Seismic surveys use seismic waves to image the subsurface. There are two main types: refraction surveys use refracted waves to determine shallow layer velocities, while reflection surveys use reflected waves to image deeper geological structures and boundaries between rock layers. Reflection surveys require more receivers and sources to adequately image the subsurface, making the data acquisition and processing more complex but able to image deeper targets compared to refraction surveys.

1. Introduction
to Seismic
Method:

2. • Measurement of seismic-wave travel time is one of the most
common geophysical method.
• Seismic exploration is divided into refraction and reflection
surveys, depending on whether the predominant portion of
the seismic waves’ travel is horizontal or vertical.
• Refraction seismic surveys are used in engineering geophysics
and petroleum exploration.
• Seismic reflection surveys, on the other hand, detect
boundaries between different kinds of rocks; this detection
assists in the mapping of geological structures.
• Seismic energy is detected on land by using devices called
geophones, which react to on-site ground motions.
SEISMIC METHOD

3. SEISMIC SURVEY
• OBJECTIVES
• PREPARATION & PLANNING
• PARAMETER SELECTION
• INSTRUMENTS
• FIELD OPERATION

4. OBJECTIVES
REGIONAL EXPLORATORY INVESTIGATIONS
• Delineation of structural and stratigraphic anomalies
FIELD DEVELOPMENT
• To mark suitable locations for field development and for reservoir
studies
PROSPECT DELINEATION
• To mark the depth of prospective horizon and trap
closures

5. PREPARATION
AVAILABLE BUDGET & TIME
AVAILABLE DATA
Geological Data
Geophysical Data
Other Information

6. PLANNING & DESIGNING
1. ACQUISITION PARAMETERS
2. BID INVITATION
a. Minimum Offset b. Maximum Offset
c. Source Interval
e. No. of Channels
d. Receiver Interval
g. Source (Dynamite or Vibroseis)

7. RECEIVER AND SOURCE PARAMETER SELECTION
• SPREAD TYPE
• RECEIVER LAYOUT
• SOURCE TYPE

8. INSTRUMENT FOR SEISMIC SURVEYING
1. Geophone.
2. Seismic Cable.
3. Seismograph.
4. Energy Source.
5. Seismic Crew.

9. Weight drop
Dynamite
SOURCE TYPE
Vibroseis
Hammer

10. DYNAMITE
• SHOT HOLE DEPTH
• CHARGE SIZE
• SHOT POINT INTERVAL
• NUMBER OF HOLES
• SOURCE ARRAY PATTERN
SP Interval
Hole Depth
Charge Size
PARAMETERS:

11. •The blast of explosives produces a very
strong energy,
•Placing of the explosives to the bottom of
a hole from 1 to 35 meters,)and the energy
is better distributed.
•In order to make the holes, a hammer
perforator, an auger or drilling rig is used.
•In the sand, a simple metallic tube is very
efficient.
•In some desert regions, where the drilling
is impossible, explosives can be suspended
and exploded in the air about 1.5 m from
the ground
•This method, very noisy & dangerous

12. VIBROSEIS

17. FIELD PROCEDURE
• Planting geophone along a straight line and detonating.
• Generating seismic waves by detonating explosives on one end of a line.
• Recording seismograph.
• Picking 1st arrivals.
• plotting of data to determine V1V2h1

18. Trimble Man Pack - 4700 GPS
• GPS used by the Survey Crew
for locating the Source & Receiver
Points of the Seismic lines, carried
on their shoulders
External Batteries and Receiver
• Its is connected with two external
batteries and a receiver which receives
the signal from the satellite.

19. Shot Points Receiver Points
• After locating the points, the crew mark the places of source
and receiver points finally marking a seismic line
Source Points with red paint Receiver Points with white paint

20. Drilling Jackhammer
• Drilling Crew uses Jackhammers
for shallow holes
Man Portable Drilling Rig
• For deep holes, Man Portable
Drilling Rigs are used

21. Dynamite Stick for Deep Shots
• After drilling shot holes dynamite is
loaded in them, using dynamite sticks
Detonator
• Detonators are placed in the dynamite
stick, used to initiate the blasting of
dynamite

22. • Lowering of Charge in a Drilled Hole
with detonator in them
• Hole is loaded and filled with Sand
• Loading is done and place is marked

23. Geophone Stings
Takeout Point of a Takeout Cable
• This crew first of all layout the
Geophones on the seismic lines
as spread.
• These geophones are connected
to each other by the Takeout Cable

24. CABLE & GEOPHONE
Link cableGeophone string

25. LAYOUT(FRONT CREW)

26. CABLE LAYOUT

27. GEOPHONE PLANTATION

28. ROAD CROSSING

29. LINE
SOURCE
RECEIVER

30. Station Unit Box
• Takeout cable is then connected to
Station Unit Box
Crossing Station Unit Box
• All the Station Unit Box is further
connected with one Crossing Station
Unit Box (of an array)
• Then yellow cable called Jumper Cable
is finally connected to Recording Truck
through which all the information goes
into it

31. RECORDER

32. CABLE PLUG IN THE RECORDER
FROM SPREAD

33. Color Line Monitor
Recorder
Tape Driver
• Monitor on which the Observer control
all the activities on a seismic line
• The recorder which records all the data
coming through cables
• The tape driver records all the data
on the magnetic tapes or cartridges

34. Camera
Seismic Source Synchronizer
• The thermal plotter used to make a hard
copy of the recorded data
• Device which synchronizes the blaster.
Before shooting, recorder presses ARM
button to charge the detonators, at the
same time the blaster operator presses
the ARM button in the blaster
• Then recorder presses GO button to
blast the dynamite

35. Portable recording system
SEISOMOGRAPH

36. Blaster
• Bag carried by the shooting crew is called
The Blaster, it works in coordination with
the Seismic Source Synchronizer
• “Blast view” on seismic
line

37. A recorded result of shot point after the blast
SEISOMOGRAM

38. A recorded result of shot point after the blast
SEISOMOGRAM

39. • After all the shots are recorded every thing is wounded
• The data is send to the Operator Company
• The place is restored by the Green Team and inspected by
the Client Company
• Then Operator Company sends data to DGPC

46. SPREAD GEOMETRY
The most common recording type consists to send seismic
waves from one shot point and to record reflected waves
with many (48, 96 or more) geophones regularly disposed
on the ground along a seismic cable.
The CDP is the reflection point in depth, then CMP is the
midpoint on the ground between shot and a geophone.
With a switch (roll-along switch), the observer can
"displaces" the recording geophones along the line with a
constant number of actives geophones (24, 48 or more).
The aim of this process is to add the travels having a
reflective common point, in order to improve the signal /
noise ratio. With 48 active geophones, there are 24 travels
adding on a common reflector (Fold 24).

47. Basic Spreads

49. The shot or the vibration point can be situated:
• At the extremity of the active geophones (End shot)
• At the center of the geophones. (Split spread shot)
• At a certain distance (offset) of first geophone
The last geometry allows to have a long distance of offset,
The second is more adapted if the reflectors are tilted.

59. NOISE
Noise is the information on the seismic
record which one does not wish to use.
TYPES OF NOISE:
1. Random Noise or Incoherent Noise
2. Coherent Noise

60. RANDOM NOISE OR IN COHERENT NOISE
It is the seismic energy that does not align up from trace to
trace or record to record on seismic record It displays no
systematic pattern.
This noise is uncorrectable.
We can overcome random noises by recording more than
one traces from the same location.
Sources of Random Noise:
i. Wind Noise
ii. Water Flow Noise
iii. Small Movement With in the Earth
iv. Local Noise
v. Bad Geophone Noise

61. COHERENT NOISE
It is seismic energy which aligns from trace to trace or record to record on
seismic record.
• Often, it is very similar to the signal and usually more difficult to
overcome than the incoherent/random noise.
• By examining the patterns of coherent noise, we can
devise field procedures to reduce it.
Source size and source depth , Electric Filtering, Receiver Arrays,
Source Arrays, Deconvolution and Editing and Muting.
Sources Of Coherent Noise:
i. Multiple Reflections
ii. Direct Arrivals and Refracted Waves
iii. Diffraction Events
iv. Ground Roll

63. • Head waves are always the first events seen on a record.
• They are linear and often very visible and strong.
• Sometimes they can disappear with large offset.
• Many geophysicists try to remove head wave using
•surgical mute,
•FK filtering
•adapted NMO stretch mute value,
• but in some case, uppermost reflection and refraction
can be very close and difficult to distinguish.

64. Refracted Waves
In Seismic reflection survey the refracted events
comes as first arrival.

65. Ground Roll
Ground rolls are Rayleigh waves which
appear as second arrival on seismic section.

66. • Surface waves (Rayleigh, Love) primarily Rayleigh
are
– low velocity,
– low frequency signal,
– With relatively higher amplitude seen below shots.
They override the useful reflections.
• They can be reduced using
– frequency filtering
– FK filtering.

67. Diffracted Events
At faults and some unconformities diffracted waves
are generated on seismic section.

70. • The seismic reflection takes an interest essentially to the P compression
waves, in the setting of seismic studies for the geo-technical;
• the recording of the S waves can to prove out to be useful for the
shearing modules calculation.
• In knowing the velocity of the P waves and S, it is possible of calculating
the Poisson’s ratio:

71. Refraction Methods
Advantages Disadvantages
Refraction observations generally
employ fewer source and receiver
locations and are thus relatively
cheap to acquire.
Little processing is done on refraction
observations with the exception of
filtering to help in the process of
picking the arrival times of the
initial ground motion.
Because such a small portion of the
recorded ground motion is used,
developing models and
interpretations is no more difficult
than our previous efforts with
other geophysical surveys.
Refraction seismic observations require
relatively large source-receiver offsets
(distances between the source and
where the ground motion is recorded,
the receiver).
Refraction seismic only works if the speed at
which motions propagate through the
Earth increases with depth.
Refraction seismic observations are generally
interpreted in terms of layers. These
layers can have dip and topography.
Refraction seismic observations only use the
arrival time of the initial ground motion
at different distances from the source
(i.e., offsets).
A model for the subsurface is constructed by
attempting to reproduce the observed
arrival times.

72. Refraction Survey
Advantages
– Amplitude of refractor are large.
– Best for exploration of shallow structures.
– Easy to process and interpret.
Disadvantages
– Exploration for deeper structures is difficult because of large XCrit distance,
– Blind to low velocity layers.

73. Reflection Methods
Advantages Disadvantages
Reflection seismic observations are
collected at small source-receiver
offsets.
Reflection seismic methods can work
no matter how the speed at which
motions propagate through the
Earth varies with depth.
Reflection seismic observations can be
more readily interpreted in terms
of complex geology.
Reflection seismic observations use the
entire reflected wave field (i.e., the
time-history of ground motion at
different distances between the
source and the receiver).
The subsurface is directly imaged from
the acquired observations
Because many source and receiver locations must
be used to produce meaningful images of the
Earth's subsurface, reflection seismic
observations can be expensive to acquire.
Reflection seismic processing can be very
computer intensive, requiring sophisticated
computer hardware and a relatively high-
level of expertise. Thus, the processing of
reflection seismic observations is relatively
expensive.
Because of the overwhelming amount of data
collected, the possible complications imposed
by the propagation of ground motion through
a complex earth, and the complications
imposed by some of the necessary
simplifications required by the data
processing schemes, interpretations of the
reflection seismic observations require more
sophistication and knowledge of the process.

74. Seismic Reflection Survey
Advantages
– Geophone spread needed is relatively shorter.
– Not blind to low velocity layers. Since acoustic impedance exist for
every layer.
– Convenient for deeper exploration.
Disadvantages
– Difficulty in recognizing reflected waves.
– Small amplitude.
– Obscured by overlapping refracted and surface waves.