Seismic method basic

1. SEISMIC SURVEY
P.NAGARAJAN
CENTER FOR GEOTECHNOLOGY

2. 1. Measurement of seismic-wave travel time is one of the most common
geophysical method.
2. Seismic exploration is divided into refraction and reflection surveys,
depending on whether the predominant portion of the seismic waves'
travel is horizontal or vertical.
3. Refraction seismic surveys are used in engineering geophysics and
petroleum exploration.
4. Seismic reflection surveys, on the other hand, detect boundaries
between different kinds of rocks; this detection assists in the mapping of
geological structures.
5. Seismic energy is detected on land by using devices called geophones,
which react to on-site ground motions.
6. On 4 April 1921, Mintrop founded the company Seismos Gesellschaft in
order to carry out seismic refraction surveys in the search for salt domes
acting as trap structures for hydrocarbons

3. Wave Propagation & Basic Principles
of Seismic Wave

5. Basic Principle
• Huygen’s principle
All points on a wavefront can be regarded as point Sources for
the production of new spherical waves; the new Wavefront is the
tangential surface (or envelope) of the secondary wavelets.
• Fermat’s principle
Its states that, of the many possible paths between two points
A and B, the seismic ray follows the path that gives the shortest travel
time between the points.

6. Law of reflection using huygen principle
Sin i=Sin r

7. Law refraction using huygen principle

8. Zoepritz
Equation

9. Seismic Methods
Reflection Method Refraction Method

10. Seismic Data Acquisition Systems

11. Sources On land On water
Impact
Sledge hammer
Drop-weight
Accelerated weight
Impulsive Dynamite
Detonating cord
Airgun
Shotgun
Borehole sparker
Airgun Pinger
Gas gun Boomer
Sleeve gun Sparker
Water gun Steam gun
Vibrator Vibroseis
Vibrator plate
Rayleigh wave
generator
Multipulse
Geochirp
Seismic Sources

12. Energy sources
Dynamite
Hammer
Drop weight
Air gun
Thumber truck

13. SENSOR
Geophone
• Electromagnetic Induction
• Ground motion
• Direction Sensitive
Hydrophone
• Piezoelectric effect
• Pressure variations
• Direction insensitive

14. Survey Geometry For
Seismic Method
2D & 3D

15. Grouping of Geophones and Shot Points

16. 16
S.No Parameters Geometry
1 Bin Size (m) 10X10
2 Receiver interval (m) 20
3 Shot Interval (m) 20
4 Receiver Line Interval (m) 360
5 Shot Line Interval (m) 320
6 Number of Receiver Lines 12
7 Number of Receivers per Line 320(160+160)
8 Total Active Channels 3840
9 Number of Shots per Salvo 108
10 Total Fold (Inline Fold X cross line Fold) 60 (10X6)
11 Aspect Ratio 0.62
12 Geometry Spread Type Sym.split spread
13 Total Shots 24925

17. 17
S.No Parameters Geometry
14 Min. Min Offset (m) 14
15 Spread length (m) 3200 + 3200
16 Max. Max offset (m) 4413
17 0-500 m 1-4
18 500-1000 m 1-8
19 1000-2000 m 13-23
20 2000-3000 m 19-27
21 3000-4000 m 8-18
22 4000-5000 m 0-2
23 1000-3500 m ( ZOI ) 45-54
24 Unique fold (20 m) 36-58
25 Minimum no channels required 3840/108 Shots
26 Total Swaths 8
27 Area 100 SKM

18. Instrument Parameters

19. 19

21. 21
320(160+160)_12LINES_RLI360_SLI_320_108 SHOTS PER SALVO_60FOLD_24925 _SHOTS_ASPR 0.62

22. Common Depth Point
• In multichannel seismic
acquisition where beds do not
dip, the common reflection
point at depth on a reflector, or
the halfway point when a wave
travels from a source to a
reflector to a receiver. In the
case of flat layers, the common
depth point is vertically below
the common midpoint.

23. Fold
•Fold is number of times recorder at one
place
•The number of traces in a CDP gather is
referred to as the fold

24. Data Acquisition
(Outline)

25. • About the work area
• Geology if the area
• Uphole survey
To understand near surface properties and behaviour to know
the weathering layer thickness to get the weathering and sub
weathering velocities to understand any low velocity layers are
embedded in between high velocity layers
• Near Surface Model (NSM)
M
SL
m/s
uphole
Receiver statics
∆tc (-ve)

26. 1. Reflection Method 2D & 3D

28. 2. Refraction Method

30. What is traces
• A seismic trace refers to the recorded curve from a single seismograph
when measuring ground movement

32. Recording Formats
Shell Processing
Support

33. H Source of Geodetic Data= Advance Positioning's SEISURV System
H Origin: Latitude= 27-50
H Origin: Longitude= 99-00
H Origin: False Easting(ft)= 2000000.00
H Origin: False Northing(ft)= 0.00
H Parallel (Latitude)= 29-20
H Scale Ratio= 1: 7300
H R (reduction in ft/1000)= 0.136800
H Standard Parallels (deg-min)= 28-23 & 30-17
H Origin of Longitude= Greenwich
H FEET are the units used for the following grid coordinates and elevations.
H26 SPS HEADER
H26 DEFINITION OF FIELD COLS FORMAT UNITS
H26
H26 LINE NAME 2-17 4A4 -
H26 POINT NUMBER 18-25 2A4 -
H26 POINT INDEX 26-26 I1 -
H26 POINT CODE 27-28 A2 -
H26 STATIC CORRECTION 29-32 I4 MSEC
H26 POINT DEPTH 33-36 F4.1 METRE
H26 SEISMIC DATUM 37-40 I4 METRE
H26 UPHOLE TIME 41-42 I2 MSEC
H26 WATER DEPTH 43-46 F4.1 METRE
H26 MAP GRID EASTING 47-55 F9.1 -
H26 MAP GRID NORTHING 56-65 F10.1 -
H26 SURFACE ELEVATION 66-71 F6.1 METRE
H26 DAY OF YEAR 72-74 I3 -
H26 TIME hhmmss 75-80 3I2 -
H26
H26 1 2 3 4 5 6 7 8
H2645678901234567890123456789012345678901234567890123456789012345678901234567890
Rhollow 10011R1 2646429.0 471024.0 133.0326090000
Rhollow 10021R1 2646272.0 471178.0 134.0326090000
Rhollow 10031R1 2646115.0 471332.0 135.0326090000
Rhollow 10041R1 2645958.0 471486.0 137.0326090000
Rhollow 10051R1 2645801.0 471640.0 139.0326090000
Shell
Processing
Support
(SPS)
Shot/Receiver
file
example
Data Block
Location of information in
the data block
referenced by column
numbers
General Header
Information
SPS

34. H26 SPS-HEADER
H26 DEFINITION OF FIELD COLS FORMAT
H26
H26 FIELD TAPE NUMBER 2-7 3A2
H26 FIELD RECORD NUMBER 8-11 I4
H26 FIELD RECORD INCREMENT 12-12 I1
H26 INSTRUMENT CODE 13-13 A1
H26 LINE NAME (SOURCE) 14-29 4A4
H26 POINT NUMBER (SOURCE) 30-37 2A4
H26 POINT INDEX (SOURCE) 38-38 I1
H26 FROM CHANNEL 39-42 I4
H26 TO CHANNEL 43-46 I4
H26 CHANNEL INCREMENT 47-47 I1
H26 LINE NAME (RECEIVER) 48-63 4A4
H26 FROM RECEIVER 64-71 2A4
H26 TO RECEIVER 72-79 2A4
H26 RECEIVER INCREMENT 80-80 I1
H26
H26 1 2 3 4 5 6 7 8
H2645678901234567890123456789012345678901234567890123456789012345678901234567890
X 1 111 hollow 7051 1 601 hollow 1001 10601
X 1 111 hollow 7051 61 1201 hollow 2001 20601
X 1 111 hollow 7051 121 1801 hollow 3001 30601
X 1 111 hollow 7051 181 2401 hollow 4001 40601
X 1 111 hollow 7051 241 3001 hollow 5001 50601
X 1 111 hollow 7051 301 3601 hollow 6001 60601
X 1 111 hollow 7051 361 4201 hollow 7001 70601
X 1 111 hollow 7051 421 4801 hollow 8001 80601
X 1 611 hollow 7101 1 601 hollow 1001 10601
X 1 611 hollow 7101 61 1201 hollow 2001 20601
X 1 611 hollow 7101 121 1801 hollow 3001 30601
X 1 611 hollow 7101 181 2401 hollow 4001 40601
X 1 611 hollow 7101 241 3001 hollow 5001 50601
X 1 611 hollow 7101 301 3601 hollow 6001 60601
X 1 611 hollow 7101 361 4201 hollow 7001 70601
X 1 611 hollow 7101 421 4801 hollow 8001 80601
X 1 711 hollow 7111 1 601 hollow 1001 10601
X 1 711 hollow 7111 61 1201 hollow 2001 20601
X 1 711 hollow 7111 121 1801 hollow 3001 30601
Field File No.
Source station no.
This channel range comes
from
this set of receivers
corresponds to -
SPS
Relationship
file
example
Data Block
SPS

35. 35
SPS