3D OBC Seismic Survey Geometry Optimization Offshore Abu Dhabi_Jan 2012

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technical article

© 2012 EAGE www.firstbreak.org

first break volume 30, January 2012

3D OBC seismic survey geometry optimizationoffshore Abu Dhabi

T. Ishiyama,1,2* G. Mercado2 and K. Belaid2

IntroductionFor 3D seismic survey design, it is essential to understand the

geophysical requirements for achieving the business objectives

in the exploration, appraisal, and development of oil and gas

fields. We have to select survey parameters such as nominal

fold, bin size, and maximum and minimum offsets to meet

the required signal-to-noise ratio, signal frequency bandwidth,

and sharpness of focusing, as discussed by several authors

(e.g., Berkhout et al., 2001; Volker et al., 2001; Vermeer, 2002;

Galbraith, 2004). Furthermore, we must find a practical survey

geometry to meet the geophysical requirements. When we hunt

for it, we have to consider operational constraints imposed byequipment capability and productivity, which in turn affect the

survey time and cost. We naturally seek higher survey efficiency

within the operational constraints. Therefore, it is important to

optimize the survey geometry to satisfy not only the geophysi-

cal requirements but also the operational constraints.

Ocean bottom cable (OBC) seismic surveys are commonly

acquired offshore Abu Dhabi, United Arab Emirates due to

the shallow water depths and numerous scattered produc-

tion facilities. OBC seismic surveys have several advantages

(Bouska, 2008). One of them is that the receivers and airgun

sources are independently deployed, allowing acquisition

of high-fold, long-offset, wide-azimuth data. The flexibility

enables a variety of survey parameters and geometries to meetthe geophysical requirements.

Offshore Abu Dhabi, the main reservoirs are in the Lower

Cretaceous and Upper Jurassic successions, and are all carbon-

ate formations. It is not always easy to image the reflectors,

especially in the Upper Jurassic succession, due to the very low

acoustic impedance contrast.

Ishiyama et al. (2010) discussed the choice of 3D OBC seis-

mic survey parameters that would meet the geophysical require-

ments effectively and efficiently for a specific survey in the

region, based on the results of a feasibility study and a pilot sur-

vey. For an orthogonal geometry with receiver point and source

point intervals of 25 m, receiver line and source line intervals of

200 m, and wide-azimuth sampling, the nominal fold is 240 for

the natural bin size of 12.5 × 12.5 m2 with a maximum inline

offset of 3200 m and a maximum crossline offset of 3000 m.

This geometry was designated OR2B in Table 1 of Ishiyama et

al. (2010). For an areal geometry with parallel swath shooting,

receiver point interval of 25 m, source point interval of 50 m,receiver line interval of 400 m, source line interval of 50 m,

and wide-azimuth sampling, the nominal fold is 480 for the

natural bin size of 12.5 × 25 m2 with a maximum inline

offset of 3200 m and a maximum crossline offset of 3000 m.

This geometry was designated AR4A in Table 1 of Ishiyama

et al. (2010). Longer maximum offsets may be required when

survey targets are deeper, resulting in a higher nominal fold.

For example, the nominal fold changes to 300 for the geometry

OR2B and to 600 for the geometry AR4A in the natural bin size

if the maximum inline offset is increased to 4000 m.

Whilst retaining these fundamental survey parameters,

we have further analysed several geometry options to solve

limitations in equipment capability, in particular the limita-tions in the maximum number of receivers and length of

cables, and to pursue higher productivity. We then tried to

optimize the survey geometry. In this paper, we start with a

discussion about OBC seismic survey geometry, introduce a

methodology to analyse geometry options, and then discuss

several geometry options.

AbstractThe flexibility of 3D ocean bottom cable (OBC) seismic survey design allows a variety of survey geometries. Among the

infinite variations, we naturally seek higher survey efficiency within operational constraints whilst satisfying the geophysical

requirements. We have analysed several geometry and shooting options, such as zippers between panels, source line inter-

leave, flip-flop shooting, outboard shooting, and distance-separated simultaneous shooting (DS3), to show how the survey

geometry may be optimized to yield higher productivity within the limitations of the available equipment.

1 INPEX, Akasaka 5-3-1, Minato-ku, Tokyo 107-6332, Japan. Present address: Delft University of Technology, Faculty of Civil

Engineering and Geosciences, PO Box 5048, 2600 GA Delft, The Netherlands.2 ADMA-OPCO, PO Box 303, Abu Dhabi, UAE.* Corresponding author, E-mail: [email protected]



www.firstbreak.org © 2012 EAGE52

technical article first break volume 30, January 2012

The shot repeat factor refers to the number of repeated

shots at a source point due to a receiver line roll in thecrossline direction. It is defined as the source spread width

divided by the receiver line roll width (i.e., the number of

receiver lines to be rolled multiplied by the receiver line

interval). A higher shot repeat factor results from a source

spread that extends outside the receiver spread on both

sides in the crossline direction. If longer cables are available

so that the width of the receiver spread can be increased,

the shot repeat factor may be reduced, thereby improving

the productivity.

Geometry analysis

Our fundamental survey parameters, OR2B and AR4Apresented above, specify geometry type, receiver point and

source point intervals, receiver line and source line intervals,

nominal fold, bin size, and maximum inline offset. Therefore,

the only real flexibility is to change the aspect ratio or the

maximum crossline offset in a patch. Cooper (2004a, b) sug-

gested using the aspect ratio to maximize the productivity.

In addition, one of our natural requirements is a wide aspect

ratio to achieve the diversity of offset and azimuth sampling

for consistent imaging without illumination holes, and the

uniformity of offset and azimuth distribution for a consistent

stacking response without geometry footprints.

Nominal fold in the natural bin size at the maximum

inline and crossline offsets for an i-roll- j receiver line roll isdefined as

(1)

where M is nominal fold, Mi is inline fold, Mx is crossline

fold, X maxi is the maximum inline offset, SLI is the source

line interval, X maxx is the maximum crossline offset, and

RLI is the receiver line interval. Here, X max i = 0.5 ×

SSL and X max x = 0.5 × SSW , where SSL and SSW are

the source spread length and width. In Equation (1), SLI

should be replaced by the shot point interval, SPI , for an

OBC seismic survey geometry

OBC seismic surveys commonly use orthogonal and arealgeometries (Vermeer, 2002). Orthogonal geometry can be

considered as a collection of overlapping cross-spread

gathers. The source lines are regularly spaced and oriented

perpendicular to the receiver lines (Figure 1). Areal geometry

can be considered as a collection of overlapping receiver

gathers, in which receivers are arranged in a widely spaced

grid whereas sources are in a densely spaced grid. Areal

geometry is commonly acquired with parallel swath shooting

whereby the source lines are oriented parallel to the receiver

lines. The inline shot point interval is quite dense whereas

the crossline source line interval is often coarse (Figure 2).

The extent of these single-fold subsets is defined by theaspect ratio, i.e., the maximum crossline offset divided by

the maximum inline offset. Spatial continuity is enhanced by

maximizing the extent of these subsets in all directions.

In OBC seismic surveys, receivers usually require higher

effort than sources. There is often a limitation on the maxi-

mum number of receivers or the length of cables available,

and deploying and retrieving cables from the sea bottom is

time-consuming. Consequently, receivers are often arranged

in a widely spaced grid whereas sources are in a densely

spaced grid.

OBC seismic surveys share some characteristics with land

seismic surveys, and use some similar methodologies. OBC

surveys are commonly acquired with a receiver line roll inthe crossline direction (i-roll- j receiver line roll) whereby i

receiver lines are active in a patch, and j extra receiver lines

are rolled from one patch to the next in the crossline direc-

tion during the shooting of the active patch. The receiver

effort needs to be approximately balanced with the source

effort in a patch. The cable vessel should complete retrieving

extra cables from the previous patch and deploying them in

the next patch during shooting of the active patch, so that

the source vessel is not waiting on the movement of cables.

A perfect balance allows continuous field operations, and

thereby improves the productivity.

Figure 1 An orthogonal geometry. Blue lines are receiver lines, and red lines

source lines.

Figure 2 An areal geometry with parallel swath shooting. Blue lines are receiver

lines, and red lines source lines.



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technical article



ZipperLarge OBC seismic surveys are commonly acquired with zip-

pers in the inline direction, whereby the receiver spreads or

source spreads are overlapped between panels to produce

a uniform distribution of the nominal fold defined by

the maximum inline offset (Figure 3), as commonly used

in large land seismic surveys (e.g., Sambell et al., 2010).

Receiver zipper requires overlaps of receiver spreads

between panels. The zipper length or the receiver spread

length to be overlapped corresponds to the maximum

inline offset, increasing the number of zippers or panels of

a survey. Source zipper requires overlaps of source spreads

between panels, i.e., the source spread extending outside

the receiver spread on both sides in the inline direction. The

zipper length or the source spread length to be extended

again corresponds to the maximum inline offset, extending

the source spread in the inline direction. For both cases,

if longer cables are available for the receiver spread, the

number of zippers or panels in a survey is reduced, andproductivity is thereby improved.

Figure 4a shows crossplots of productivity versus aspect

ratio for i-roll- j receiver line roll of OR2B with receiver

areal geometry with parallel swath shooting. To produce a

uniform distribution of the nominal fold, Mi and Mx should

be integers. To make Mx an integer, the source spread width

should be an integer multiple, n, of the receiver line roll

width (Cordsen, personal communication), i.e.,

(2)

If i = 2 j, Mx = n × j for all integer n; otherwise, for even

integer n, Mx = n × i/2. The aspect ratio or the maximum

crossline offset can be solved for each i-roll- j receiver line

roll so that the nominal fold satisfies a minimum required

fold and is uniformly distributed. The required length of

cables for an i-roll- j receiver line roll is simply defined as

2 X maxi × (i+j), assuming that receiver line length is double

the maximum inline offset, which is 8000 m in our case.

Productivity in km2 per day of a survey with i-roll- j receiver

line roll is estimated as the survey area divided by the esti-

mated survey time, assuming rates for field operations suchas cable deploying speed, cable retrieving speed, shooting

speed, source line change time, and time for the recording

vessel to move between patches. In addition, the survey cost

can be estimated by assuming a daily cost and an efficiency

rate of field operations, taking standby and down times into

consideration.

Figure 3 A geometry with (a) receiver zipper and (b) with source zipper. Blue

lines are receiver lines, and red lines source lines. Patches in the N th panel and

the N+1th panel are shown separately and together, with overlap.

Figure 4 (a) Crossplots of productivity versus aspect ratio for i-roll-j receiver

line roll of OR2B with receiver zipper option. The colour classifies i of i-roll-j,

and the bubble size indicates required length of cables. (b) Crossplots of pro-

ductivity (on left vertical axis) and operations time per patch (on right vertical

axis) versus aspect ratio for 4-roll-j receiver line roll of OR2B with receiver zip-

per option. Colours indicate receiver effort in blue, source effort in red, and

consequent effort in green.






ratio for i-roll- j receiver line roll of OR2B with source zipper

option, and Figure 5b shows crossplots of productivity and

operations time per patch versus aspect ratio for 4-roll- j

receiver line roll of OR2B with source zipper option. In these

crossplots, for all 4-roll- j receiver line roll options, the source

effort becomes much higher due to the extended source

spread, and the receiver effort is significantly out of balance

with the source effort in a patch. However, the source zipper

improves the productivity more than the receiver zipper

because fewer zippers or panels are required for the survey

than that with the receiver zipper. For instance, the productiv-

ity of 4-roll-4 full swath roll improves from 1.69 to 1.82 km2

per day as receiver zipper is replaced by source zipper

(compare Figures 4b and 5b). The same trends are seen in

the crossplots of AR4A.

Source line interleave

Orthogonal geometry can be acquired with source line inter-leave, whereby the source lines in a patch are interleaved by

source lines from the previous and following patches. Source

line interleave allows a decimated source line interval in a

patch, but requires longer source line length in the patch to

satisfy the nominal fold (Figure 6).

zipper option. The colour classifies i of i-roll- j, and the

bubble size indicates the required length of cables. For a

set of plots of i-roll- j, smaller numbers of j fall at the lower

left, and larger number of j lie at the upper right. A larger

value of i improves the productivity, and larger number

of j increases the aspect ratio, in general. However, the

limitation in the available length of cables, of about 75 km

in the industry today, makes it difficult to apply larger

number of i and j. In these crossplots, the 4-roll-4 full

swath roll appears to provide reasonably high productivity

and aspect ratio within the limitation in available length

of cables. Figure 4b shows crossplots of productivity (on

left vertical axis) and operations time per patch (on right

vertical axis) versus aspect ratio for 4-roll- j receiver line

roll of OR2B with receiver zipper option. In the plots of

operations time per patch, the colour indicates receiver

effort in blue, source effort in red, and consequent effort in

green. In these crossplots, for all 4-roll- j receiver line roll

options, the source effort is significantly higher than thereceiver effort in a patch, so the source and receiver effort

is not well balanced.


line roll of OR2B with source zipper option. The colour classifies i of i-roll-j,

and the bubble size indicates required length of cables. Plots with required

length of cables more than 75 km are excluded. (b) Crossplots of productivity

(on left vertical axis) and operations time per patch (on right vertical axis) ver-

sus aspect ratio for 4-roll-j receiver line roll of OR2B with source zipper option.

Colours indicate receiver effort in blue, source effort in red, and consequent

effort in green.

Figure 6 An orthogonal geometry with source line interleave. Blue lines are

receiver lines, and red lines source lines. (a) N th patch. (b) N+1th patch. (c) N th

and N+1th patches.



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technical article



crossplots, for all 4-roll- j receiver line roll options, the

source effort becomes lower as a result of source line

interleave, mainly due to the decimated source line interval,

and consequently the productivity is improved. In addition,

the aspect ratio increases due to the wider source spread.

For instance, the productivity of 4-roll-4 full swath roll

improves from 1.82 to 2.14 km2 per day, and the aspect

ratio increases from 0.8 to 1.6 (compare Figures 5b and

7b). Similarly, within the 75 km limitation on the available

cable length, the 6-roll-3 receiver line roll with source lineinterleave improves productivity from 2.06 to 2.68 km2 per

day and aspect ratio from 0.38 to 0.75 as a result of source

line interleave (compare Figures 5a and 7a). However, for

all 6-roll- j receiver line roll options, the source effort is

significantly higher than the receiver effort in a patch, so

the effort is not well balanced (Figure 7c).

Flip-flop shootingAreal geometry with parallel swath shooting can be acquired

with flip-flop shooting in which two source lines are acquired

simultaneously from one sail line of the source vessel by


ratio for the i-roll- j receiver line roll of OR2B with source

zipper and source line interleave options, Figure 7b shows

crossplots of productivity and operations time per patch

versus aspect ratio for 4-roll- j receiver line roll of OR2B

with these options, and Figure 7c shows corresponding

crossplots for 6-roll- j receiver line roll of OR2B. In these


line roll of OR2B with source zipper and source line interleave options. The

colour classifies i of i-roll-j, and the bubble size indicates required length of

cables. Plots with required length of cables more than 75 km are excluded.

(b) Crossplots of productivity (on left vertical axis) and operations time per

patch (on right vertical axis) versus aspect ratio for 4-roll-j receiver line roll of

OR2B with these options. (c) Corresponding crossplots for 6-roll-j receiver line

roll of OR2B. Colours indicate receiver effort in blue, source effort in red, and

consequent effort in green.


line roll of AR4A with source zipper and flip-flop shooting options. The


cables. Plots with required length of cables more than 75 km are excluded. (b)

Crossplots of productivity (on left vertical axis) and operations time per patch

(on right vertical axis) versus aspect ratio for 4-roll-j receiver line roll of AR4A

with these options. Colours indicate receiver effort in blue, source effort in

red, and consequent effort in green.






ratio for i-roll- j receiver line roll of AR4A with source zipper,

flip-flop shooting, and outboard shooting options, Figure 10b

shows crossplots of productivity and operations time per

patch versus aspect ratio for 4-roll- j receiver line roll of

AR4A with these options, and Figure 10c shows corre-

sponding crossplots for 8-roll- j receiver line roll of AR4A.

In these crossplots, for all 4-roll- j receiver line roll options,

shooting alternately on each source line. Flip-flop shooting

halves the total number of sail lines for a source vessel.


ratio for i-roll- j receiver line roll of AR4A with source zipper

and flip-flop shooting options, and Figure 8b shows cross-

plots of productivity and operations time per patch versus

aspect ratio for 4-roll- j receiver line roll of AR4A with these

options. In these crossplots, within the limitation of avail-

able length of cables, the 4-roll-4 full swath roll appears to

provide good productivity and high aspect ratio compared

to other AR4A geometries. However, for all 4-roll- j receiver

line roll options, the source effort is much higher than

the receiver effort in a patch, so the effort is significantly

unbalanced in a patch.

Outboard shootingAreal geometry with parallel swath shooting can be

acquired with outboard shooting in which the source

spreads are arranged outside the receiver spread on bothsides instead of using a centrally located source spread, and

data are acquired in a racetrack shooting fashion (Bouska,

pers. comm.). Outboard shooting increases the aspect ratio

without expanding the source spread in the crossline direc-

tion or increasing the shot repeat factor (Figure 9).

Figure 9 An areal geometry with outboard shooting. Blue lines are receiver

lines, and red lines source lines. (a) N th patch. (b) N+1th patch. (c) N th and N+1t h

patches.


line roll of AR4A with source zipper, flip-flop shooting and outboard shooting

options. The colour classifies i of i-roll-j, and the bubble size indicates required

length of cables. Plots with required length of cables more than 75 km are

excluded. (b) Crossplots of productivity (on left vertical axis) and operations

time per patch (on right vertical axis) versus aspect ratio for 4-roll-j receiver

line roll of AR4A with these options. (c) Corresponding crossplots for 8-roll-j

receiver line roll of AR4A. Colours indicate receiver effort in blue, source effort

in red, and consequent effort in green.



57

technical article



roll of AR4A from 3.83 to 5.97 km2 per day (compare

Figures 10c and 14b).

Consequently, we selected the following geometry

options as the optimized survey geometries in our case,

as practical survey geometries that meet the geophysical

requirements and achieve higher survey efficiency within the

operational constraints:

(a) OR2B with 6-roll-3 receiver line roll, source zipper,

source-line interleave and DS3 options, providing an

the source effort barely changes as a result of outboard

shooting, but the aspect ratio increases (compare Figures 8b

and 10b). For instance, the aspect ratio of 4-roll-4 full

swath roll increases from 0.8 to 1.1. In addition, within

the limitation in available length of cables, the 8-roll-1

receiver line roll provides a significantly higher aspect

ratio (0.8 instead of 0.35) as a result of outboard shooting

(compare Figures 8a and 10a). However, for all 8-roll- j

receiver line roll options, the source effort is significantly

higher than the receiver effort in a patch, so the efforts in

a patch are not well balanced (Figure 10c).

Distance-separated simultaneous shooting (DS3)Beasley (2008) introduced simultaneous shooting for

marine seismic surveys. He suggested that the interfering

sources can be separated during processing. This approach

exploits spatial separation of the sources and geometry-

related filters such as pre-stack migration to achieve the

separation. Bouska (2010) introduced distance-separatedsimultaneous sweeping (DS3) for land seismic surveys,

producing independent records, uncontaminated by simul-

taneous source interference, for a range of offsets and

travel times spanning all zones of interest. He described

this concept simply as splitting the synchronized sources

far enough apart that distant interference noise arrives

after desired reflection signal. The source separation

distance is selected to allow sufficient travel time such that

the distant interference noise reaches the crossover later

than the travel time of interest. We applied these concepts

to OBC seismic surveys with simultaneously initiated

sources whose separation was more than double the maxi-mum inline offset, yielding separate unblended wavefields

within the offsets and travel times of interest (Figure 11).

DS3 with two source vessels halves a total length of sail

lines for each source vessel (Figure 12).

Figure 13a shows crossplots of productivity versus

aspect ratio for i-roll- j receiver line roll of OR2B with

source zipper, source line interleave, and DS3 options, and

Figure 13b shows crossplots of productivity and opera-

tions time per patch versus aspect ratio for 6-roll- j receiver

line roll of OR2B with these options. Figure 14a shows

crossplots of productivity versus aspect ratio for i-roll- j

receiver line roll of AR4A with source zipper, flip-flop

shooting, outboard shooting, and DS3 options, and Figure14b shows crossplots of productivity and operations time

per patch versus aspect ratio for 8-roll- j receiver line roll

of AR4A with these options. In these crossplots, for all

6-roll- j receiver line roll options of OR2B and 8-roll- j

receiver line roll options of AR4A geometry, the source

effort becomes significantly lower as a result of DS 3, the

receiver effort is well balanced with the source effort in

a patch, and the productivity is improved. For instance,

the productivity of 6-roll-3 receiver line roll of OR2B

improves from 2.68 to 4.84 km2 per day (compare Figures

7c and 13b), and the productivity of 8-roll-1 receiver line

Figure 11 An expected raw shot gather with DS 3.

Figure 12 (a) An orthogonal geometry and (b) an areal geometry with DS 3.

Blue lines are receiver lines, and red lines source lines.






line roll of OR2B with source zipper, source line interleave and DS 3 options.

The colour classifies i of i-roll-j, and the bubble size indicates required length

of cables. Plots with required length of cables more than 75 km are excluded.(b) Crossplots of productivity (on left vertical axis) and operations time per

patch (on right vertical axis) versus aspect ratio for 6-roll-j receiver line roll of

OR2B with these options. Colours indicate receiver effort in blue, source effort

in red, and consequent effort in green.


line roll of AR4A with source zipper, flip-flop shooting, outboard shooting

and DS 3 options. The colour classifies i of i-roll-j, and the bubble size indicates

required length of cables. Plots with required length of cables more than75 km are excluded. (b) Crossplots of productivity (on left vertical axis) and

operations time per patch (on right vertical axis) versus aspect ratio for 8-roll-j

receiver line roll of AR4A with these options. Colours indicate receiver effort

in blue, source effort in red, and consequent effort in green.

Figure 16 Crossplots of productivity versus aspect ratio for i-roll-j receiver line

roll of OR2B with source zipper, source line interleave, and DS 3 options. The


cables.

Figure 15 Bin attributes of (top) OR2B with 6-roll-3 receiver line roll, source

zipper, source line interleave and DS 3 options and of (bottom) AR4A with

8-roll-1 receiver line roll, source zipper, flip-flop shooting, outboard shooting

and DS 3 options. (a) Nominal fold in typical boxes. (b) The rose diagram in

a typical box (200 × 200 m 2 ). (c) Nominal fold in typical boxes. (d) The rose

diagram in a typical box (50 × 400 m 2 ).



59

technical article



Bouska, J. [2008] Advantages of wide-patch, wide-azimuth ocean-bottom

seismic reservoir surveillance. The Leading Edge, 27, 1662–1681.

Bouska, J. [2010] Distance separated simultaneous sweeping, for fast, clean,

vibroseis acquisition. Geophysical Prospecting , 58, 123–153.

Cooper, N. [2004a] A world of reality – Designing land 3D programs for

signal, noise, and prestack migration – Part 1 of a 2-part tutorial. The

Leading Edge, 23, 1007–1014.

Cooper, N. [2004b] A world of reality – Designing land 3D programs for

signal, noise, and prestack migration – Part 2. The Leading Edge, 23,

1230–1235.

Galbraith, M. [2004] A new methodology for 3D survey design. The Leading

Edge, 23, 1017–1023.

Ishiyama, T., Painter, D. and Belaid, K. [2010] 3D OBC seismic survey param-

eters optimization offshore Abu Dhabi. First Break, 28(11), 39–46.

Sambell, R., Al-Mahrooqi, S., Matheny, C., Al-Abri, S. and Al-Yarubi, S.

[2010] Land seismic super-crew unlocks the Ara carbonate play of the

Southern Oman Salt Basin with wide azimuth survey.First Break, 28(2),

61–68.

Vermeer, G.J.O. [2002] 3-D Seismic Survey Design. SEG, Tulsa.Volker, A.W.F., Blacquiere, G., Berkhout, A.J. and Ongkiehong, L. [2001]

Comprehensive assessment of seismic acquisition geometries by focal

beams – Part II: Practical aspects and examples. Geophysics, 66,

918–931.

Received 12 June 2011; accepted 27 October 2011.

doi: 10.3997/1365-2397.2011036

aspect ratio of 0.75 and uniform nominal fold of 300 in

the natural bin size of 12.5 × 12.5 m 2 with a maximum

inline offset of 4000 m and a maximum crossline offset

of 3000 m.

(b) AR4A with 8-roll-1 receiver line roll, source zipper, flip-

flop shooting, outboard shooting and DS3 options, pro-

viding an aspect ratio of 0.8 and uniform nominal fold of

640 in the natural bin size of 12.5 × 25 m 2 with a maxi-

mum inline offset of 4000 m and a maximum crossline

offset of 3200 m.

The bin attributes of these survey geometries (Figure 15)

show that these survey geometries satisfy the fundamental

survey parameters.

Figure 16 again shows crossplots of productivity versus

aspect ratio for i-roll- j receiver line roll of OR2B with source

zipper, source line interleave, and DS3 options. It should be

remembered that, in general, a larger number of i in i-roll- j

improves the productivity, and a larger number of j increasesthe aspect ratio. However, the limitation in the available

length of cables, which is about 75 km in the industry today,

makes it difficult to apply larger numbers of i and j. Some

desirable geometries are impractical due to this limitation. If

the availability of cables increases, more extensive receiver

spread can be allowed and practical survey geometries with

higher survey efficiency can be considered. We really look

forward to an increase in the available length of cables for

OBC seismic surveys.

Conclusions

As flexibility of 3D OBC seismic survey design allows avariety of survey geometries, the geometry should be selected

in such a way that it satisfies the geophysical requirements,

meets operational constraints, and produces higher survey

efficiency. We have analysed several geometry and shooting

options to deal with limitations in receive cable length, to

achieve higher productivity, and thus to optimize the survey

geometry. Whereas survey equipment and operations vary

field-to-field, contractor-to-contractor and time-to-time, this

exercise brings insights into achieving higher survey effi-

ciency within operational constraints.

Acknowledgements

We thank the managements of ADMA-OPCO and theshareholders, ADNOC, BP, Total, and INPEX, for their

support and permission to publish this paper. We also thank

Andreas Cordsen, Derrick Painter, and Jack Bouska for their

discussions on this study.

ReferencesBeasley, C.J. [2008] A new look at marine simultaneous sources. The

Leading Edge, 27, 914–917.

Berkhout, A.J., Ongkiehong, L., Volker, A.W.F. and Blacquiere, G. [2001]

Comprehensive assessment of seismic acquisition geometries by focal

beams – Part I: Theoretical considerations. Geophysics, 66, 911–917.

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Documents

3D OBC Seismic Survey Geometry Optimization Offshore Abu Dhabi_Jan 2012