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3D SEISMIC SURVEY DESIGN

COURSE OUTLINE

This course gives practical background for 3D survey design. It also provides the understanding of acquisition geometries, which is necessary for optimal seismic processing.

ABREVIATIONS

This is a list of commonly used abbreviations in this course notes. b bin dimension
Fdom dominant frequency
Fmax maximum frequency
MA migration aperture
NC number of channels
NRL number of receiver lines
NSL number of source lines
NS number of source points per unit area
RI receiver line interval
RLI receiver line interval
SI source interval
SLI source line interval t two-way travel time
Vint interval velocity immediately above the reflecting horizon
Vave average velocity from surface to the reflecting horizon
Xmin largest minimum offset
Xmax maximum recorded offset
Z depth to reflecting horizon

UNITS CONVERSION TABLE

To convert imperial To metric units Multiply by from imperial units

Inches (in) Centimetres (cm) 2.54
Feet (ft) Meters (m) 0.3048
Miles (mi) Kilometres (km) 1.609
Square Miles (m ) Square Kilometres (km ) 2.56
Acres (ac) Hectares (ha) 0.405
Barrels (bbls) Cubic Meters (m ) 0.159
Thousand Cubic Thousand Cubic
Feet Gas (mcf) Meters (10 m ) 0.028169
Pounds (lb.) Kilograms (kg) 0.454

To convert metric To Imperial units Multiply by units Centimetres (cm) Inches (in) 0.3937
Meters (m) Feet (ft) 3.28
Kilometres (km) Miles (mi) 0.6215
Square Kilometres (km2) Square Miles (mi2 ) 0.39
Hectares (ha) Acres (ac) 2.47
Cubic Meters (m3) Barrels (bbls) 6.29
Thousand Cubic Thousand Cubic
Meters (10 m ) Feet Gas (mcf) 35.5
Kilograms (kg) Pounds (lb.) 2.2

3D-SEISMIC SURVEY DESIGN

TARGET DEPTH

The 3D seismic survey should be designed for the main zone of interest (primary target). This zone will determine project economics to the largest degree end therefore should be the one effecting parameter selection for the 3D seismic survey.
Fold, bin size and offset range to be used for stacking, all need to be related to the main target. The direction of major or geological features such as, faults or channels may influence the direction of the Receiver and or Source lines (Fig. 1).

[pic]

Fig. 1. Direction of Receiver and Source lines

The secondary target zones of interest or the regional objectives may have a large influence on the 3D design as well. A shallow second target, for example, may require very short near offsets. Deeper regional objectives may dictate that the far offset of the survey should be substantially greater than the maximum offset for stack, used in the fold calculation at the target level (Fig. 2).
[pic]

Fig. 2. Design the 3D for the primary target horizon, keeping in mind the secondary zones above and below, and any markers needed for mapping.

The largest offset that should be recorded is generally very close to the target depth. Many models and survey data have shown this to be a very good and usually fairly close assumption. Rule of thumb – Xmax should be approximately the same as the primary target depth, usually expressed as Xmax = Z.

SURVEY SIZE

The minimum technical objectives of 3D seismic acquisition and processing are to deliver a fully migrated 3D seismic data volume and to optimise the resolution of the seismic image within it. Seismic data must be migrated to achieve optimum lateral and vertical resolution. In order to avoid edge effects and to ensure correct focusing of the seismic image up to the limit of the seismic image up to the limit of the subsurface target after migration, data acquisition must be extend beyond the subsurface target area by an amount defined by the migration aperture radius. Data must be also being registered for a minimum recording time. The choice of an appropriate migration aperture radius is a sensitive issue because it has a significant economical impact.
For maximum resolution, it is necessary to migrate the 3D seismic data. Post-stack time migration focuses seismic diffractions, relocates seismic events towards their correct positions, and recovers seismic amplitudes to a degree dependent on the migration algorithm. All this operations involve collapsing diffraction hyperbolae.

Definition of Subsurface Target Depth

Before 3D survey design can begin, interpretation objectives need to be clearly specified. The lateral and vertical extent of the complete subsurface target volume can then be estimated. This subsurface target volume should contain all structural achieve the interpretation goals.
The areal extent of the subsurface target is often thought to be reasonably well-known if the subsurface structure has already been mapped using existing 2D seismic data. The maximum extent of the subsurface target volume should be defined. Any uncertainty in the lateral or vertical must be recognised, estimated and included in the dimensions of the subsurface target volume.
The maximum depth of the subsurface target volume is defined by the deepest level of interest at which a fully-migrated 3D seismic image is required. This may be the base of the deepest reservoir interval or the depth of the deepest data critical to the final interpretation.
In order to correctly migrate all the seismic energy which originate from the subsurface target volume. Hence, a migration aperture radius around the target surface area and a minimum recording time needed to register diffraction energy originating from the deepest level of interest, within the subsurface target volume must be defined.
The geometry of the migration aperture radius which will focus dipping energy from the limbs of a diffraction hyperbola observed on a CMP stack is shown on Fig. 17.

[pic]

Fig. 3. Definition of Migration Aperture Radius, L.

The migration aperture radius, L required to collapse a diffraction hyperbola to its apex position is given by

Z0 = VT0/2

L = Z0tanΘ (1)

.

where L - migration aperture, expressed as a horizontal distance. Z0 - depth to the apex of diffraction hyperbolae Θ - angular migration aperture = dip of diffractor element after migration.
This is a very simple formula. It should be noted that Z0 is the depth to the dipping segment of the migration aperture. This is most important.

MINIMUM RECORDING TIME

The minimum recording time is determined from the equation for a diffraction hyperbola on a zero-offset section T2 = T02 + 4X2/Vmig2 (2)

T - seismic two-way time along diffraction hyperbola
T0 - seismic two way time to the apex of the diffraction hyperbola.
X - horizontal offset from apex of diffraction curve to Element at time T.
Vmig- migration velocity required to collapse diffraction curve, and this depends only on the velocity distribution above the diffracting point.

If we substitute X = L = Z0tanΘ from equation (1), then

Tmin2 = To2 (1+tan2Θ) (3)

where
Tmin - seismic two-way time along a diffraction hyperbola
T0 - seismic two-way time to apex of diffraction hyperbola

Θ - angular migration aperture

Tmin = 1.41T0 when Θ = 45 degree (4)

SPECIAL COSIDARETIONS OF 3D VS. 2D

One needs to specify the objectives of a 3D far more precisely than for a 2D survey because the acquisition parameters are much harder to change in mid-program.
With a 3D survey (as opposed to 2D) much more line cutting is required in forested areas and the sand dunes areas. On a 3D survey the equipment stays on the ground much longer time than with 2D.
Spatial sampling requirement are the same for 3D as for 2D. In practice, however, sampling in 3D is usually much
Coarser than in 2D.
The source and receiver lines are laid out over an area and the recording have an azimuthal element that is not present in 2D. 3D migration has a better chance of positioning over the complicated anomalies.

DEFINITION OF 3D TERMS

Figures Fig.4 and Fig.6 show a straight line 3D survey, in plane view, with most of the definitions used in this course.
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Fig.4. 3D Survey Terms

Source Line
A line (perhaps a road) along which source points are taken at regular locations. The in-line separation of sources (source interval, SI) is usually equal to twice the Common Mid Point (CMP) bin dimensions in the x-line direction. The distance between one source line and the next is usually called the Source Line Interval (SLI). The SLI and SI determine the source point density – or how many source points per square kilometre there are.

Receiver Line
A line (perhaps a road) along which receiver are laid out at regular intervals (receiver interval, RI), equal to twice the in-line dimension of the CMP bin. The distance between one receiver line and the next is commonly referred to as the receiver line interval (RLI).

In-Line Direction
Parallel to receiver lines.

X-Line Direction
Orthogonal to receiver lines.

Box (Often called Unit Cell)
In straight line 3D survey this name applies to the area bounded by two adjacent source lines and two adjacent receiver lines (Fig. 18 and Fig. 20). The interesting thing about a box is that the box usually represent the smallest area of the 3D survey that contains the entire survey statistics. In a straight line survey the midpoint bin located at the exact centre of the box will have contributions from many source-receiver pairs, but the shortest offset trace belonging to that bin will be the largest minimum offset of the entire survey.

Patch
A patch refers to all live stations for any source point in the 3D survey. It usually forms a rectangle of several parallel receiver lines. The patch moves around the survey to occupy different template positions.

Template
A template is a combination of a particular receiver patch
Into which a number of source points are recorded. These source points may be inside or outside the patch. Template = Patch + associated Source Points

Swath
Swath has been used with different meaning in the industry. At first, it had the meaning of using parallel and coincident shot and receiver lines. It can now mean a template – or even a series of templates which stretch across the entire width of the survey.

Midpoint
The point located exactly between a source and a receiver location. The midpoints will usually be scattered and may not necessarily from a regular grid (Fig.5).

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Fig.5. 3D Bin Terms

CMP Bin
A small rectangular area. Usually the dimensions of a bin = SI\2 * RI\2. All midpoints that lie inside this area, or bin, are assumed to belong to the same common midpoint and all traces that lie in the same bin will be CMP stacked and therefore contribute to the stacking fold.

Super Bin
This name (and others like macro bin or maxi bin) applies to a group of neighboring CMP bins. These are used for velocity determination, residual static solutions, multiple attenuation, and some noise attenuation alogoriyhms.
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Fig.6. Some additional terms in a perspective view.

Fold

Fold is the number of midpoint being stacked within a CMP bin. The fold varies from bin to bin and for different offsets.

Signal-to-Noise Ratio

The ratio of the energy of the signal over the energe of the noise. Usually abbreviated as S\N.

Source Point Density
The source point density (or sometimes called shot density), NS, is the number of source points\km2 . NS, together with the number of channels, NC, and the size of the CMP bin will completely determine the fold.

Xmin
Xmin is the largest minimum offset in a survey (sometime referred to as LMOS), as described under Box. See Fig.7. A small Xmin is necessary to record shallow events.

[pic] Fig.7. One Box showing Sources, Reseivers, Bins and Xmin
Xmax

Xmax is the maximum continuous recorded offset, which depends on shooting strategy and patch size. Xmax is usually the half-diagonal distance of the patch. A large Xmax is necessary to record deeper events. The range of offsets defined by Xmin and Xmax should be guaranteed in every bin. In asymmetric sampling, the inline maximum offset and the cross-line maximum offset will be different.

Migration Apron (sometimes referred to as
Migration Aperture)
The quality of images achieved by 3D migration is the single most important advantage of 3D vs. 2D. The migration Apron is the width of the fringe area that needs to be added to the 3D survey to allow proper migration of any dipping event. It need not be the same width on all sides of the survey.

Fold Taper
The fold taper is the additional surface area needed to build up full fold. Often there is some overlap between the fold taper and the migration aperture because one can tolerate a somewhat reduced fold on the outer edges of the migration aperture.
Figure 7 will help to understand a few of the terms just discussed. Assuming RLI and SLI of 360 m, RI and SI of 60 m, the bin dimensions are 30 m x 30 m. The box (being formed by two parallel receiver lines and the orthogonal source lines) will have a diagonal of
Xmin = (3602 + 3602)1\2
The value of Xmin will define the largest minimum offset (LMOS) to be recorded in the bin that is in the centre of the box.
Note It is bad practice to make sources and receivers coincident – reciprocal traces do not add to fold.

DEFINITIONS, PARAMETER SELECTION,
DESIGN RULES OF THUMB

3D Survey design depends on so many different input parameters and constraints that it has become quite an art. Laying out lines of sources and receivers must be done with an eye toward the expected results. Some rules of thumb and guidelines are essential to help one through the maze of different parameters that need to be considered. Computer programs are now available to assist the geophysicist in this task.
There are 7 key parameters in any 3D. The following decision sequence is presented for determining Fold, Bin Size, Xmin, Xmax, Migration Aperture, Fold Taper and Record Length. It summarizes the key parameters that need to be determined for 3D design.

STRAIGHT LINE

Generally the source and receiver lines are laid out orthogonal to each other. Such an arrangement is particularly easy for the survey and recording crews. In the Straight Line method example, receiver lines could run East-West and the source lines North-South, as shown on Fig.8a and Fig.8b, or vice versa. Also, the source and receiver lines, can be rotated around the source or receiver lines. This method id easy to lay out in the field and can accommodate extra equipment (lay out ahead of shooting) and roll-along operation.

[pic]

Fig.8a. Straight Line Design

[pic] Fig.8b. Detailed view

All sources between adjacent receiver lines are vibrated, the receiver patch is rolled over one line and the process repeated. A portion of a 3D layout is shown in Fig.8a and detailed view in the Fig.8b.

3D STACKING FOLD

Stacking fold is the number of traces that contribute to one stack trace, i.e. the number of midpoints per CMP bin. Fold is usually based on the desire for good Signal-to-Noise (S/N) ratio. If the fold is doubled, a 41%increase in S/N is accomplished (Fig. 9). Fold should be decided upon by looking at previous surveys in the area (2D or 3D), a careful evaluation of Xmin and Xmax , modelling, and remembering that DMO and 3D Migration can effectively improve the signal to noise ratio.

[pic]

Fig. 9. Fold vs. S/N.

As a rul of thumb, use 3D = 1/2*2D Fold.
For example, 3D Fold = 1/2 * 40 = 20, to achieve comparable results only if the area has excellent S/N and only minor problems with statics as expected. As well, 3D migration will focus the energy batter then migration of 2D data, therefore allowing a reduction in fold. If the 2D trace spacing is much smaller than the 3D fold must be relatively higher to achieve comparable results.
If all offsets are within the acceptable recording range then one can be easily determine the fold with the following formula:

Fold = NS * NC * b2 * U

where NS - number of source points per unit area NC - number of channels B - bin dimension (Here, we are assuming square bins) U - units factor (10-6 for m\km2 0.03587*10-6 For ft/mi2
This is quick way to figure out whether, on the average, the fold is adequate. In order to determine the fold adequacy in a more detailed manner, lets look into the different components at fold. For the purposes of the following examples we will assume that the chosen bin size is small enough to satisfy the aliasing criteria.

IN-LINE FOLD

For A straight line, the inline fold is defined similarly to the fold on 2D data, the formula is as follows.

In-Line Fold = Number of receivers*station interval / (2*source interval along the receiver line) or In-Line Fold = receiver line length / source line interval) = RLL/2*SLI,

since the source line interval defines how many source points there are along any receiver line.
For the time being we assume that all receivers are within the maximum usable offset range.

X-LINE FOLD

The X-Line fold is simply half the number of receiver lines live in the recording patch.

X-Line Fold = NRL/2 , number of receiver lines / 2 or X-Line Fold=shot spread length/(2*receiver line interval)

where (shot spread length) is the maximum positive crossline offset minus the largest negative crossline offset).

TOTAL FOLD

The total fold is noting more than the product of the in-line fold and the X-Line Fold

Total nominal fold=In-Line Fold * X-Line Fold

In the example (Fig. 10a) e.g. total nominal fold=6*5=30
This answer is of course the same as we calculated initially using the formula Fold = NS * NC * b2
NS - Number Source Lines
NC- Number of channels b - bin size [pic]

Fig. 10a. Total fold from 10*72 Patch.
[pic]

Fig. 10b. Total Fold from 9*80 patch.

TOTAL FOLD IN TERMS OF MAXIMUM OFFSET AND LINE SPACING

We can modify the general fold equation and express fold in terms of areas. This gives us an insight in calculating fold for different sizes of receiver patches. In particular, it allows us to calculate the fold for different offset ranges. It has been determined that

In-Line Fold = RLL / (2*SLI)

which is In-Line Fold=(In-Line patch dimension)/(2*SLI)
Similarly X-Line Fold=(X-line patch dimension)/(2*RLI)
Combined to Total Fold=In-line patch fold * x-line patch fold

FOLD TAPER

Another very important factor when calculating fold is the Fold Taper. It describes the area around the full fold area where the fold build up occurs. It is distances need to be calculated separately in the in-line and x-line direction as follows In-Line Taper = (In-Line Fold / 2-0.5)*SLI X-Line Taper = (X-Line Fold / 2-0.5)*RLI
An even better way to express the fold taper is in terms of source and receiver line interval because it is easier to study when looking at fold maps (Fig. 11).

[pic]

Fig. 11. 3D Fold Map.

Hence the term Fold Rate is being defined as the increase in fold in the specified direction.

In-Line Fold Rate=SLI*Total Fold / In-Line Fold Taper X-Line Fold Rate=RLI*Total Fold / X-Line Fold Taper

In the example of the 10*72 patch the tapers and fold rates would be as follows

In-Line Taper=(6 / 2 - 0.5)*360m=900 m X-Line Taper=(5 / 2 - 0.5)*360m=720 m

In-Line Fold Rate=360*30 / 900m=12 per SLI,

which translates into 2.5 line intervals.

X-Line Fold Taper=360m*30fold / 720m=15 per RLI,

which equals to 2 line intervals.

The maximum distance on Receiver and Source lines, where the Fold will reach it’s maximum, can be defined with the following two equations:

MAXDISTRL=((MFRL-1)*SLINT+(FSLST-FGST)*GRINT)/2

MAXDISTSL=((MFSL-1)*RLINT+(FRLST-FVPST)*VPINT)/2

PATCHES AND EDGE MANAGEMENT

The shape of the patch will have a great impact on several attributes of the 3D. The related parameters should be optimized, keeping the survey objectives in mind. A good understanding of Edge Management is critical to delivering a suitable data set for the task at hand.

OFFSET DISTRIBUTION

In Figure 14a is shown the definitions for Offsets and Azimuths. Each CMP bin usually contains the midpoints from many source – receiver pairs. Each trace in a bin has an offset (distance from source to receiver0 and an azimuth (direction or compass angle) from source to receiver. Considering the distribution of these two attributes is of paramount importance for a successful 3D.
Offset distribution in a stacking bin will be most affected by a fold.
[pic]

Figure 12a. Offset and azimuths in a CMP Bin, showing 8 Source-Receiver Pairs Contributing Midpoints to a Centre Bin.

AZIMUTH DISTRIBUTION

Figure 13 shows a method of displaying the azimuths (directions) of each trace which belongs to a CMP bin. Each “spider leg” indicates the offset (length and color of the leg) and points in the direction from source to receiver. The leg length are scaled so that the largest offset in the entire survey would be represented by a leg equal to half the bin height.

[pic]

Fig. 13. Azimuth Distribution – Spider Diagram.

PATCH DIMENSION – 85% RULE

Let us discuss patches with an aspect ratio of 1 (In-line dimension equals X-line dimension).
Consider a circle of area = 1, with a radius of X max (large circle in Figure 14). If the patch lies entirely outside of this circle, then 27% of the channels in the patch are being used to record data that will probably be muted out. On the other hand, one can reduce the patch in size to lie entirely within the recorded offset, as shown by the small square. Xmax is to be measured along the diagonal of the patch but now the patch is only covering 64% of the area of your design objective, i.e., the large circle. This is the other extreme of inefficiency; there are only a few traces which lie at offsets close to your design maximum offset. Using “The 85% Rule” is a good compromise to determine the aspect ratio of the patch to Xmax.[pic]

Fig. 14. Patch Dimension vs Xmax.

The 85% Rule is a simple way to optimize the area of usable traces recorded and the number of channels needed. It works as follows (Fig. 15). 1. Determine Xmax 2. Choose the in-line offset, Xr, to be 0.85*Xmax 3. Choose the x-line offset, Xs, to be 0.85*Xr=0.72*Xmax
[pic]

Fig. 15. Ideal Patch, using the 85% Rule.

For a real example with Xmax = 2000 m
In-line dimension Xr = 85%*Xmax = 1700 m
X-line dimension Xs = 85%*Xr = 1445 m
Aspect ratio Xr/Xs = 85%
The relationship between the different areas from Figure 15 is shown graphically on Figure 16.

[pic]

Fig. 16. Percentage of Area over Reference Area.

PLANNING AND DESIGN

Survey design depends on so many different input parameters and constraints that it has become quite an art. Laying out lines of sources and receivers must be done with an eye toward the expected results.
There are 7 key parameters in any 3D. The following decision table is presented for determining fold, bin size, Xmin, Xmax, migration aperture, fold taper and record length.

FOLD
BIN SIZE
Xmin
Xmax
MIGRATION APERTURE
FOLD TAPER
RECORD LENGTH

AGOCO-QC 3D DESIGN

The main guiding principles for designing of 3D field recording parameters is the “Designing 3D Seismic Surveys”, by Mike Galbraith, Andreas Cordsen and Jhon W. Peirce (1998), which are part of the presented 3D survey design sequence and 3D survey design formulas.
Throughout the 3D design, it is very important, that the field records, processing and interpretation results from 2D seismic data acquisition to be used.

CALCULATION OF THE 3D-SURVEY SIZE

INPUT PARAMETERS - CONC. 80W, O-POOL

Zone of interest Sarir sandstone
Depth of Target 3000 m – 3100 m Structural tops
Two-way Time to Target 1.85 – 1.95 seconds
Average Velocity 3100 m/s
Maximum Frequency 50 Hz
Desired Fold 72
Maximum Dip 6 degrees
Diameter of the smallest Target - 200 m (Faults)

Base Survey Area 10.60 km x 5.80 km = 61.48 Sq. km

Shallow Horizon: Depth-530 m, To-0.546 s,Va–1940 m/s V1 = 2000 m/s, V2 = 2780 m/s

Base Area, depth and dip of the target horizon.

MIGRATION APERTURE AND MIGRATION SHIFT

Calculation of the migration apertures for the four edges of the base area.

Migration shift

Xmig = Z*tan(Q)

Top of base area: Xmig = 2961 * tan(6)=311, use 300 m.
Bottom of base area: Xmig = 2945*tan(6)=309 use 300 m
Right of base area: Xmig = 2992*tan(6)=314, use 300 m
Left of base area: Xmig = 2992*tan(6)=314, use 300 m

Migration aperture after Stack

The migration aperture radius, L required to collapse a diffraction hyperbola to its apex position is given by:

Td = SQRT(X**2+4X**2/Vmig**2);

Z0 = VT0/2 ; X = L = Z0tanΘ; Θ = 45 Degree;
Td = 1.41To

Tm = 1.41 x 1.85 = 2.61 s (Minimum recording time)

Migration aperture for diffraction from the fault zone with
Depth Z = 2830 m and Θ = 30 Degree

L = Z0tan(Θ) L = 2830 x 0.5774 = 1634 m, use 1635 m

Revised area with account for migration.

[pic]

Total Migrated area

Migrated Area = (10.6+0.6)*(5.8+0.3+1.635) = 86.632 Sq. km

SELECTION OF THE LARGEST MINIMUM OFFSET

Depth of the first refracted horizon = 300 m ( H1-80 )

Xmin = 1.2 x 300 = 360 m

The RLI and SLI are largely determined from the required value for the largest minimum offset Xmin.

Xmin = SQRT(RLI**2 x SLI**2)

RLI = SLI = SQRT(Xmin**2 / 2)
RLI = SLI = SQRT(360**2 / 2) = 255 m, use 250 m

SELECTION OF THE X-LINE MAXIMUM OFFSET

Depth of the first shallow horizon - 530 m
Vint ( V1) above the horizon = 2000 m/s
Vint ( V2 ) below the horizon = 2780 m/s

Minimum refracted wave interference - Xm

Xm = 2Zsin( i ) / cos( i - φ ) i = arcsin ( V1 / V2 ) = arcsin( 2000 / 2780) = 46 Degree
Xm = 2 x 530 x sin( 46) / cos(40) = 995 m
The Largest Minimum Offset < 995 m

Depth of the first shallow horizon - 530 m
Vint ( V1) above the horizon = 2000 m/s
Vint ( V2 ) below the horizon = 2780 m/s

Minimum refracted wave interference - Xm

Xm = 2Zsin( i ) / cos( i - φ ) i = arcsin ( V1 / V2 ) = arcsin( 2000 / 2780) = 46 Degree
Xm = 2 x 530 x sin( 46) / cos(40) = 995 m
The Largest Minimum Offset < 995 m

BIN SIZE

Bin size b < Vint/(NxFdom)= 3730/(4 x 40 ) = 23 m where: Vint – interval velocity below main target horizon; N – 2 to 4 points per wavelength of dominant frequency; Fdom – dominant frequency.

RI(Receiver St. Int.)=SI(Source St. Int.)=2b=50 m

MAXIMUM RECEIVER LINE LENGTH – Xmax

Xmax = Main Target Depth = 3000 m
Number of channels per Receiver line
NC/RL = 2 x Xmax / RI = 2 x 3000 / 50 = 120 channels

SURFACE AREA

Surface area to achieve full fold at migration area.

3D Receiver Lines Patch
Number of receiver lines 6
Number of channels per line 80
Receiver Line Interval 350 m
Source Line Interval 350 m
In-Line Receive r Spacing 70 m
In-Line Source Spasing 70 m
[pic]
Fig. 23. Surface 3D-Area
Surface Area=(24.39+2*1.3125)*(8.485+(2*0.4375)=252.86 Sq.km

OPERATIONAL AREA

Slight increasing, due to Line Spacing.
[pic]
Fig. 24. 3D-final surface area.

CALCULATED 3D-AREA PARAMETERS

Base Area Unmigrated Full Fold Requared

24 km * 7.73 km = 185.52 Sq.km

Base Area Migrated Full Fold Recuared

24.39 km * 8.485 km = 206.949 Sq.km

Surface Area to achieve Base Area Migrated fold

27.015 km * 9.36 km = 252.86 Sq.km

Surface Area as per Operational Requirements

27.3 km * 9.45 km = 257.985 km

SEQUENCE OF EVENTS FOR 3D ACQUISITION

Scouting
Design the 3D Survey
Request Regulatory Approvals
Check on Crew Availability
Send Out Bid Request
Sign Legal Contract
Print Land Owners + Community Relations
Check on Local Operating Conditions
Surveying
Uphole Drilling
Testing
Recording
Processing
Interpretation
Drilling

Fig.25. Overall Time Line

-----------------------
9.36 km

27.015 km

257.995 Sq.km

1.3125 km

0.4375 km

Base Migrated area
24.39*8.485=206.949 Sq.km

10600 m

5800 m

Max. Dip = 6 degree

Base area

300 m

300 m

1635 m

300 m