Electrical%20Resistivity

1
Electrical Resistivity

• R A/L ?V/I
• R resistivity
• A cross-sectional area of current flow
• L length of the flow path
• ?V voltage drop
• I electrical current

2
Resistivity

• Dry materials
• Gravel
• Salt water

• Wet materials
• Silt or clay
• Fresh water

3
R 2?a ?V/I
Wenner array
a
a
a
Schlumberger array
R ?(AB/2)2-(MN/2)2/MN ?V/I
Dipole-dipole array
R n(n1)(n2)a ?V/I
4
Resistivity Surveys

• Electrical sounding variations of apparent
  resistivity with depth.
• Horizontal profiling lateral variations in
  resistivity.

5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
Higher level Of dissolved solids
9
(No Transcript)
10
Methods

• Seismic
• Gravity
• Aeromagnetic
• Magnetometer

• Seismic velocities
• Density variation
• Magnetic fields
• Magnetic fields

11
Seismic Methods

• Seismic velocities.

12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Magnetometer Surveys and GPR

• Magnetic field especially useful for metal
  detection.
• Ground-penetrating radar electromagnetic field.

16
Gravity and Aeromagnetic Methods

• Aeromagnetic surveys measure magnetic anomalies
  which would be distorted by magnetic materials in
  the crust useful in indicating the depth to
  magnetic basement rocks.
• Gravity surveys measure gravity anomalies
  reflections of mass distribution in the crust.

17
(No Transcript)
18
(No Transcript)
19
Geophysical Logs

• Caliper measure the diameter of an uncased
  borehole in bedrock units.
• Temperature temperature of the fluid.
• Resistance
• Resistivity
• Spontaneous potential natural electrical
  potential that develops between the formation and
  the borehole fluids determination of bed
  thickness, geologic correlation, delineation of
  permeable rocks.

20
(No Transcript)
21
Sandstone, clay
22
(No Transcript)
23
Nuclear Loggings

• Natural Gamma Radiation emission of gamma
  activity by K40, U238, Th232
• Neutron logging measure gamma radiation
  produced by neutron-hydrogen atom collision -
  Hydrogen is related to water content soil
  moisture or porosity below water table.
• Gamma-Gamma radiation gamma radiation produced
  by a source, such as cobalt 60, is absorbed or
  scattered by the materials in contact with the
  source. The adsorption is proportional to the
  bulk density of the earth material.

24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
Near borehole (with fluid influence)
Average
Lower resolution
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)