KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 1
1) Estimate the attenuation of the EM fields in the air where σ = 0, μ=μ0 =
4π*10-7 H/m, ε =ε0 =8.85*10-12 F/m, ω= 2*10 4 HZ.
2) Estimate the attenuation of the EM waves through medium of low and high
conductivity ? ε = 10ε0, μ=μ0, σ = 10-3 S/M, 107 S/M , ω= 2*10 4 HZ.
3) Estimate the attenuation factor according to the following data:
Frequency (Hz)
103
103
103
103
103
10
102
104
106
Resistivity ρ (Ωm)
10-4
10-2
1
102
104
10
10
10
10
the attenuation factor of the EM waves is given by :
|Hy /H0| = EXP2*10-3 Z√f/ρ
|Hy /H0| for Z= 30m|
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 2
Estimate the variation of the skin depth with frequency and Resistivity?
Frequency
(Hz)
10-3
10-2
10-1
1
10
102
103
104
106
108
Z=500(ρ/f)
ρ =10-4
ρ =10-3
ρ =10
ρ =103
ρ =104
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 3
Plot the amplitude of the secondary EM field versus time in msec. From the graph
classified the earth material according to its conductivity?
Time
0.5
1.25
1.75
2
2.5
3.25
5
5.8
Amplitude
Time
0.5
0.8
1.25
1.8
2.2
2.8
3.5
4.2
5
Amplitude
Time
1
1.2
1.8
2.1
2.8
3.4
4.2
5.1
6
7.1
8.9
10.2
11.8
13.2
15.8
Amplitude
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 4
Calculate the attenuation factor and the depth of penetration of the following material
for the two regimes, namely, the inductive and radar regime.
material
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 5
1) Calculate the apparent conductivity for a layer of thickness 3m and
conductivity 15 mS/m over a lower layer with conductivity 100 mS/m.
2) In an EM31 survey you record an apparent conductivity of 35 mS/m. From
DC Resistivity work, you know that the near surface conductivity is 60 mS/m,
and from a borehole you know that the near surface layer is 2 thick, calculate
the conductivity of layer 2.
3) Calculate the apparent conductivity readings that will be measured at points A,
B, and C over the gravel deposit shown below.
A
B
C
1m
gravel
3m
Till
σ = 10mS/m
5m
σ = 1mS/m
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 6
1) Compute the induction number B and skin depth δ according to the following
data that are listed in the table below. From the calculation, show how the
variation in frequency will affect on the induction number.
Tx-Rx
separation
(m)
3.66
10
20
40
σ=10Ωm
σ=100Ωm
Frequency
Hz
9800
6400
1600
400
2) Calculate the EM31 apparent conductivities that would be measured across the
buried
river
valley
shown
in
the
following
figure.
Till σ=10mS/m
Shale σ=50mS/m
A
B
C
8m
5m
1m
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 7
Evaluate the possibility that the EM31 will be able to detect high conductivity
transport zone with depth to top of 30 ft. evaluate only for a vertical dipole model?
20 ft
σ = 4 mmhos/m
10 ft
σ=100 mmhos/m
30 ft
σ = 4 mmhos/m
σ = 10 mmhos/m
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 8
1) Calculate the radar wave velocity through dry sand and compare this to the
seismic P-wave velocity for dry sand. ( ε = 3-10)
2) Calculate the
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 3
1) the relative response function Φ represents the contribution of the single or
several layers to the overall ground conductivity. It is given by :
Calculate the relative response function Φ for the vertical and horizontal dipole, Φ
Φ following table:
Z = 0.1, 0.2, 0.3, 0.4,
3. Plot z values vesus the
vertical and horizontal dipole, Φ Φ .From the graph compare between them
regarding their sensitivity.
2) the accumulative relative response RV (Z) represent the contribution to the the
secondary magnetic field HS from the material below a normalized depth Z
and is given by
How would you express the area between Z1 and Z2 under the response
relative function in terms of cumulative response function?
4) Calculate the EM31 apparent conductivities that would be measured across the
buried
river
valley
shown
in
the
following
figure.
Till σ=10mS/m
Shale σ=50mS/m
A
B
C
8m
5m
1m
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
EXAM 1 (25-4-1430 H)
1) What is the required frequency that can be used for detecting a conductor body
locating at 30m depth? The conductivity of the overburden layer that overlies
the conductor body is 0.01 mho/m. the available frequency that can be used is
106 , 104 and 103 Hz.
2) Draw the vector diagram in the case of presence good conductor, intermediate
and poor conductor medium.
3) Derive the equation that calculates the apparent conductivity in terms of the
cumulative relative function.
4) Calculate the EM31 apparent conductivities that would be measured above the
following geological section:
20 ft
10 ft
30 ft
σ = 4 mmhos/m
σ=100 mmhos/m
σ = 4 mmhos/m
σ = 10 mmhos/m
KING ABULAZIZ UNIVESITY
FACULTY OF EARTH SCIENCES
DEPT. OF GEOPHYSICS
ELECTROMAGNETIC METHOD
EGP431 LABORATORY SECTION
LAB. NO. 10
1) Calculate the travel time for a radar wave and a seismic air wave to reflect
from an object half a meter a way. The velocity of the seismic air wave is 300
m/s.
2) Calculate the wavelength of the radar waves and compression seismic waves
in granite.
Radar waves
Compression seismic
waves
Velocity (m/s)
1.3 x 108
5000
Frequency (Hz)
200000000
100
3) Calculate the radar wave velocity through dry sand and compare this to
seismic P-wave velocity for dry sand.
The dielectric permittivity (ε)bof dry sand = 3-10
P- wave velocity through dry sand = 200 – 1000 m/s
4) Calculate the smallest layer that can be resolved using 1 GHz antenna versus a
100 MHz GPR antenna, assuming the radar velocity in the subsurface media is
V = 0.8 x108 m/s
5) Using the following figure, calculate the velocities of the air wave, ground
wave, and reflected waves of the CMP measurements, show your work.