C:\fake path\3 d cdp curvey

UNDER THE GUIDANCE OF:

Dr. S.S.Teotia

(chairman of Department)

PRESENTED BY:Deepak kumarGp- 11M. Tech. (2nd year)

The geometry applies to points in a straight line.

The reflecting horizons have no dip.

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Most important field techniques is Common Mid Point shooting, often called Common Depth Point (CDP)

Reflections are received several times from under the same mid point using different ray paths

During processing corrections are made for the time difference from one path to another and traces are summed (stacked )

CDP technique implemented by methods according to the objective of the survey

The CDP shooting provides multi-fold data and effectively attenuates

multiple reflections after stacking. These are 2D, 3D, and 4D. In 2D acquisition, In 2D source and receivers

are positioned in a single line. 3D shooting places receivers in area pattern. 4D is time lapsed 3D

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Basic Concepts In 3-D Surveys

There are some new aspects of the survey design in three dimensions relative to 2-D surveys. The 2-D surveys are as linear as the terrain allows.

Source and receiver are normally in-line with each other. The source interval of a 2-D survey must be extended to include a definition of the source line. For 3-D surveys, source line must be defined, since for most

common designs, the source line is orthogonal to the receiver lines.(ii) The receiver line becomes the receiver lines. As many receiver lines are

laid out as the equipment for acquisition allows. Also, the receiver, layout may not be lines but circles, checkerboards and other patterns developed for 3-D

surveys. The analysis of 2-D designs centers on the subsurface coverage in the form of

common-depth points (CDP). For 3-D surveys, the CDP becomes two-dimensional and is termed a "bin". These bins may be square or rectangular and define the spatial resolution of the data sampling. Indeed, deciding the bin size

will be the first step in designing a 3-D template. Subsurface sampling will be, as with the CDP, half the surface size.

3-D Survey layout

Direction : Two types of directions have to be

consider : In- line direction : It is the direction which is

parallel to receiver lines. Sampling in this direction is generally satisfactory.

Cross- line direction : It is direction which is

orthogonal to receiver lines. Sampling in this direction is generally weak and has to be investigated carefully.

Box : the area bounded by two adjacent lines

( spaced RLI ) and two adjacent source lines ( spaced SLI ) Box area = RLI * SLI

Patch : a Patch refers to all live receiver stations that record data form a given source point in the 3-D servey. Patch usually forms a rectangle of several parallel receiver lines.

Template : a particular receiver patch into which a number of source points are recorded. These source points may inside or outside the patch.

Template = patch + associated source points

3-D Survey edge Management

Bin : A small rectangular area that usually has the dimensions (SI/2) * (RI/2). All traces that lie in the same bin will be CMP stacked and contribute to the fold of that bin.

Fold : This is the number field traces that contribute to one stack, the number of midpoints per CMP bin.

fold =

SI

RIN

*2

*

Inline fold=(no. of receivers*Ri)/(2*SLI)

Cross fold=(no. of rec. lines*RLI) /(2*RLI)

Total fold=inline fold*cross fold

Fold tapper:- the width of additional area that needs to be added to the 3-D subsurface area to build up a full fold.

Inline fold tapper=(in-line fold/2 -0.5)*SLI

Cross line fold tapper=(cross line fold/2 -0.5)*RLISwath:-when the template moves in one direction

and reach the edge of the survey area , it will generate a path

Salvo:-it is the no. of fired shots before template moves along the survey

Geophysical Services, ChennaiGeophysical Services, Chennai 1919September 14, 2008September 14, 2008

Shot Line

Receiver Layout

Field LayoutField Layout

Receivers Interval 40m Receiver Line Interval 240 mReceiver Lines 6 Total Receivers 864SL Interval 360m Source Interval 80m

Receiver Shot Point

40 m 80 m

240 m

360 m

3-D imaging of geological featureRegular close data volume Improved resolutionGeneration of view in any directionProvide good quality of data for

structural and stratigraphic interpretation

Edwin S. Robinson:”Basic Exploration Geophysics”.

Milton B.Dobrin:”Introduction to Geophysical Prospecting”.

Robert J. Lillie :”Whole Earth Geophysics”. Keary Brooks:”Introduction to Geophysical

Exploration”. Telferd Etal:” Ap Geophysics”

Andreas Cordsen.”Planning of Land 3-D seismic survey”.