1.1 M

The mmiliar wtation restaff. If asure to technicabefore rsome prmight beemphasimay notModifyirametersversely, sign par

Geophmore cuand intefocal potion wildifferentcome a v

Possibearly staset asidresourceinto choplanningin somemuch efrom theof ownethe field3-D survpartner program

f doing the very best technical job in 3-D designquisition.

BJECTIVES

Ini s

. The geophysicist as part of the exploration/ation team.ANAGEMENT ATTITUDES

anagement of an oil company needs to be fa-ith the acquisition, processing, and interpre-quirements that a 3-D survey may place on its companys management has had prior expo-3-D seismic surveys, less education by thel staff (usually the geophysicists) is necessaryecommending a 3-D survey. There may beeconceived ideas as to the final products that delivered at various stages. It is important toze that success or failure in a past 3-D survey necessarily be duplicated in future programs.ng the design, acquisition, and processing pa- can make significant improvements. Con-results may be less than expected if poor de-ameters are chosen.ysicists may find themselves serving one orstomers. Once 3-D data have been acquiredrpreted, the interpreted data set will become aint for several people because the interpreta-l be delivered to team members that practice disciplines (Figure 1.1). The data also be-aluable asset with resale value.le partners may need to be informed at ange about the planned operations so they can

pect oand ac

1.2 O

tial Consideration

Fig. 1.1exploite the anticipated financial and personnel s. They may wish to have significant inputosing the area for the 3-D survey, or in the design, or they may wish to contribute

other manner. Obtaining their approval isasier if they have been intimately involved start. This approach gives partners a sense rship. Sometimes the company that operates is not the one that contributes most to a ey. It is possible, for example, that another

in the area could operate an extensive seismic. Information exchange is an important as-

A coma 3-D suare listein mindAny seprocesseresults tuate all straints

Most data list

11pany needs to establish early and clearly whyrvey is to be recorded (some possible reasonsd in Figure 1.2). These goals must be kept during all phases of the planning process.

ismic program must be planned, recorded,d, and interpreted in time to deliver sufficiento the owners of the data so that they can eval-results along with other information and con-that they may have.of the reasons for recording the 3-D seismiced in Figure 1.2 do not need any explanations.

For exafor betteferencesover theyears shpracticecoming

1.3 IN

Both lnology ttice is pcially reSuccess by usincompanfrom 13%3-D techsuccess stant, thhas show

SmallD survesurrounnies ma100s of purposesition coparticipment wbut also

earachv c

e rics d choice over 2-D acquisition.y major oil companies have the necessary re-s and expertise to plan, acquire, process,

2 Initial Considerations

Fig. 1.2.survey. 98

100

.le ftemple, reservoir monitoring may be essential

r production practices in large fields. The dif- observed in 3-D seismic surveys recorded same field with a separation period of severalow the progress of depletion and flooding

s. Such 4-D or time-lapse surveys are be-more common.

DUSTRY TRENDS

arge and small companies now use high-tech-ools to obtain data improvements. This prac-articularly true for the energy sector, espe-garding the use of 3-D seismic technology.ratios for oil companies have been increased

Onethe yeCanadmic teis an awill beout thtion ppacitiefavore

Mansource

Different reasons for shooting a 3-D seismic

3-D

su

itab

le a

rea

(% s

ho

t)

1

90

80

70

60

50

40

30

20

10

0

Fig. 1.3suitab1995 ag 3-D data. In a worldwide study, one largey registered an increase in their success rate

in 1991 using 2-D data to 44% in 1996 usingnology extensively (Ayler, 1997). While the

rate using 2-D data alone has remained con-e success rate using 3-D seismic technologyn a dramatic improvement.

independent companies may acquire small 3-ys to help detail relatively small land holdingsding existing production. Larger oil compa-y acquire 3-D data over larger areas of 10s orkm2. Often these surveys are for exploratorys only. One important new trend is that acqui-ntractors are now offering to record huge 3-D

ation surveys not only in the offshore environ-here the practice has been done for a while, onshore.

and intesmall-siexperiening witheasier tosurveys

1.4 FI

Cost fsions abploratiodense gformatioeconomholes ancovery wstimate for North America indicates that by 2007, essentially all of the area in the US and that is suitable for the application of 3-D seis-nology will be covered (Figure 1.3). Since thiserage estimate, there will be many areas thatovered more than once by a 3-D survey with-intention of doing 4-D surveys. With acquisi-es falling at a fast rate and higher channel ca-being available, 3-D acquisition becomes the

200720031999

Rapid Growth

Slow Growth

199519917

Application of 3-D seismic technology to areasfor 3-D data acquisition in North America (Koen,r A. Cranberg, Aspect Management Corp.).rpret 3-D data in-house, while medium andze oil companies rely on the knowledge andce that consultants offer. By constantly deal- the subject of 3-D data acquisition, it is much be proficient at planning and operating such

.

NANCIAL ISSUES

actors play an important role in making deci-out the expenditures for a 3-D survey. The ex-n team must prove to management that arid of geophysical data tied to geological in-n from existing wells provides significant

ic benefits by reducing the number of dryd overall costs. In the past, at least one dis-ell in a particular prospect area was needed

to convince management to spend additional re-sources on 3-D seismic data. Recently there has been atrend toplorator2-D probe just alems ofvarious tainties quiring tive evaconfidennical inf

Budgeearly plmay resusurvey mmanagebudget nsurvey technicawho ultany unadoes theor at irrtain timschedule

Mananomic rpotentiawarrantthan notwell baswell be ploratiouation. Aand resuThe cost

On a ptions, ashallownomicalfill locatdictate adrilling For examdrilling pling inthe reser

Even wells wiD survevey (Fig

$,0

6

5

d

00et. Under current economic conditions, thist of money might pay for 10 mi2 or more of 3-D

c data.d (1998) provides a more thorough analysis oflue of 3-D data through decision tree analysisn guide the explorationist in his or her deci-

Figure 1.5). There are numerous decision pointsdeciding whether to drill and/or whether to ac-dditional 2-D or 3-D seismic data. One can as-rtain probabilities to particular exploration re-

hat can be achieved with 3-D seismic data byexpected value concepts (Figure 1.6, Table 1.1).the terminology in Table 1.1, the probability ofnomic success Pes is

Pes Psource Pmigration Preservoir Ptrap, (1.1)

e expected monetary value EMV is

EMV NPVsuccess Pes + NPVfailure Pef. (1.2)

1.4 Financial Issues 3

Cost

.. use 3-D technology even in a purely ex-y environment. The cost of acquiring severalgrams possibly spread over many years mays high as a 3-D survey. In addition, the prob-

interpreting and consistently incorporatingvintages of 2-D data lead to inevitable uncer-that may be insurmountable. Therefore, ac-3-D seismic data provides a more cost-effec-luation of a prospect by providing increasedce in the seismic interpretation and new tech-

ormation.t constraints need to be made clear at the

anning phase; otherwise, unrealistic designslt. If the budget numbers are too low, the 3-Day be under-designed and unable to meet

ment expectations. On the other hand, if theumbers are too high, the designers of the 3-D

may over-design in areal extent or in otherl specifications. Important considerations are:imately controls the budget; who approvesnticipated changes, especially cost overruns; planning committee meet on particular datesegular intervals; and how difficult is it to ob-ely approvals in order to maintain the time?

gement needs to be able to evaluate the eco-ate of return for any project in question. Thel of a prospect and its associated risk must the cost of a 3-D seismic survey. More often, a 3-D survey is difficult to justify on a single-is. However, a 3-D seismic survey may very

worthwhile if dry holes are to be avoided. Ex-n wildcat wells are commonly that type of sit-

3-D survey may make a wildcat less wildlt in the drilling of significant discoveries.

of missed opportunities is very high.roject that has numerous development loca-

nd even for low-cost drilling of relatively wells, 3-D seismic surveys are often eco-ly justifiable. If many step-out wells and in-ions are anticipated, project economics may 3-D survey. Similarly, plans for horizontalmay require tightly controlled seismic data.

ple, if the target horizon is relatively thin,engineers may need high-resolution sam-

all three dimensions to keep the drill bit invoir.

a small increase in the success ratio of drillingth a 3-D survey (e.g., 1:5) versus without a 3-y (e.g., 1:6) could justify the cost of a 3-D sur-ure 1.4). Assume drilling 6 wells at a dry hole

cost ofof $500

This$500,0data samounseismi

Heathe vathat casions (when quire asign cesults tusing Using an eco

and th

Fig. 1.4survey500,000 each versus drilling 5 wells at a cost00 each with 3-D data.

$500K $3,000,000 without 3-D

$500K $2,500,000 with 3-D

ifference $ 500,000

example indicates that one might have available to invest in the acquisition of a 3-D

Cross-overPoint

Cost of 3-D Seismic

Lower F

inding C

ost

(Higher

Success

Rate) w

ith 3-D

High

er Fi

ndin

g Co

st

(Low

er S

ucce

ss R

ate)

with

out 3

-D

Increasing Number of Wells

Project economics for wells and a 3-D seismic

Through such analysis one can establish the maxi-mum economic value to ascribe to a 3-D seismic sur-vey. The(EMV) omines thD survea possibNPV ar(1995) pexploratwells ca

Costswhere tof equipgeograporder oftion. Hifold surhand, sp

3-Ds (Servodio et al., 1997) can provide costs. An analysis of the economics of different ac-on parameters is essential in evaluatinger high S/N ratios and small bin sizes are war-. Such analysis is possible by decimating exist-

4 Initial Considerations

PsourcePmigrationPreservoirPtrapNPVsuccesNPVfailurePesPefEMVVOI

Fig. 1.5. Decision tree analysis to guide the explorationdecision process.

. Probability of economic success (Pes) versussent value (NPV). difference in the expected monetary valuef the project without and with 3-D data deter-e maximum amount that can be spent on a 3-

y. Total project economics, cost of money, andle increase or decrease in the total project

e not taken into account in Figure 1.6. Ayloroints out that many 3-D surveys add value toion and development projects because moren be drilled. for 3-D surveys vary depending on the areahe survey is to be conducted, the availabilityment and crews, and the complexity of thehy. In general, one can expect to pay on the $10 000 to $50 000 per km2 for data acquisi-gh-resolution work for smaller bins and high-veys can exceed those costs. On the otherarse 3-D surveys (Bouska, 1995) or very fo-

cused savingquisitiwhethranted

Fig. 1.6net preTable 1.1 Profitability Ta

Probability of hydrocarbon sourceProbability of migration of hydrocarbonsProbability of reservoir/porosityProbability of seal/trap

s Net present value of successful wellNet present value of dry wellProbability of economic successProbability of economic failureExpected monetary valueValue of information (e.g., 2-D, 3-D, interpretations)Required success ratio for single wellble

w/o 3-D with 3-D % change90% 90% 0%80% 80% 0%70% 80% 14%30% 40% 33%

$8,000,000 $8,000,000($1,500,000) ($1,500,000)

15% 23% 52%85% 77% 9%

($63,600) $688,800($752,400)

16% 22% 39%

ing data sets and interpreting the individual data setsseparately (Schroeder and Farrington, 1998).

Processing costs vary but are usually in the range of510% of acquisition. A detailed interpretation shouldbe in the same cost range as processing.

1.5 TARGET HORIZONS

A 3-D seismic survey should be designed for themain zone of interest (primary target). This zone willdetermine project economics by affecting parameterselection for the 3-D seismic survey. Fold, bin size,and offset range all need to be related to the main tar-get. The direction of major geological features, such asfaults or channels, may influence the direction of thereceiver and source lines.

Secondary zones or other regional objectives mayhave a significant impact on the 3-D design as well. Ashallow secondary target, for example, may requirevery short near offsets. Deeper regional objectives andmigration considerations may dictate that the far off-set of the survey be substantially greater than themaximuat the ta

1.6 SEAC

Prepawill avoclose to

meeting critical deadlines such as land sales, lease ex-pirations, or bid submission dates. The technical teamshould update this time line as the project progresses,so that the parties involved are kept abreast of thechanges. A realistic time line needs to be establishedearly so that expectations are on track with the overallprocess of obtaining the data (Figure 1.8). The time re-quired for each step in the time line varies widelyfrom area to area. A small 3-D survey can be com-pleted from scouting to drilling within 6 to 8 weeks,while larger surveys in difficult access areas may de-mand two years or more. In-depth knowledge of localtime requirements is essential.

A scouting trip to the 3-D area may provide sub-stantial information for the design of the 3-D survey;e.g., existing cut lines may dictate line intervalsand/or direction, or surface cover could influence dynamite hole depth and charge size. All technical parameters must be kept in mind when designing a

1.6 Sequence of Events for Data Acquisition 5

Fig. 1.7.targets. .m stacking offset used in the fold calculationrget level (Figure 1.7).

QUENCE OF EVENTS FOR DATAQUISITION

ring an overall time line for data acquisitionid surprises and keep expectations somewhatreality. This time planning should also help in

Primary target horizon versus secondary Fig. 1.8 Time line of a 3-D seismic program.

survey. The design may need to be updated as moreelements and parameters of the time line becomeknown. latory aptory bodto consias foresrection o

Criticcrews avthe projcountrymajor dclearingten hardten do navailabigoes wrdamagebrought

OtherWhat kcustomais involvsubmissto put ators neetent? Thlaid outneed tocost/souto namefor an everyontractor hing on acontracttant to nneeds othat also

Manyof the jobulldozeusually includedmust bearrive asurvey. the acquof allowsignifica

Turnkquisition

that the crew will work fast. Some element of supervi-sion must be introduced to obtain the required quality

iewjo

eoa n.

rrs

nmuheeetiou

ais

veee es

ess

rovot .

o e

hg

ic lwegbld

p

6 Initial ConsiderationsOperators should request all necessary regu-provals and stay in close contact with regula-ies to ensure smooth operation, remembering

der past survey requirements and costs suchtry regulations, damages, reseeding, and cor-f erosion problems.

al questions such as Are experienced 3-Dailable locally? need to be answered early in

ect. If crews need to be shipped across the or even from another country or continent,elays should be expected, especially when customs. Some 3-D seismic equipment is of- to get through customs because officials of-ot understand the technology. Knowing the

lity of spare parts is important if anythingong in the field. For example, if cables becomed, how much replacement equipment can be in and how long will it take? key questions that need to be considered are:inds of data acquisition bid procedures arery at the prospect location? How much timeed from requesting such bids to their actual

ion? How much time do the contractors need reasonably accurate bid together? Do contrac-d to research local conditions, and to what ex-e oil company may have bidding procedures in a very particular manner, e.g., bids may be presented in a form of cost/km2,rce point, cost/day, or total project cost, just a few variations. The content requirements

acquisition bid should be clearly known toe involved in the bidding process. If the con-as to sign a standard contract before embark-

job, the oil company may want to include this at the stage of requesting a bid. It is impor-egotiate a satisfactory contract that meets thef the oil companys particular situation and reflects the political environment. acquisition contractors will subcontract partsb such as surveying, shot-hole drilling, andr work. The costs of these subcontracts areconsidered extras and therefore may not be in the overall cost/unit basis. A best effort

made to estimate the extent of these extras tot a realistic total cost figure for a 3-D seismicThese so-called extras may more than doubleisition cost. The uncertainties in cost becauseances for bad weather can also represent ant portion of the total cost.ey quotes help set the price for most of the ac- costs. This bidding policy assures a client

of servthe crother servicetion.

Somcrew feral yegotiateplannierationsuch ataintiekets.

Oftenot coor inslimit tand thtives rprotecsuch cthen o

Permto obtearly aD surmay nline ofany ming seachangsourcelandowline acmay apermicernedway tdamagcrew tmittinline kmof cho

If alands mic opLarge desiraplannerationce. Daily rates, on the other hand, do not give an incentive to work fast. However, if no

bs are waiting for the crew, the best level ofpossibly can be obtained via a daily rate op-

companies may choose to hire an acquisitionr an entire acquisition season or even for sev-rs. Under such circumstances, the need to ne-every seismic program disappears and betterg needs to be implemented for continuous op- The price guarantee that usually accompaniesangements is a big advantage over the uncer-that industry experiences in fluctuating mar-

the legal contract that a contractor provides isprehensive. If any field problems, accidents,

fficiencies arise, an incomplete contract may legal protection for the acquisition contractor

client. It is advisable to have legal representa-view the contract and ensure that sufficienton exists for both parties. If experience withntracts does not exist within the organization,tside advice should be requested.its may be required from land surface ownersn entry. Such permits should be requested as possible because permit issues can affect a 3-y in a number of different ways. Permittingd to be started significantly earlier in the time

Figure 1.8. Landowners may not want to seember of an acquisition crew during the grow-on, even if crop damages are to be paid. Slight in the design or layout of the receivers andmay make a huge difference to particular

ners. For example, by moving a portion of ass the fence to neighboring noncrop land, oneid crop damages and pay another landowner

fees. This is a beneficial scenario for all con-Good rapport with landowners will go a longassuring access to their lands, and keepings to a minimum will help the next seismicat wants to work in the same area. Often per-by km2 is less expensive than permitting by. Permitting by area also gives more freedome in the field.andowner controls a high percentage of theithin a 3-D survey and is opposed to the seis-ration, the entire program may be in jeopardy.aps of no coverage on a 3-D survey are un-e, and such opposition may cripple the survey and perhaps cancel part of the explo-rogram.

In at least one U.S. state (e.g., Texas), it is illegal torecord a geophysical measurement of any kind over an-other owowner (gfusion apreted. Mpermits against pare trimstacked not undsee AAPBurr Ran

Key qHow muWhich ctribute tWill theof bid su

If thelimited then a 2essentiareceivercially foing consOn a larthe requveys ma(such asquencesSometimenough testing a

Surveperimetethe specing Systaccuracymore tr(EDM) well-estaaccuracyvertical few centeach stachainerscation. Gdeep ravther GPS

Shot-hlowing, ally the

recording crew arrives, assuming that all source para-meters have been previously established. This drilling

leg o

atc

s atitequncprm o

trt s

rere i ere s nnreisn

ofreorrol, renierae ererllc

enc s tgse b ne c

1.6 Sequence of Events for Data Acquisition 7ners mineral rights without a permit from thateophysical trespass). There is considerable con-s to how the relevant laws should be inter-

ost operators are now being diligent to obtainover all relevant lands to protect themselvesossible liability. Many operators of 3-D surveys

ming their surveys to ensure that there are notraces over areas not covered by permits (e.g.,ershooting corners). Interested readers shouldG Explorer, June 1995, for a discussion of thech case and related issues.uestions to consider include the following:ch is known about the operating conditions?

ontractors have experience in the area to con-o the successful operation of such programs? contractor share this information at the timebmission or only if they win the contract?

knowledge of local operating conditions isor data quality to be expected is unknown,-D test line may be required and is sometimesl for correct parameter selection. Source and array tests are much easier to conduct, espe-r small 3-D surveys, when a 2-D test line is be-idered as a first evaluation of the prospect.

ge 3-D survey, it might be justified to conductired tests at the start of the survey. Large sur-y require a variety of sources or receivers in a transition zone), and several test se-

may be performed throughout the survey.es the local conditions are known wellthat a 3-D survey may proceed without anyt all.yors need to go to the field and establish ar of the 3-D seismic survey before filling in

ific source and receiver lines. Global Position-ems (GPS) technology provides good survey and is a faster surveying technique thanaditional Electronic Distance Measurementdevices. Differential GPS, which relies on ablished local base station, offers even greater; its horizontal accuracy is 1 m while the

accuracy is 2 to 3 m presently. Accuracies of aimeters can be achieved with longer time ontion. Once the grid has been established, will mark every source and receiver group lo-PS does not work well in dense tree cover or inines where satellites cannot be seen. For fur- information, see Harris and Longaker (1994).ole drilling may commence immediately fol-or even concurrent with, the surveying. Usu- entire 3-D area will be drilled before the

schedudrillinchancecrew.

Vibrtion onalwaycorrelaThese the acthan o

If a an atteTesting(or anybe inspresen

Thein a pnecteddigitalrecordrequirphoneble coto the transmdio sigstead data acally fa contcontro

Theelectroand thshow t

Somthe ovwhethcerns adata-relengthseismi

FieldimaginprocesshouldSurveyand ththe pro reduces noise interference between theunits and the data recording. There is also nof the drillers being in the way of the layout

or trucks or buggies may start sweep produc-e the sweep parameters have been tested. It isdvisable to complete phase, peak force, and

on tests before going into production mode.sts should be repeated several times duringisition program and should be done moree daily.ogram does not allow or warrant any testing,pt should be made to find past tests or data.

is important for both dynamite and vibratorther source) data acquisition. Such tests may

uctive for any future programs, even if theurvey cannot benefit from the test results.cording crew places receivers on the grounddetermined array. The geophones are con-n receiver groups, which then transmit theinformation in a variety of ways to the. Cable-based distributed recording systemsa continuous cable connection from the geo-to the recorder, thus one can walk out the ca-ections from any geophone all the way backcording truck. An alternate technique for datasion is the telemetry system, which uses ra-als to transmit data to the recording truck in- cables. In the case of the I/O RSR system, recorded locally and then retrieved periodi- storage on tape. For this system, the radio isl unit for initiation of recording and qualitybut it is not used for data transmission. corder unit (dog house) has a complete set ofcs that allows data correlation (for vibrators) recording and display of shot records thatces corresponding to all geophone groups.crews operate on a 24-hour basis to reducehead cost per source point. One has to check local customs and/or laws and safety con-ow such around-the-clock operation. Limitingording activity to dawn-to-dusk significantlys the number of days needed to record a 3-Durvey.apes are sent to the processor for analysis and of the data, or more recently, the data can bed in the field. The choice of the processore decided before the crew enters the field.otes need to be reduced to final coordinates,final survey geometry must be forwarded toessor.

Interpretation on paper and/or on a workstationusually gives a clear idea of the geological variationsin the aor devesufficiencomplet

1.7 EN

Envirdays wOne shosible dforestednecessarto proteprotect cult terrshot-homize da

Wildlsuch astransitiocertain rodentstransmilessens such as bles. Solocal intto prevefere dircent trena recogneffectivegood coare a wi

Weathseismic snow mthat datment mwant toimproveground cover menter thas an inseveral ing crewconditiopersonn

1.8 SPECIAL CONSIDERATIONS OF 3-DVERSUS 2-D DATA ACQUISITION

npronro tod

l fl it l cmeatto

antiar sus)r nds,

Tseapduitilla,thal . pr o

ch cuitind liuoutatathro

E

re-Ded

8 Initial Considerationsrea of the 3-D survey. Drilling of explorationlopment wells should commence only aftert time has been allotted for a thorough ande interpretation.

VIRONMENT AND WEATHER

onmental issues play an important role in to-orldespecially in seismic data acquisition.uld protect the environment as much as pos-

uring all field operations. Line cutting in areas should be limited to the smallest widthy. Small jogs in the lines are often requested

ct the pristine appearance of the woods and towild life. In mountainous areas or other diffi-ain, helicopter support may be essential for

le drilling or for laying receiver cables to mini-maging effects on the environment.ife protection issues have to be addressed mating seasons and migration paths. In an zone, fish spawning might be a concern at

times of the year. In some parts of the world, may chew cables and hinder successful datassion. The use of wooden pegs for station flagsthe damage to farm equipment and animals,cows, which often chew station flags and ca-

me areas are so environmentally sensitive thaterest groups may lobby government officialsnt any seismic operation, or they may inter-

ectly with seismic or drilling operations. Re-ds in the environmental industry have shownition that stopping the seismic operations alsoly stops oil and gas exploration; therefore,mmunity relations in advance of operationsse investment in time and effort.er conditions may constrain operation of aprogram to certain times of the year. Rain oray alter ground conditions to such a degreea quality is severely diminished. Crew move-ay also be hindered. In cold climates, one may wait for frost before laying out geophones to the coupling of the geophone spikes to theand to minimize surface damages. Snoway need to be removed to allow the frost to

e ground rather than allowing the snow to actsulator. Often receiver lines need to be clearedtimes if significant new snowfall occurs dur- operations. In warmer climates, extreme heatns may hinder the effectiveness of the crewel and may pose a serious safety hazard.

Onemore quisitimid-pposedforesteprovaprovaing cuwhichequip2-D dment theft,

Spacoarsea 3-D surveycoarsedips aD linenorm.on thecent pthe inacquis

Finaan arement imuthsirablea 2-D rectionbetter

OneD versacquisarea aof 2-Dcontintion o2-D dwhen to imp

1.9 D

Figuonal 3ogy useeds to specify the objectives of a 3-D surveyecisely than for a 2-D survey because the ac- parameters are more difficult to change in

gram. For example, with a 3-D survey (as op- 2-D) much more line cutting is required in

areas. This makes it harder to obtain ap-rom regulatory bodies, and even when ap-s granted, one may be limited to using exist-ines or be restricted to hand-cut receiver lines,an slow the operation. On a 3-D survey, thent stays on the ground much longer than in

a programs. This factor exposes 3-D equip- more environmental, vehicular, weather,

d wildlife damage.l sampling in 3-D programs is usually muchthan in 2-D programs (e.g., 20 to 40 m bins inrvey versus 5 to 15 m trace spacings in 2-D. It is important to decide whether thissampling is sufficient to resolve structural to properly image geological features. For 2-

linear source and geophone arrays are thehe effects that source-receiver azimuths have geophone (or source) arrays is a topic of re-ers and research. There is no consensus yet instry on the type of arrays to use in 3-D dataon.y, 3-D sources and receivers are laid out over and 3-D recordings have an azimuthal ele-at is not present in 2-D efforts. Good az-distributions are usually, but not always, de-

If any out-of-the-plane phenomenon exists inofile, often one is unable to determine the di-f its cause. In contrast, 3-D migration has aance of properly positioning such anomalies.

an argue at length about various aspects of 3-s 2-D imaging. 3-D data have a common set ofon and processing parameters over a large therefore are easier to interpret than a seriesnes of various vintages. A 3-D data volume isus, and one may extract profiles in any direc-

of this volume. However, in some situations, may be more beneficial than 3-D data, e.g.,ere is a need to gain a regional perspective orve local resolution with a small trace spacing.

FINITIONS OF 3-D TERMS

s 1.9 and 1.10 show a plan view of an orthog- survey that illustrates most of the terminol- in this book.

Note: howeverimperialRather tial unitsthat wou30 m bin

Box (so3-D surby two ceiver lirepresencontainsfold arebin locatributionshortestlargest other wCMP bin

1.9 Definition of 3-D Terms 9

Fig. 1.9.This book uses SI notation as a standard;, most numerical examples are presented in units as well, and these are printed in italics.han directly converting metric units to imper-, we have chosen the natural imperial unitsld be used in the particular situation (e.g., a size might be equivalent to a 110 ft bin size).

metimes called Unit Cell) In orthogonalveys, this term applies to the area bounded adjacent source lines and two adjacent re-nes (Figures 1.9 and 1.12). The box usuallyts the smallest area of a 3-D survey that the entire survey statistics (within the full-a). In an orthogonal survey, the midpoint ted at the exact center of the box has con-s from many source-receiver pairs; the

offset trace belonging to that bin has theminimum offset of the entire survey. In ords, of all the minimum offsets in all s, the minimum offset in the bin at the center

3-D survey layout terms.

Fig. 1.10

of the bogies attof ways

CMP Bially has. 3-D survey bin terms.

x has the biggest Xmin. Different layout strate-empt to deal with this concept in a variety .

n (or Bin) A small rectangular area that usu- the dimensions (SI 2) (RI 2). All mid-

points that lie inside this area, or bin, are assumed tobelong to the same common midpoint (Figure 1.10).In other words, all traces that lie in the same bin willbe CMPOn occatraces arorder todata smtion bec

Cross-linal to re

Fold Twithin aerage fobin to bi

Fold Tathat neeup full fbetweencause onof the m

In-line Dceiver li

Midpoitween anel rececreate 4tered an

Migratineeds tomigratiowidth dsurvey. than an migratio3-D migof 3-D v

Patchrecord dvey. Theparallel survey the surv

Receivethroughregular stations

the in-line dimension of the CMP bin. Normally thefield recorder cables are laid along these lines andgeophones are attached as necessary. The distance be-

sh ot

rie -s r

l- os

e asmini

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10 Initial Considerationsstacked and contribute to the fold of that bin.sion, one may choose the area over whiche stacked to be different from the bin size in increase stacking fold. This introduces someoothing and should be performed with cau-ause it affects spatial resolution.

ne Direction The direction that is orthogo-ceiver lines.

he number of midpoints that are stacked CMP bin. Although one usually gives one av-ld number for any survey, the fold varies fromn and for different offsets.

per The width of the additional fringe areads to be added to the 3-D surface area to buildold (Figure 1.11). Often there is some overlap the fold taper and the migration apron be-e can tolerate reduced fold on the outer edgesigration apron.

irection The direction that is parallel to re-nes.

nt The point located exactly halfway be- source and a receiver location. If a 480-chan-iver patch is laid out, each source point will80 midpoints. Midpoints will often be scat-d may not necessarily form a regular grid.

on Apron The width of the fringe area that be added to the 3-D survey to allow propern of any dipping event (Figure 1.11). Thisoes not need to be the same on all sides of theAlthough this parameter is a distance ratherangle, it has been commonly referred to as then aperture. The quality of images achieved byration is the single most important advantageersus 2-D imaging.

A patch refers to all live receiver stations thatata from a given source point in the 3-D sur- patch usually forms a rectangle of severalreceiver lines. The patch moves around the

and occupies different template positions asey moves to different source stations.

r Line A line (perhaps a road or a cut-line bush) along which receivers are laid out atintervals. The in-line separation of receiver(receiver interval, RI) is usually equal to twice

tweento as tlayinggeome

Scattescattergle issourceceiver

Signasignalated a

Sourcsourcetaken sourcethe cocross-lmidpoexactlywith ttance bthe sothe sosquare

Sourcsity), source nels, Nthe fol

Supermaxi bins. Gdetermtenuat

Swathmeaniswathstationond, ttry, rathere aassoci

Templnumbuccessive receiver lines is commonly referrede receiver line interval (or RLI). The method ofut source and receiver lines can vary, but the

ry must obey simple guidelines.

ng Angle Assuming the presence of a pointr (diffraction point) at depth, the scattering an-the angle between the vertical downgoingcatterer raypath and the upgoing scatterer-re-

aypath.

to-Noise Ratio The ratio of the energy of thever the energy of the noise. Usually abbrevi-S/N.

Line A line (perhaps a road) along whichpoints (e.g., dynamite or vibrator points) aret regular intervals. The in-line separation of (source interval, SI) is usually equal to twicemon midpoint (CMP) bin dimension in thee direction. This geometry ensures that the

nts associated with each source point will fallone midpoint away from those associated

e previous source point on the line. The dis-tween successive source lines is usually called

rce line interval (or SLI). SLI and SI determinerce point density (or SD, source points perilometer).

Point Density (sometimes called shot den-D The number of source points/km2 oroints/mi2. Together with the number of chan-, and the size of the CMP bin, SD determines

.

in This term (and others like macro bin orin) applies to a group of neighboring CMPouping of bins is sometimes used for velocitynation, residual static solutions, multiple at-n, and some noise attenuation algorithms.

The term swath, has been used with differentgs in the industry. First, and most commonly, aquals the width of the area over which source are recorded without any cross-line rolls. Sec-e term describes a parallel acquisition geome-

er than an orthogonal geometry, in whiche some stacked lines that have no surface linesed with them.

te A particular receiver patch into which a of source points are recorded. These source

points mform,

Tem

Xmax Ton shoothe half-externallarge Xm

Xmin Ttimes redescribeis necess

Assumof 60 m (110 ft lel receiva diagon

The vset to bebox. In

tentionally coincident at the line intersectionsplicity.

The mute distance for a particular reflector.a

1.9 Definition of 3-D Terms 11

Fig. 1.11ay be inside or outside the patch. In equation

plate = Patch associated source points.

he maximum recorded offset, which dependsting strategy and patch size. Xmax is usuallydiagonal distance of the patch. Patches with source points have a different geometry. Aax is necessary to record deeper events.

are infor sim

XmuteAny tr

. 3-D survey edge management terms.he largest minimum offset in a survey (some-ferred to as LMOS, largest minimum offset) asd under Box. See Figure 1.12. A small Xminary to record shallow events.ing RLI and SLI of 360 m (1320 ft), RI and SI

(220 ft), the bin dimensions are 30 m 30 m110 ft). The box (being formed by two paral-er lines and the orthogonal source lines) hasal of:

Xmin (3602 3602)1/2 m 509 m

Xmin (13202 13202)1/2 ft 1867 ft

alue of Xmin defines the largest minimum off- recorded in the bin that is in the center of thethis example the source and receiver stations Fig. 1.12ces beyond this distance do not contribute to. Xmin definition.

the stack at the reflector depth. Xmute varies with two-way traveltime.

Chapter 1 Quiz

1. Define receiver line interval.2. What is migration apron?

3. How does one determine Xmin in an orthogonalsurvey (orthogonal source and receiver lines)?

4. How large is a super bin?

12 Initial Considerations

Initial ConsiderationsMANAGEMENT ATTITUDESOBJECTIVESINDUSTRY TRENDSFINANCIAL ISSUESTARGET HORIZONSSEQUENCE OF EVENTS FOR DATA ACQUISITIONENVIRONMENT AND WEATHERSPECIAL CONSIDERATIONS OF 3-D VERSUS 2-D DATA ACQUISITIONDEFINITIONS OF 3-D TERMSBox (sometimes called "Unit Cell")CMP Bin (or Bin)Cross-line DirectionFoldFold TaperIn-line DirectionMidpointMigration ApronPatchReceiver LineScattering AngleSignal-to-Noise RatioSource LineSource Point Density (sometimes called shot density), SDSuper BinSwathTemplateXmaxXminXmute

Chapter 1 Quiz

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copyright: 2000 Society of Exploration Geophysicists. Updated 2011.