-wave surveydesign was not well understood, and design software not com-mercially available.

Processing P-Swaveswas also problematic.Much of thethe-oryfor processing thedata hadnot been workedout, andtherewere subsequent delays in development of software and expe-rienced personnel. Oneof theprocessing stumblingblocks wasthe variation of the P-S reflection points in depth for any givensource-receiver offseta result of unequal P-incidence andS-reflection angles (Figure3). Gathering, mapping,and binningforP-S data were (and are) more complicated than in P-Panal-ysis with its straightforward common-midpoint assumption.

Furthermore,interpreting P-S data was difficult because fewS-wave velocity logs had been acquired and P-S synthetic seis-mograms were not available. On top of all this, P-P and P-S

sections displayed events, from the same reflector, at different

FIG. 2. P-Pand P-Splane-wave reflectioncoefficientsas a func-tion of P-wave angle of incidence. Note that the absolute valueof the P-S reflection coefficient is plotted. The S-wave veloci-ties for the upper and lower layers are 1750 m/s and 2650 m/s,respectively. Density is constant.


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(Rider, 1996) and perhaps pore geometry. For example, Millerand Stewart (1990) use data from full-waveform sonic logsin the Medicine River field in Alberta, Canada, to analyzeVP/VS values from pure lithologies (sandstone, shale, lime-stone; Figure 4a). Similar to values reported by other authors,theirVP/VSvalues forsandstoneclusteraround1.6, withhigher

values near 1.9 for shale and limestone. When the lithologiesbecome mixed or complex, theVP/VSvalues change to moreintermediate quantities (Figure 4b).

Miller(1996)also showswell-logvaluesfrom a field in south-ern Alberta (Figure 5). The Glauconitic sandstone reservoirshows significantly higher VSvalues than do the off-reservoirshales at the same depth. Thus, we expect a decrease inVP/VSfrom regional shales to reservoir sand. We can also plot thesedata asVP/VSversus gamma-ray values. Generally, there is asmall increase inVP/VSfor sands with more clay or shaliness.

In another analysis of an array sonic log [from the Daveywell (3-13-34-29W4) in central Alberta, Canada] Miller (1996)plottedVP/VSvalues, photoelectric factor (PEF) curves, andanhydrite fraction. The other primary lithology was dolomite.Recall that the PEF or photoelectric absorption is strongly de-

pendent onthe averageatomic numberof theformationand byinference the lithology (Rider, 1996). Miller (1996) noted thatVP/VS values from thearray-sonic trackthe PEFcurve andvol-ume of anhydrite quite well: as the anhydrite-versus-dolomitefraction increases, so do the VP/VSand PEF logs. Anhydrite

FIG.4. (a) Well-logVP/VSvalues versusVP for pure lithologies of the Medicine River field. (b)VP/VSvalue versus VP for mixedlithologies (from Miller and Stewart, 1990). SS = sandstone, SH = shale, and LS = limestone. Nordegg, Detrital, and Shunda arelithostratigraphic units.

FIG.5. (a)VS versusVP values from well logs for a sand reservoir and off-reservoir shale.VSis significantly higher in sand than inshale in these wells (Miller, 1996). (b)VP/VSvalue versus gamma-ray value from well logs as in (a). VP/VSshows a slight increasewith shaliness in sand. Purer shales have distinctly higherVP/VSvalues.

VP/VSvalues are about 2.0, dolomite about 1.85. Similarly,Figure 6 shows the correlation ofVP/VSwith dolomite (1.85)and limestone (1.95). Again, as the limestone fraction versusdolomite increases, so do theVP/VSand PEF logs.

General empirical relationships or calibrated rock modelsmay be useful to determineVS if onlyVP or other nonelastic

logs are available (Castagna et al., 1985; Jrstad et al., 1999).P- and S-log values also form the basis for generating syn-

thetic seismograms, which assist in the analysis of P-P and P-Ssections. Lawton and Howell (1992) developed a procedurefor calculating one-dimensional P-S synthetic seismograms (byray tracing through a layered medium with use of Zoeppritzenergy partitioning). Examples of P- and S-velocity logs andtheir corresponding P-P and P-S synthetic seismograms fromthe Blackfoot area of southern Alberta are shown in Figure 7.

We recall that elastic-wave velocities and impedances canbe related to various combinations of the Lame parametersand density. For example, P-wave impedance,IP , can be writ-ten as I2P = (VP)

2 = (+ 2), and S-wave impedance, IS, asI2S = (VS)

2 =, where , and are the Lame parametersand is the density. Goodway et al. (1997) write= I2P 2I

2S,

and suggest that analysis ofand can provide an indica-tion of pore fluids. Other authors (e.g., Duffant et al., 2000)group the terms in equation (1) to define a shear-wave elasticimpedance(SEI).TheSEIvalueis of a generalized impedanceformSEI() = VaS

b, whereaand barefunctions of theP-wave


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1352 Stewart et al.

incidence angle and an average VP/VSvalue. The SEImaybe computed from logs and used to interpret P-S data or guideinversions.

Sonic reflection imaging, using an array-sonic logging tooland processing reflections or diffractions instead of directarrivals, shows considerable promise for reservoir imaging.

Esmersoy et al.(1998)show an example of migratingdatafromSchlumbergersDipole Shear SonicImager in a horizontalwellto create both P- and S-wave sections. They concluded that re-flectors at a range of 3 m were imaged, with the possibility ofimaging up to 10 m.

Vertical seismic profile (VSP) surveys

VSP surveys generally use three-component (3-C) geo-phones and have done so for many years (Toks oz and Stewart,1984; Hindset al.,1996; Hardage, 2000). This is partiallya resultof using offset sources that generate clear P and S energy onboth horizontal and vertical channels (Figure 8). Competentdeeper rocks usually have higher velocities that allow wavesto propagate at large angles from the vertical direction. This

is different from the surface seismic case where the generallylow-velocity near surface bends raypaths to thevertical. At thesurface, this places P-waves largely on the vertical geophoneand S-waves on the horizontal elements. In the VSP case, mul-ticomponent analysis with 3-C recording is usually required todisentangle the P- and S-wave energy on all three channels.

Interestingly, VSP processing has had an impact on P-S sur-face analysis: P-wave reflection points between a given source

FIG. 6. From the left:VP/VS, VLS (volume limestone versus dolomite; greater limestone fraction plots to theright), and PEF (photoelectric logs) plotted in depth for the Davey well (3-13-34-29W4) in central Alberta. Notethe consistent tracking ofVP/VSwith the limestone volume (from Miller, 1996).

FIG. 7. From theleft:P-wave impedancelog,P-P syntheticseis-mogram, S-wave impedance log, and corresponding P-S syn-thetic seismogram for the 08-08-23-23W4 well in the Blackfootfield, southern Alberta (from Stewart et al., 1996). The P-wavesynthetic seismogram uses a 8-12-75-85-Hz Ormsby wavelet;the S-wave seismogram has a 8-12-45-55-Hz Ormsby wavelet.


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and a specific VSP receiver at different depths form a curvedtrajectory in depth; they do not fall on a straight common-midpoint line (Figure 9a). Note that the location of P-S re-flection points in the VSP geometry are also curved and dis-placed toward the receivers (Figure 9b). Such is also the casewith the P-to-S conversion for a surface source and receiver

(Figure 3). The VSP case helped researchers understand howto do common-conversion-point (CCP) mapping for P-S datain a surface geometry.

A basicaim ofthe VSPsurveyisto determineseismicintervalvelocities. From the traveltimes of first-break energy in depth,we can calculate velocities. An example from the Hamburgarea of central Alberta (Coulombe et al., 1996) is shown inFigure 10.Wenote thelowVP/VSvalueof theporous dolomitewith respect to the surrounding limestones. In addition, theseismic velocities are generally lower than sonic values as wewould expect from attenuation-dispersion arguments.

We can also assemble well logs, VSP data, synthetic seismo-grams, and surface seismic into a compelling display called acomposite plot orL plot. This is a very useful compendium ofcorrelated data that often allows a more confident interpreta-

tion. An example is the composite plot from the Rolling Hillsof southern Alberta shown in Figure 11 (Geis et al., 1990).Note the good correlation of events across the various datatypes. Throughout the recording and processing sequence, it iscritical to keep polarities consistent. This can be accomplished

FIG.8. VSP geometry with an offset source. Both transmittedand reflected P-P and P-S waves are shown.

FIG.9. Schematic diagram of (a) P-P reflection trajectories and (b) P-S conversion points for the VSP case of a surface source andsubsurface receivers. The midpoint (MP) and asymptotic conversion point (ACP) for a surface source are indicated.

by using SEG recommended field polarities and the Aki andRichards (1980) energy-partitioning equations. When we dothis, a particular reflector will generally show the same polar-ity on P-P and P-S field data in the normal case whereVP ,VSand all change in the same direction (Brown et al., 2002).

Close to the point of reflection (in depth), P-S and P-P

events have about the same frequency content (Figure 12),implying that P-S images should have higher spatial resolutionthan the associated P-P sections. In fact, this is often observedin VSP images. In the shallow surface-seismic case, P-Sresolution may also be superior to that of the P-P data.However, the opposite is generally true for the deeper section.Unfortunately, by t he time the deeper P-S events are recordedat the surface, their frequency content has often decreased rel-ative to that of the P-wave (Figure 13). Greater attenuation oftheshorter P-Swavelengths is likelya major contributor to thisloss. Deffenbaugh et al. (2000) indicate that for cases whereQP> Q S, there is a resolution crossover depth below whichthe P-P mode gives better resolution than t he P-S. IfQ S>QP ,then P-S resolution should be better than the P-P case. How-ever, other factors, such as large variation in the stratigraphy

of the shallow section (with attendant changes in velocity,impedance, anisotropy, and attenuation) may complicateS-wave propagation and lead to a decrease in its bandwidth.

Another example of P-P and P-S VSP data comes from theWillesden Green region of central Alberta (Figure 14). We seemuch more reflection activity in the shallow part of the P-Ssection as compared to the P-P section (Stewart et al., 1995).In addition to the higher spatial resolution of P-S events mea-sured in situ, this may be the result of larger relative changesin S-wave impedance relative to the P-wave impedance. In thiscase, both sections have been plotted in P-wave time (effec-tively, both sections areprocessed to depth andthen convertedback to P-wave time).

Coulombe et al. (1996) used VSP measurements to ana-lyze AVO effects in a carbonate section. They found that P-P

and P-S AVO effects were in evidence and could be modeled(Figures 15 and 16). In the VSP data, the P-S section gavea higher resolution picture in which the top and bottom ofthe porous zone could be identified. Daures et al. (1999) use3-C VSP data to guide the processing and interpretation ofa four-component (4-C) ocean-bottom seismic (OBS) datasetfrom the Balder field, North Sea. They found P and S ve-locities from the VSP to be useful in calibrating sonic logs,


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FIG. 10. Interval velocity from VSP and blocked sonic logs. The porous dolomite reservoir shows a significantVP/VSdroprelativeto surrounding limestones(from Coulombe et al., 1996). Theseismic velocitiesare somewhatlower than the sonic values.

FIG. 11. Composite plot showing well logs, VSP in depth and two-way time, synthetic seismograms, P-wave surface seismic, andVSP sections. Data are from southern Alberta. Note the great reflection activity (and noise) in the converted-wave section (fromGeis et al., 1990). The P-P and P-S VSP extracted traces or corridor stacks are labeledP-VET andPS-VET, respectively.


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FIG. 12. Spectra from the P-wave VSP and P-S VSP data ofFigure 11. The similar temporal frequency content of P- andS-wave data, averaged over depths from 520 m to 1840 m, indi-cates a higher spatial resolution of the S-wave data (from Geiset al., 1990).

FIG.13. Frequency coherency spectra from the Carrot Creek,Alberta, surveys for (a) P-P data and (b) P-S data. Fromthe depth of interest, the P-P and P-S dominant frequenciesrecorded at surface are32 and21 Hz, respectively(from Eatonet al., 1991).

gatheringtheOBSdata,andprocessingit.Inaddition,theVSP-extractedtraces (VETs)for P-Pand P-Swaves were importantassets in correlating the various seismic sections. Leaney et al.(1999) use multioffset VSP data to build elastic (and anelas-tic) models for converted-wave simulations. They found thatit was important to take anisotropy and attenuation into ac-

count when attempting to produce realistic converted-waveseismograms.

Multicomponent surface-seismic acquisition

An early discussion concerning the surveying, analysis, andinterpretation of converted waves was published by Garottaet al. (1985). They useda two-element (verticaland horizontal)geophone for acquisition. The data recorded were quite good.Nevertheless, using a 3-C geophone is now recommended sothat off-line effects, misorientation, anisotropy, crooked lines,and 3-D shooting can be handled.

Lawton and Bertram (1993) tested four 3-C geophones, us-ing a source at various azimuths to the receivers. The goal ofthis survey was to determine if the output response (particle

motion plot or hodogram) of the horizontal elements wouldindicate the direction of the source from the receiver. That is,would the geophone response faithfully reproduce anticipatedparticle motion polarization? They found that the three geo-phones commercially available at that time all performed well.This was important for further establishing the vector fidelityof the field measurements before proceeding to more sophis-ticated processing. Guevara (2000) conducted similar analysisfor thepolarizationof two-dimensional, three-component(2D-3C) data recorded from an offline source in Blackfoot field,Alberta. In this case too, the azimuths of the data hodogramscompared well to those of the source-receiver field geometry.Especially useful were the azimuths determined from refract-ing S-waves and ground roll.

Eaton and Lawton (1992) analyzed the fold of a 2-D P-S

section and found it to be oscillatory under certain conditions.Careful design is requiredto avoid regions of lowfold. Vermeer(1999) and Lawton and Hoffe (2000) also discuss issues in thedesign of 3-D surveys, including the raypath asymmetry anddepth-targeted techniques. The raypath asymmetry will pushreflection points toward the receiver lines giving different cov-erage from that expected from P-wave data (Ronen et al.,1999). Staggering receiver lines (or shooting slightly off theorthogonal) can smooth P-S fold. Shooting on the half-stationmay also help fold distributions. In 3-D surveys, there may besomeoperational and processingadvantages to shooting paral-lelto thereceiverlinesinsteadof orthogonal to them.However,subsequent analysis methods that rely on a wide range of az-imuths (e.g., azimuthal anisotropy determination) would nor-mally require some kind of crossline shooting (Rosland et al.,1999). Processes such as adjacent-trace averaging, depth- andvelocity-variant binning, and dip moveout (DMO) will aid insmoothing the final fold.

Acquisition limitations

The recording of land and marine multicomponent datais still somewhat constrained by several factors. Three-component geophones and 4-C cables have sometimes beenin short supply. As demand continues to increase, more


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FIG. 14. P-S and P-P VSP sections from the Willesden Green surveys (Stewart et al., 1995). Note the greaterreflectionactivityin the P-Ssection in the shallow regions. Bothsectionsare plotted in two-way P-wave traveltime.

FIG.15. AVO traces for VSP data. The P-wave and S-wave gathers are from offsets ranging from 80 m to 2500m (from Coulombe et al., 1996).


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multicomponent sensors are being built. Several types of au-toleveling surface geophones (mechanical and solid-state) arecurrently being deployed which promise to increase plantingefficiency and fidelity.

There are still issues about the use of arrays or single phonesthat need to be resolved with careful field work and process-

ing. However, several tests on land indicate that by the finalmigrated-section stage, there is little difference in P-wave datafrom a single vertical element of the 3-C geophone and con-ventionalvertical-elementarrays. Thereis evidencethat 3-C ar-rays mayactuallydamage theP-S data dueto large andrapidlyvarying S-wave (receiver) statics (Hoffeet al., 2002). Poddedgeophones or receivers clustered in a radius of about 1 m mayprovide signal-to-noise ratio enhancements without the asso-ciated static degradation.

Buried geophones are sometimes said to record a bettersignal with less noise. We have often used 3-C geophones inaugered holes about 0.3 m deep to minimize wind-noise ef-fects, freezing/thawing conditions, and other cultural noise. Totest theeffectof a deeperplant, we analyzed two test lines with3-Cgeophones buriedup to depthsof 18 m. Somewhat surpris-

ing to us, we have not found an improvement in data quality(Cieslewicz, 1999). This may be a consequence of factors suchas difficulty in obtaining a good 3-C geophone plant at the bot-tom of a drilled hole, near-surface multipathing, and the lossof signal amplification otherwise realized on the free surface.

Other solutions being sought in P-S data acquisition includethe source type and parameters to be used for optimal gener-ation of converted waves and the overall design of recordingboxes, telemetries,and dataharvesting.The costof a multicom-ponent survey continues to be an issue, but more experiencedcrews and plentiful equipment are helping to improve dataquality while lowering costs.

Marine 4-Cequipment andprocedures arerapidlyadvancingas well. Topics of current attention include seafloor geophone

FIG.16. AVO traces for VSP data. The P-wave (a) modeled synthetic and (b) field data show AVO effects, as dothe P-S data [(c) synthetic and (d) field]. The gathers are from source offsets ranging from 80 m to 2500 m (fromCoulombe et al., 1996). The top and bottom of the interpreted porous dolomite layer are indicated. Note thatthere are some character differences among the various P-P and P-S data.

coupling, vector fidelity (Tree, 1999), the effects of geophonegimbaling, and receiver statics. For 3-D P-S wave data, shearwaves can be polarized in any direction, and it is thereforeimportant that the earth response of the two horizontal geo-phones be identical. When their response differs, data fromthe components can not be combined optimally in a vector

sense for 3-D processing. Gaiser (1998) extended the con-cept of surface consistency to multicomponent receivers tocorrect for differences in geophone coupling between inlineand crossline detectors from ocean-bottom cable (OBC) data.Vector deconvolution operators are designed by minimizingtransverse energy, and are applied to crossline and vertical-component data, resulting in multicomponent spectra that arewell balanced. Figure 17 shows an example of portions of twocrossline receiver gathers before and after compensation. Itillustrates how undesirable 8-Hz resonance (Figure 17a) canbe attenuated and the bandwidth of P-S reflections improved(Figure 17c). Correctingfor variations in couplingimprovesthecrossline and inline components for 3-D vector processing andmakes the crossline response more consistent for all receivergathers.

P-S data processing

As shown in Figure 1, the reflected S-wave returns tothe surface more vertically than the incident P-wave. Thus,the reflection or conversion point is not midway between thesource and receiver. Furthermore, this conversion point lo-cation moves toward the receiver for shallower reflectionsand largerVP/VSvalues (Figure 3). Several authors have pre-sented analysis of the asymmetric reflection-point trajectory(Chung and Corrigan, 1985; Tessmer and Behle, 1988) and itsimportance in P-S imaging. Garotta (1985) and Frasier andWinterstein (1990) outline procedures for handling P-S data.Stewart (1991) extended Chung and Corrigans (1985) work to


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describe converted waves where the source and receiver hadunequal elevations.

Garotta et al. (1985), in an early and insightful paper, pro-cessed P-P and P-S data by handling vertical and horizontalchannels separately with different statics and velocities. Theyalso introduced the concept of what was later called asymp-

totic binning. In asymptotic binning, the whole trace is put atthe location definedby a reflector depth that is large comparedto thesource-receiver offset. For a single-layercase, this wouldbeXa = X/(1 + VP/VS), whereXais the conversionpoint offsetfrom the receiver position andXis the source-receiver offset.Thomsen (1999) showed how an equation of this form couldalso be used for the case of vertical transverse isotropy (VTI).Usingone conversionpoint location allows gatheringfor veloc-ity analysis andavoids thecomplication of trace mapping priorto stack. We note that Garotta (1999) comprehensively revisitsconverted-wave analysis as the 1999 Distinguished Instructorof the Society of Exploration Geophysicists.

Because of the low S velocity in the near surface, receiverstatics in the P-S survey can be large. Lawton (1990) foundreceiver static shifts of about 70 ms for a case in the Alberta

plains. Cary and Eaton (1993) found receiver statics of 100 ms,as did Isaac (1996) in a case from Cold Lake, Alberta. Caryand Couzens (1998) also discussed the problems in separatingthe effects of structure from those of statics in a 4-C case fromthe Mahogany field, Gulf of Mexico. Clearly, the near surfacehas a marked influence on P-S data as a result of these largeand variable statics, but it also has another undesirable effect:attenuation. This remains a limitation of surface P-S analysis.Further work on Q filtering will undoubtedly help.

Separation of P and S events on the full 3-C record hasbeen approached using various techniques. In VSP analysis,methods based on Dankbaars (1985) scheme of polarization

FIG. 17. Crossline responses from portions of two different 3-D common-receiver gathers before compensation (a, b) and aftercompensation (c, d). Gather (a) is an example of a poorly coupled receiver exhibiting 8-Hz resonance, and gather (b) is an examplefrom a receiver of average coupling. After correction, the two receiver gathers are more consistent in their frequency content,indicated by bandwidth and by relative amplitudes of reflections and sediment-water interface waves (Gaiser, 1998).

analysis and f-kfiltering have proven useful. In the marineenvironment, the responses of ocean-bottom receivers are an-alyzed using formulations based on a fluid-solid interface (e.g.,Donati and Stewart, 1996). Other work using 3-C array form-ing to reduce noise as well as to estimate direction and wavetype looks promising. Yuan et al. (1998) showed some excel-

lent 4-C data from the North Sea, where they concluded thatthe P-S sections were of better quality than the P-P sections.They used a match-filter approach to remove P-S reflectionsfrom the vertical geophone data.

In transmission through an azimuthally anisotropic mate-rial, shear waves generally split into fast and slow polariza-tions. Thus, two polarized converted waves (P-S1and P-S2, fastand slow, respectively) arrive at the receiver. These potentiallysuperposed events need to be separated. There are various al-gorithms for doing this (e.g., Alford, 1986; Harrison, 1992) thatrely on searching for two similar events projected onto a newset of rotated horizontal channels that are time delayed andorthogonally polarized. Lou et al. (2000) scan through a se-ries of rotation angles and time delays in 4-C data from theValhall field, North Sea, to estimate the S1 and S2 directions

and anisotropy magnitude. They find P-S1andP-S2time delaysof about 30 ms at the target level and an anisotropy directionconsistent with other seismic and well data.

Slotboom (1990) considered the velocity analysis problem.He derived a shifted hyperbola equation for NMO correc-tion that can correct the offset traveltimes more accuratelythan a normal hyperbolic velocity analysis. Including a fourth-order term in the moveout equation can be helpful. Stewartand Ferguson (1996) presented a method to find an S-waveinterval velocity from P-S stacking velocities using the Dixassumption that the stacking velocity is equal to the rmsvelocity.


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After NMO, it is important to understand the Fresnel zone(or the averaging aperture in a stacked section) and the po-tential of P-S data to be migrated. Eaton et al. (1991) derivedthe P-S Fresnel zone and found that, for the same frequencies,the P-S Fresnel radius is smaller than the corresponding P-Pcase. However, with the lower P-S frequencies often observed

at the surface, P-P and P-S radii work out to be about thesame. They also showed that P-S data could be migrated afterstack in a kinematic (traveltime) sense. Harrison and Stewart(1993) considered the migration problem further and deriveda P-Smigration velocity fora horizontallylayeredmaterial. Aswith P-waves, P-Sreflectionsare shifted in regions of dip. Thus,someprocedures must be undertakenin the stacking process toput reflections at their correct zero-offset positions. Harrison(1992) developed an equation and procedure for the DMOcorrection of converted-wave data.

Several authors haveinvestigatedmethods to enhance imag-ingvia prestack time migrationin isotropic(e.g. Nicoletis et al.,1998) and anisotropic (e.g., Riste and Fjellanger, 2000) materi-als. Depth migration of P-Sdata canbe accomplished(Kendallet al., 1998; Hoffe and Lines, 1999), which, in addition to pos-

sibly better imaging, creates P-P and P-S sections sharing thesame depth axis (as opposed to raw P-P and P-S time axes).The use of positive and negative source-receiver offsets canhelp with improved velocity analysis and imaging (Dai et al.,2000). Van Doket al. (1997) outline a 3C-3Dprocessingflow fordata acquired in the Wind River Basin, Wyoming. Key stepsin their sequence are full P-P processing of the vertical geo-phone data (especially for source statics and velocities to beused with theP-S data),editsof thehorizontal components, co-herent noisefiltering, surface-consistent statics, deconvolution,CCP binning, Alford rotation, anisotropic layer stripping, P-SNMO, stack, and 3-D f-kmigration. With respect to S-wavebirefringence (splitting), Gaiser et al. (1997) note that thereis considerably more room in P-S analysis for enhancement ofthedata andassessmentof fracturesand stressstate. Zhuet al.,

(1999) emphasize the need for careful preprocessing of mul-ticomponent data and the importance of the velocity fields tothe final prestack imaging.

Continuing with the analysis of our reflectivity section, wemay be interested in extracting an estimate of actual rockproperties (e.g., impedance, velocity). Stewart (1991) deriveda method for converting S-wave reflectivity to a shear-velocitylog. This method is similar to seismic inversion via the Seislogmethod, where we basically integrate and exponentiate theseismic trace to provide an estimateof thevelocity. Valencianoand Michelena (2000) used a small-offset approximation toequation (1) to develop an inversion procedure for stackedP-S data. Jin et al. (2000) applied an AVO inversion techniqueto an OBS data set from the North Sea. They illustrated thepractical use of AVO inversion for S-wave velocity and densityfor seismic reservoir characterization; in particular, for fluidcontact detection and pore fluid change.

Interpretation techniques

P-S data can be interpreted on their own, but generally willbe analyzed in conjunction with P-wave sections or volumes.Thus, a primary aspect of interpretation is correlating the P-Pand P-S events. There are a number of ways to accomplish this.As indicated earlier, Lawton and Howell (1992) developed a

P-S synthetic seismogram program to assist in the correlationprocess. This modeling algorithmuses the offset-dependentre-flectivityand ray-traced traveltimes of both P-Pand P-Seventsto create synthetic seismograms. We need an acoustic velocityfor this modeling, but can infer or guess densities and S-wavevelocities if they are not otherwise available. These resultant

seismograms are, in fact, AVO stacks of offset reflectivities.Classically, the zero-offset P-S reflection coefficient is zero, butthe zero-offset P-S section obviously does not attempt to pro-vide this. Rather, the final P-S stack to zero-offset traveltimegives an average of the offset-dependent P-S reflectivities.

We canalter theVP/VSvaluein theP-S syntheticseismogramto refine the correlation. So, in practice, we tie the P-wave syn-theticseismogramto theP-Psection,the P-PandP-S syntheticstogether, and the P-S synthetic seismogram to the P-S section.Chan (1998)suggested plotting theP-P andP-S sections in log-arithmic time; that is, displaying the sections as lntPP and lntPS, wheretPP and tPSare the P-P and P-S two-way reflectiontimes, respectively. For a nearly constantVP/VSvalue, just abulk shift can then assist in tying the sections. Even using asingleVP/VSvalue for shrinking the P-S time scale in a plot

can often provide a general correlation to the P-P section.These correlations orVP/VSvalues canbe used to determine

a mapping between tPS andtPP for time conversions. Gaiser(1996) developed a robust multicomponent correlation analy-sis to obtain average and interval VP/VSvalues. However ac-complished, sections or volumes must ultimately be plotted onthe same scale (whether it is P-wave time or depth) to providean understandingof the subsurface. Migrationto depthwithVPandVSvelocity fields is certainlya goal for many final analyses.

Time-structure sections and isochrons are used in P-S inter-pretation similarly to P-P techniques. However, we can alsotake the ratio of P-P and P-S isochrons from the same inter-preted horizons to generateVP/VSvalues. In this case,VP/VS=2(TPS/TPP) 1, whereTPSand TPPare the corresponding P-Sand P-P isochrons. Miller (1996) shows a case of this isochron-

ratio analysis from Lousana field, Alberta (Figure 18).Larson (1996) and Margrave et al. (1998) develop interpre-tation techniques for the analysis of 3-D multicomponent vol-umes.Time slices, horizon andisochronmaps, andcoupled P-PandP-S results canall be useful. One3C-3D seismic surveycanprovide three products: the P-P volume and the anisotropicvolumes (P-S1 and P-S2, where S1 is the fast S-wave and S2the slow S-wave). Thus, there are a number of new, indepen-dent sections to compare, contrast, and integrate. Althoughthis presents some wonderful interpretation opportunities, itcan also be difficult and time-consuming, as Rutledal et al.(2000) indicate in their interpretation of 4C-3D data from theOseberg field, North Sea.

WHATS LEFT TO DO?

Converted-wave exploration has come a long way in the lastseveral years, but there is still plenty of room left for progress.Determining which recording environments allow acquisitionof good P-Sdataand howto carry outthat acquisition areareasfor further effort. For example, what vibrator sweep parame-ters will provide the best P-S data has not yet been the subjectof much experimentation. In addition, finding an appropriatebalance between capturing high-quality P-wave data as well asP-S data challenges our survey design expertise.


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1360 Stewart et al.

Muchremainsto be donein designingmarinesurveys, ocean-bottom recording systems, and the deployment of equipment.Both cables and discrete nodes have advantages and disadvan-tages. Somenovel acquisition techniqueshave beenattempted.Moldoveanu et al. (1998) indicate that in transition zones P-Sdata can be acquired by ramming 4-C receivers into the mud.

Stewart et al. (2001) deployed a five-level, three-componentVSP tool in a shallow lake and winched it across the lakebottom to acquire data from an onshore vibrator. They foundthat credible P-P and P-S sections could be constructed from

FIG. 18. P-P section (top) and P-S section (middle) from Lousana field, Alberta. TheVP/VSvalue (bottom) isextracted from the interpreted P-P and P-S sections. The lower values in the Paleozoic, from about shot points190 to 215, are coincident with an underlying oil-bearing reef (Miller, 1996).

the recorded data. New solid-state, digital geophones [andnewer optical motion sensors (see Bostick 2000)] with threeand four components promise broader band recordings. Be-ing able to record high-fidelity data down to the 1-Hz rangeopensup exciting possibilities for better wavelet definition andmore complete inversions, especially in the converted-wave

case.Investigatingother modes in multicomponentdata willallow

us to separate undesirable from desirable modes as well as tomake other sections. In some cases, a vertical vibrator mayalso


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generate enough S-wave energy to allow an S-S or S-P sectionto be created directly. And, of course, if the signal is there weshould try to use it. Fyfe et al. (1993) show a case from SaudiArabia in which P-S and S-S sections were produced from avertical vibrator source recorded into 3-C geophones.

Furthermore, an S-S section may be produced from dyna-

mite data. Nieuwland et al. (1994) give an example of process-ing a pS-S survey in The Netherlands. In this case, an upgo-ing P-wave from the dynamite source converts at the surfaceto a downgoing S-wave that is reflected back to the surfacefrom various layers as an S-wave. Credible S-wave sectionsare produced, along with their P-wave counterparts, and areinterpreted for gas effects. A downgoing shear conversion atthe ocean floor and its reflection (PS-S) may be extractablefrom marine 4-C data in some cases (although anecdotallythis seems rare). Nonetheless, Tatham and Goolsbee (1984)describe a case of the PS-SP event (the upcoming S-wave con-verting toa P-wave atthe oceanbottom) from offshorewesternFlorida. There is promise that the base of high-velocity layers(HVL) can be imaged using mode-converted S-waves by re-placing the P-wave velocity in the HVL with an appropriate

S-wave velocity (Purnell, 1992). Additionally, Hanssen et al.(2000) suggest that whilelocally converted modes are too weakfor subbasalt (HVL) imaging, the simple P-S mode may beuseful.

More sophisticated processing techniques will be useful toresolve statics, identify and use anisotropy, estimate veloc-ities, and perform more accurate migrations (especially infaulted and folded areas). We also need to understand a greatdeal more about how the near-surface damages S-wave data.Improvements to interpretation methods incorporating vec-tor and multimode concepts (Mueller et al., 1999) will bebeneficial.

As we develop more confidence in P-S images, it is becom-ing useful to repeat the 3-D multicomponent survey to al-low the possibility of time-lapse (4-D) imaging. In this case,

we are looking for the seismic signature of fluid change andmovementa very economic, but complicated quest. As thepressure and saturation state of the reservoir is altered in thecourse of hydrocarbon production,the elastic (as well as acous-tic) properties of the rock change, demonstrating the ultimateneedfor full (3C-4D or 4C-4D) multicomponent recording andanalysis.

CONCLUSIONS

The reflection seismic method has used P-waves for manyyearsand with great success. However, there is more tobe done in exploration seismology (especially with regard tolithology and fluids) by using the other elastic modes that arepart of the seismic survey, particularly the P-S converted wave.

P-S seismic exploration has been developing for about20 years.The basictools of P-S analysis include drill-coreevalu-ation, shear-sonic logs, 3-C VSP, elastic synthetic seismograms,and of course multicomponent land and marine seismic sur-veys. Many of the fundamental techniques for handling thesedata have been established. There are currently a number ofcompanies providing multicomponent seismic services and re-search groups attempting to further develop the method. Re-cent examples of successful P-S imaging indicate a maturing ofthe technology.

ACKNOWLEDGMENTS

We express our deep appreciation to the sponsors of theCREWES Project for their commitment to the developmentof multicomponent seismology. Many thanks to the CREWESstaff, especially former employees Joanie Whittemore and

Chuandong (Richard) Xu, for their help in assembling thispaper. This paper benefited considerably from the insightfulreview by Dr. Mike Mueller of BP. We thank him, the otherreviewers, and 20 students in a recent graduate course onConverted-wave Seismic Exploration at the University of Cal-gary for the generous gift of their comments. This work wasfurther supported by a collaborative research grant from theNatural Sciencesand Engineering ResearchCouncilof Canada(CRD #223726-99).

REFERENCES

Aki, K., and Richards, P. G., 1980, Quantitative seismology: Theoryand methods: W. H. Freeman and Sons.

Alford,R.M.,1986,Sheardatainthepresenceofazimuthalanisotropy:Dilly, Texas: 56th Ann. Internat. Mtg., Soc. Expl. Geophys.,Expanded Abstracts, 476479.

Arnold, A., and Chiburis, E., 1998, AVOCurrent status and thefuture: 68th Ann. Internat. Mtg., Soc. Expl. Geophys., ExpandedAbstracts, 248250.

Bostick III, F. X., 2000, Field experimental results of three-componentfiber-optic seismic sensors: 70th Ann. Internat. Mtg., Soc. Expl.Geophys., Expanded Abstracts, 2124.

Brown, R. J., Stewart, R. R., and Lawton, D. C., 2002, A proposedpolarity standard for multicomponent seismic data: Geophysics, 67,10281037.

Caldwell, J., 1999, Marine multicomponent seismology: The LeadingEdge,18, 12741282.

Cary, P. W., and Couzens, R. A., 1998, Processing 4-C data fromMahogany field, Gulf of Mexico: CREWES Research Report, 10,29.129.25.

Cary, P. W., and Eaton, D. W. S., 1993, A simple method for resolvinglarge converted-wave (P-SV) statics: Geophysics, 58, 429433.

Castagna, J. P., Batzle, M. L., and Eastwood, R. L., 1985, Relationshipsbetween compressional-wave and shear-wave velocities in clasticsilicate rocks: Geophysics,50, 571581.

Chan, W. K., 1998, Analyzing converted-wave seismic data: Statics,interpolation, imaging, and P-P correlation: Ph.D. thesis, Univ. ofCalgary.

Chung,W. Y.,and Corrigan,D.,1985, Gatheringmode-converted shearwaves:A modelstudy:55th Ann., Internat.Mtg. Soc.Expl.Geophys.,Expanded Abstracts, 602604.

Cieslewicz, D., 1999, Near-surface characterization using three-component buried geophones: M.Sc. thesis, Univ. of Calgary.

Clark, D., 2000, Whither geophysical technology? The views of thevendors: The Leading Edge,19, 862873.

Coulombe, C. A., Stewart, R. R., and Jones, M. E., 1996, AVO pro-cessing and interpretation of VSP data: Can. J. Expl. Geophys., 32,4162.

Dai, H., Li, X.-Y., and Mueller, M. C., 2000, Compensating for the ef-fects of gas clouds by prestack migration: A case study from Valhall:70th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts,10471050.

Dankbaar, J. W. M., 1985, Separation of P- and S-waves: Geophys.Prosp.,33, 970986.

Daures, R., Granger, P.-Y., Vuillermoz, C.,1999, 4C OBS data process-ing guided by well data, Balder field case history: Presented at the61st Ann. Conf., Eur. Assn. Geosci. Eng.

Deffenbaugh,M., Shatilo, A.,Schneider,B., and Zhang, M., 2000,Res-

olution of converted wavesin attenuatingmedia: 70thAnn. Internat.Mtg., Soc. Expl. Geophys., Expanded Abstracts, 11781180.Donati, M. S., and Stewart, R. R., 1996, P- and S-wave separation at a

liquid-solid interface: J. Seis. Explor.,5, 113127.Duey, R.,2001, Multicomponent acquisition:Fromside dishto entree?:

Harts E&P,74, no. 1, 6870.Duffant, K., Landr, M., and Rogn, H., and Al-Najjar, N. F.,

2000, Shear-wave elastic impedance: The Leading Edge, 19, 12221229.

Eaton, D. W. S., and Lawton, D. C., 1992, P-SV stacking charts andbinning periodicity: Geophysics,57, 745748.

Eaton, D. W. S., Stewart, R. R., and Harrison, M. P., 1991, The Fresnelzone for P-SV waves: Geophysics, 56, 360364.


15/16

1362 Stewart et al.

Esmersoy, C.,Chang,C., Kane, M.,Coates,R., Tichelaar, B., and Quint,E., 1998, Acoustic imaging of reservoir structure from a horizontalwell: The Leading Edge,17, 940946.

Frasier, C., and Winterstein, D., 1990, Analysis of conventional andconverted mode reflections at Putah Sink, California using three-component data: Geophysics,55, 646659.

Fyfe, D. J., Dent, B. E., Kelamis, P. B., Al-Mashouq, K. H., andNietupski, D. A., 1993, Three-component seismic experiments in

Saudi Arabia: Presented at the 55th Ann. Mtg., Eur. Assn. Expl.Geophys.Gaiser, J. E., Fowler, P. J., and Jackson, A. R., 1997, Challenges for

3-D converted-wave processing:67th Ann.Internat.Mtg., Soc.Expl.Geophys., Expanded Abstracts, 11991202.

Gaiser, J. E., 1996, Multicomponent VP/VS correlation analysis:Geophysics,61, 11371149.

1998, CompensatingOBC data forvariations in geophone cou-pling: 68th Ann. Internat. Mtg., Soc. Expl. Geophys., ExpandedAbstracts, 14291432.

Garotta, R., 1985, Observation of shear waves and correlation with Pevents, inDohr,G.P., Ed.,Seismicshear waves:Part B: Applications:Geophysical Press, 186.

1999, Shear waves from acquisition to interpretation: Soc. Ex-plor. Geophys.

Garotta, R., Marechal, P., and Magesan, M., 1985, Two-component ac-quisitionasaroutineprocedureforrecordingP-wavesandconvertedwaves: Can. J. Expl. Geophys.,21, 4053.

Geis, W. T., Stewart, R. R., Jones, M. J., and Katopodis, P. E., 1990,Processing,correlating,and interpretingconverted shearwaves fromborehole data in southern Alberta: Geophysics, 55, 660669.

Goodway, W., Chen, T., and Downton, J., 1997, Improved AVO fluiddetection and lithology discrimination using Lame petrophysicalparameters: , , and / fluid stack, from P and S inversions:Presented at the Ann. Nat. Mtg., Can. Soc. Expl. Geophys.

Gu eguen, Y., and Palciauskas, V., 1994, Introduction to the physics ofrocks: Princeton Univ. Press.

Guevara, S. E., 2000, Analysis and filtering of near-surface effects inland multicomponent seismic data: M.Sc. thesis, Univ. of Calgary.

Hanssen, P., Li, X.-Y., and Ziolkowski, A., 2000, Converted waves forsub-basalt imaging?: 70th Ann. Internat. Mtg., Soc. Expl. Geophys.,Expanded Abstracts, 11741177.

Hardage, B. A., 2000, Vertical seismic profiling: Principles, 3rd ed.:Elsevier.

Harrison, M. P., 1992, Processing of P-SV surface-seismic data:Anisotropyanalysis, dip moveout, and migration:Ph. D.thesis, Univ.of Calgary.

Harrison,M. P.,and Stewart, R. R.,1993,Post-stackmigrationof P-SVseismic data: Geophysics,58, 11271135.

Hinds, R. C., Anderson, N. L., and Kuzmiski, R. D., 1996, VSP inter-pretive processing: Theory and practice: Soc. Explor. Geophys.

Hoffe, B. H., and Lines, L. R., 1999, Depth imaging by elastic waves

Where P meets S: The Leading Edge, 18, 370372.Hoffe, B. H., Margrave, G. F., Stewart, R. R., Foltinek, D. S., Bland,

H. C., and Manning, P. M., 2002, Analyzing the effectiveness of re-ceiver arrays for multicomponent seismic exploration: Geophysics,67, in press.

Isaac, J. H., 1996, Seismic methods for heavy oil reservoir monitoring:Ph.D. thesis, Univ. of Calgary.

Jin, S., Cambois, G., and Vuillermoz, C., 2000, Shear-wave velocity anddensity estimation from PS-wave AVO analysis: application to anOBS dataset from the North Sea: Geophysics, 65, 14461454.

Jrstad, A.,Mukerji,T.,and Mavko, G., 1999,Model-based shear-wavevelocity estimation versus empirical regressions: Geophys. Prosp.,47, 785797.

Kendall, R. R., and Davis, T. L., 1996, The cost of acquiring shearwaves: The Leading Edge, 15, 943949.

Kendall, R. R., Gray, S. H., and Murphy, G. E., 1998, Subsalt imag-ing using prestack depth migration of converted waves: MahoganyField, Gulfof Mexico: 68thAnn. Internat. Mtg., Soc.Expl. Geophys.,Expanded Abstracts, 20522055.

King, M. S., Marsden, J. R., and Dennis, J. W., 2000, Biot dispersion forP- and S-wave velocities in partially and fully saturated sandstones:Geophys. Prosp.,48, 10751089.

Larson, G. A., 1996, Acquisition, processing, and interpretation of P-Pand P-S 3-D seismic data: M.Sc. thesis, Univ. of Calgary.

Lawton, D. C., 1990, A 9-component refraction seismic experiment:Can. J. Expl. Geophys.,26, 716.

Lawton, D. C., and Bertram, M. B., 1993, Field tests of 3-componentgeophones: Can. J. Expl. Geophys.,29, 125131.

Lawton, D. C., and Hoffe, B. H., 2000, Some binning issues for 4C-3DOBC survey design: 70th Ann. Internat. Mtg., Soc. Expl. Geophys.,Expanded Abstracts, 1720.

Lawton, D. C., and Howell, C. T., 1992, P-SV and P-P synthetic stacks:62ndAnn. Internat. Mtg., Soc.Expl. Geophys., Expanded Abstracts,

13441347.Leaney, S., Cao,D.,and Tcherkashnev, S., 1999,Calibratinganisotropic,

anelastic models for converted-wave simulation: 61st Ann. Conf.,Europ. Assn. Geosci. Eng., Extended Abstracts, 652.

Lou, M., Zhang, Y., and Pham, L. D., 2000, Shear-wave splitting andits implied fracture orientation analysis from PS waves in marinemulti-component seismic data: First Break, 18, No. 12, viiix.

Margrave, G. F., Lawton, D. C., and Stewart, R. R., 1998, Interpreting

channel sands with 3C-3D seismic data: The Leading Edge,17, 509513.Mari, J. L., Coppens, F., Gavin, P., and Wicquart, E., 1994, Full wave-

form acoustic data processing: Editions Technip.Mavko, G., Mukerji, T., and Dvorkin, J., 1998, The rock physics hand-

book: Tools for seismic analysis in porous media: Cambridge Univ.Press.

Miller, S. L. M., 1996, Multicomponent seismic data interpretation:M.Sc. thesis, Univ. of Calgary.

Miller, S.L. M.,and Stewart,R. R.,1990,Theeffectof lithology, poros-ity and shaliness on P- and S-wave velocities from sonic logs: Can J.Expl. Geophys.,26, 94103.

Moldoveanu, N., Rink, U., and Van Baaren, P., 1998, Multicomponentacquisition in transition zone environment: An experimental study:68th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts,738739.

Mueller, M. C., Boyd, A. J., and Esmersoy, C., 1994, Case studies ofthe dipole shear anisotropy log: 64th Ann. Internat. Mtg., Soc. Expl.Geophys., Expanded Abstracts, 11431146.

Mueller, M. C., Barkved, O. I., and Thomsen, L. A., 1999, A strategyfor vector interpretation of multicomponent ocean bottom seismic

data: 61st Ann. Conf., Eur. Assn. Geosci. Eng., poster P067.Nicoletis, L., Svay-Lucas, J., and Prigent, H., 1998, True amplitude

prestack imaging of converted waves: 68th Ann. Internat. Mtg., Soc.Expl. Geophys., Expanded Abstracts, 734737.

Nieuwland, F., Marschall, R., Papaterpos, M., and Sharp, D., 1994, Anexample of the use of shear waves in seismic exploration: J. Seis.Explor.,3, 520.

Purnell, G. W., 1992, Imaging beneath a high-velocity layer using con-verted waves: Geophysics,57, 14441452.

Rider, M., 1996, The geological interpretation of well logs, 2nd ed.:Whittles Publishing.

Riste, P., and Fjellanger, J.-P., 2000, Application of 3-D prestack timemigration for converted waves: 70th Ann. Internat. Mtg., Soc. Expl.Geophys., Expanded Abstracts, 11461149.

Rodriguez, C., 2002, Advanced marine seismic methods: Ph.D. thesis,Univ. of Calgary.

Ronen, S., Bagaini, C., Bale, R., Caprioli, P., and Keggin, J., 1999, Cov-erage and illumination of sea bed 4C surveys: 61st Ann. Mtg., Eur.Assn. Geosci. and Eng., Extended Abstracts, 618.

Rosland, B., Tree,E. L.,and Kristiansen,P., 1999,Acquisition of 3D/4COBS data at Valhall: 61st Ann. Mtg., Eur. Assn. Geosci. Eng., Ex-

tended Abstracts, 617.Rutledal,H., Ertresvag,E. T., and Berg,O. E., 2000,Interpretationand

analysis of the 1997 3D multicomponent seismic survey covering apart of the Oseberg field in the North Sea: 70th Ann. Internat. Mtg.,Soc. Expl. Geophys., Expanded Abstracts, 570573.

Schon, J. H., 1998, Physical properties of rocks: Fundamentals andprinciples of petrophysics, 2nd ed.: Pergamon.

Slotboom, R. T., 1990, Converted wave (P-SV) moveout estimation:60th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts,11041106.

Stewart, R. R., 1991, Rapid map and inversion of P-SV waves: Geo-physics,56, 859862.

Stewart, R. R., and Ferguson, R., 1996, Shear-wave interval velocityfrom P-S stacking velocity: Can J. Expl. Geophys.,32, 139142.

Stewart, R. R., Ferguson, R. F., Miller, S. L. M., Gallant, E., andMargrave, G. F., 1996, The Blackfoot seismic experiments: Broad-band, 3C-3D, and 3-D VSP surveys: Can. Soc. Expl. Geophys.Recorder,21, no. 6, 710.

Stewart, R. R., Huddleston, P. D., and Kan, T. K., 1984, Seismic versussonic velocities: A vertical seismic profiling study: Geophysics, 49,11531168.

Stewart, R. R., Lu, H., Bland, H., and Mewhort, L. E., 2001, A lake-bottom cable seismic survey: Acquisition and processing: Can. Soc.Expl. Geophys. Recorder, 8, 3740.

Stewart, R. R., Pye, G., Cary, P. W., and Miller, S. L. M., 1995, Interpre-tation of P-SV seismic data: Willesden Green, Alberta: CREWESResearch Report,5, 15.115.19.

Tatham, R. T., 1982, Vp/Vs and lithology: Geophysics, 47, 336344.Tatham, R. T., and Goolsbee, D. V., 1984, Separation of S-wave and

P-wavereflections, offshore western Florida: Geophysics, 49, 5,493508.

Tessmer, G., and Behle, A., 1988, Common reflection point data stack-ing technique for converted waves: Geophys. Prosp., 36, 671688.


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