méthode electrique et methode magnétique dans la prospection géophysique.ppt

une explication simple des deux méthodes electrique et magnétique qui sont utilisées dans la prospection géophysique et la prospection pétrolière.

1. Electromagnetic Surveying Methods

2. 10
-1
300 m30 km

3. http://ece.uprm.edu/~pol/waves_review.pdf

4. Skin Depth

8. Lenz's Law
•When an emf is generated by a change in magnetic flux according to
Faraday's Law, the polarity of the induced emf is such that it produces a
current whose magnetic field opposes the change which produces it.

9. Ampere's &
Biot-SavartLaws
.
×

10. Amperes Law

11. Frequency Domain:
Two approaches to EM Surveying
Time Domain:

18. Time Domain Primary Field
Induced voltage in air and ground

19. Time Domain Secondary Magnetic Field

20. “Smoke Ring”Eddy Current simultaneously
expands and travels downward into the earth
Its rate of travel is proportional to earth resistivity

27. DIGHEM

28. DIGHEM

29. Airborne EM Resistivity

30. DIGHEM-VRES
•The DIGHEM-VRES is a 5-coplanar system with frequencies of 380 Hz, 1400 Hz, 6200
Hz, 25,000 Hz, and 101 000 Hz (the highest HEM frequency commercially available!). It
is a system designed to provide the optimum conductivity mapping range and resolution
for horizontally layered geology. With a full 7.9 m coil separation on all frequencies it is
the optimum system for geologic mapping and many environmental and engineering type
problems.
•

32. RESOLVE -The World's Most Advanced HEM System

33. Airborne EM systems developed by the
Centre are deployed on Skyvan aircraft
operated by Fugro Airborne Surveys.
A "bird" containing receiver coils being
deployed for a survey.

34. TEMPEST-Digital Time Domain
Electromagnetics
•TEMPESTs fixed wing configuration makes it cost
effective for large scale reconnaissance projects, where
ground and helicopter EM surveys would be prohibitively
expensive. The quality detail and accuracy of TEMPEST
data reveals geological and structural information that
cannot be matched by other airborne techniques.

35. TEMPEST
Base frequency 25 Hz
Transmitter area 186 m
2
Transmitter turns 1
Waveform Square
Duty cycle 50%
Transmitter pulse width 10 ms
Transmitter off-time 10 ms
Peak current 300 A
Peak moment 55,800 Am
2
Average moment 27,900 Am
2
Sample rate 75 kHz
Sample interval 13 microseconds
Samples per half-cycle 1500
System bandwidth 25 Hz to 37.5 kHz
Flying Height 120 m (subject to safety considerations)
EM sensor Towed bird with 3 component dB/dt coils
Tx-Rx horizontal separation 122 m (nominal, actual value determined)
Tx-Rx vertical separation 37 m (nominal, actual value determined)
Stacked data output interval 200 ms (~12 m)
Number of output windows 15
Window centre times 15 windows from 13 microseconds to 16.2 milliseconds
Magnetometer Stinger-mounted cesium vapour
Compensation Fully digital
Magnetometer output interval 200 ms (~12m)
Magnetometer Resolution 0.001nT
Typical noise level 0.1 nT
GPS Cycle Rate 1 second

36. HeliGEOTEM
EM system Specifications
Dipole Moment: 230,000Am2
Waveform Frequency: 30 Hz / 4 ms
Waveform: Half Sine
Receiver: GEOTEM® Multi-Component
Fugro Airborne Surveys offers
the HeliGEOTEM™ System,
incorporating the proven
characteristics of the GEOTEM®
system.

38. GEOTEM
•Fugro Airborne Surveys operates three GEOTEM aircraft out of bases in Perth, Australia and
Ottawa, Canada. However, these systems have operated on five continents, in just about every
climate and geological/geographical environment. Survey targets have ranged from mineral
deposits and petroleum reservoirs to groundwater resources.
.
•Measurement in the receiver bird of
three orthogonal components of the
secondary EM field (two horizontal
directions and one vertical).
Recording of both B-field and dB/dT
response data.
•Lower transmitted waveform
frequencies of 12.5, 15, 25, and 30
hertz.
•Measurements during the on-time as
well as the off-time of the transmitter
pulse.

39. MEGATEM
•MEGATEM System Specifications
A time-domain airborne EM system to meet the challenge of
exploration areas located at high altitude, in remote areas, or
requiring deep target detection.

40. MEGATEM & GEOTEM
•Time domain systems

41. Airborne Electromagnetic:
Manufacturer Fugro Airborne Surveys
Model MEGATEM
Waveform frequency 30 or 25 Hz 90 or 75 Hz
Pulse width 4 ms 2 ms
Loop 4 turns 4 turns
Loop area 406 m
2
406 m
2
Dipole moment (approx.) 1.08 x 10
6
Am
2
0.97 x 10 Am
2
Peak transmitter current 665 amperes 595 amperes
Model MEGATEM
II
Waveform frequency 30 or 25 Hz 90 or 75 Hz
Pulse width 4 ms 2 ms
Loop 4 turns 5 turns
Loop area 406 m
2
406 m
2
Dipole moment (approx.) 2.18 x 10
6
Am
2
1.71 x 10
6
Am
2
Peak transmitter current 1340 amperes 840 amperes
1/2 Waveform sampling rate 384 per pulse 128 per pulse
Prestack ("stream") data sampling rate 192 per pulse 64 per pulse
Receiver 3-component induction coil sensor
Measured response voltage (dB/dt) and B-field
Bandwidth base frequency to 10 kHz
Stacking rate 4 stacks per second
Digital recording all raw data channels
Magnetometer:

43. MEGATEM
Specifications
Survey Platform:
Aircraft: CASA 212-200
Transmitter:
Coil axis:
Waveform:
Waveform frequencies:
Pulse width (delta T):
Tx loop dipole moment:
vertical
alternating half-sine-wave current
pulse
25, 30, 75, 90, 125, 150 Hz
1 to 8 milliseconds
up to 6.9 x 10
5
Am
2
Receiver:
Coil axis:
Digitising:
Samples per second:
Gate Distribution:
Off-time:
Recorded data:
3 orthogonal (2 horizontal, 1 vertical)
16 bit at up to 80 kHz/channel
4
standard 20 programmable
up to 36 milliseconds
B-field and dB/dt

44. DIGHEM
Overburden mapping for pipeline
construction

45. Overburden mapping for pipeline
construction
DIGHEM

46. •DIGHEM

50. Airborne EM Resistivity

51. Airborne EM Resistivity

52. Magnetotellurics Method

53. Skin-depth

54. http://hendrix.uoregon.edu/
~dlivelyb/LPE_talk/mt_sour
ces.jpg

55. http://hendrix.uoregon.edu/~dliv
elyb/LPE_talk/mt_sources.jpg

56. http://hendrix.uoregon.edu/~dlivelyb/LPE_talk/mt_xformer.gif

58. Impedance:

63. Ground-Probing Radar (GPR)

64. 0.5-meter antenna separation (offset)

65. Low-freq. antenna, 100 MHzMed.-freq. antenna, 500 MHz

66. High-freq. antenna, 1.0 GHz

67. Pure Profiling
Pure Sounding

70. Electromagnetic wave velocity in meters per nanosecond

72. Cross-hole radar

73. Cross-hole radar

74. Cross-hole radar

75. Diffraction from a Void

80. Strong Impedance Mismatch at the Ground Surface