Geoelectrics

Question 1 of 58

1

Is the amount of pore space the most important factor controlling electrical conductivity?

Select one of the following:

True
False

Explanation

Question 2 of 58

1

What are the types of current flow?

Select one of the following:

Electronic, Ionic
Metallic, Aqueous

Explanation

Question 3 of 58

1

What are the two mechanisms by which we recognise the presence of an electrical inhomogeneity in the
Earth?

Select one or more of the following:

By the generation of current circulating within a conductive body
By the generation of current not circulating within a resistive body
By generating currents that penetrate the boundary between two regions with diferent electrical properties.
By generating currents that not penetrate the boundary between two regions with different electrical properties

Explanation

Question 4 of 58

1

The penetration of an electromagnetic field into the earth depends on:

Select one or more of the following:

Frequency of oscillation
Conductivity of the earth
Depth of investigation
Current flow paths

Explanation

Question 5 of 58

1

What is an inductive response

Select one of the following:

An inductive response occurs when current flows within the conductive region in proportion to its conductivity and the time rate of change of the applied magnetic field
An inductive response occurs when the currents will be distorted by the presence of the anomalously conductive body.

Explanation

Question 6 of 58

1

Specific exploration problems are characterised by specic ranges in depth of interest leading to diferent preferred frequencies. What are the range of depths and frequencies used in Oil and Gas exploration?

Select one of the following:

Frequency range: 1-10^-4 Hz
Depths 10-1000 m
Frequency range: 100-10^-1 Hz
Depths 10-100 m
Frequency range: 10-10^-3 Hz
Depths 1-100 m

Explanation

Question 7 of 58

1

How is called a measure of how easy it is to produce an electrical polarisation within a material?

Select one of the following:

Galvanic Response
Inductive Response
Dielectric Constant
Permitivity of the material

Explanation

Question 8 of 58

1

The electrical properties of the rocks depend on...

Select one or more of the following:

The constituent minerals
Their mineral associations
Rock porosity
Fluid content
Permitivity
Dielectric constant

Explanation

Question 9 of 58

1

The main difference between resistivity-resistance and conductivity-conductance is that the former is related to the material and is a physical property of it (intensive property: does not depend on the system size or the amount of material in the system)

Select one of the following:

True
False

Explanation

Question 10 of 58

1

The materials can be classified according to their conductivity into groups. Select the groups:

Select one or more of the following:

Conductors, conductivity less than 10^5 S/m
Semi-conductors 10^-8 S/m < Conductivity < 10^5 S/m
Insulators Conductivity < 10^-8 S/m
Metallic conductivity less than 10^5 S/m
Sulphides 10^-8 S/m < Conductivity < 10^5 S/m
Aislators Conductivity < 10^-8 S/m

Explanation

Question 11 of 58

1

Mostly, the conduction nature in rocks is mainly electronic (Metallic conduction and/or Electronic semi-conductors)

Select one of the following:

True
False

Explanation

Question 12 of 58

1

The main difference between Metallic Conduction and Electronic Semiconductors is that the latter needs a much more significant amount of energy (heat) for the electrons to become dissociated from their home atoms

Select one of the following:

True
False

Explanation

Question 13 of 58

1

In terms of Metallic conduction, it can be said that the conductivity in metals depends on:

Select one of the following:

the number density of free electrons, the electron charge and the electron mass.
the number density of free electrons, the electron charge, the electron mass and the relaxation time

Explanation

Question 14 of 58

1

Fluid conductivity depends also upon temperature because the mobility of the ions in solution decreases with temperature.

Select one of the following:

True
False

Explanation

Question 15 of 58

1

Metallic conductors resistivity depends on temperature. When the temperature increases the conductivity of the metal decreases.

Select one of the following:

True
False

Explanation

Question 16 of 58

1

When an external electric field is applied the electrons accelerate along the field lines and a current is produced. This
current would increase without limit if the electrons did not occasionally "collide" with the nuclei. The average
time between collisions for a given electron is called

Select one of the following:

The relaxation time
Intrinsic time
Extrinsic time

Explanation

Question 17 of 58

1

The electronic semi-conductors are metallic materials just as native metals, the only difference is that they have a smaller number of free electrons with lower mobility.

Select one of the following:

True
False

Explanation

Question 18 of 58

1

Electronic semi-conductors need a signicant amount of
energy for the electron to become dissociated from their "home" atoms. One source of this is heat, the number of conduction electrons in these type of material depends on:
Energy required to free an electron, Boltzmann Constant, and the absolute temperature
So it can be concluded that:

Select one of the following:

For semiconductors a higher temperature results in more free electrons and therefore a higher conductivity.
For semiconductors a higher temperature results in more free electrons and therefore a lower conductivity.
For semiconductors a higher temperature results in less free electrons and therefore a higher conductivity.
For semiconductors a higher temperature results in less free electrons and therefore a lower conductivity.

Explanation

Question 19 of 58

1

It is possible to obtain movement of ions within a solid due to imperfections

Select one of the following:

True
False

Explanation

Question 20 of 58

1

In terms of Aqueous Electrolytes, the conductivity will depend on:

Select one or more of the following:

Amount of water present
Salinity
Temperature
Connectivity
Archie's law
Cementation factor

Explanation

Question 21 of 58

1

Archie’s Law: It is a purely empirical law attempting to describe ion flow (mostly sodium and chloride) in clean, consolidated sands, with varying intergranular porosity. Electrical conduction is assumed not to be present within the rock grains or in fluids other than water.
So it can be said that the variables within the equation are:

Select one or more of the following:

An empirically defined constant
the cementation factor
Resistivity of the Aqueous solution
Porosity
Rock's bulk resistivity
Formation factor

Explanation

Question 22 of 58

1

What happens to Archie's law when part of the pore space is filled by air, natural gas, carbon dioxide or petroleum (insulators) ??

Select one of the following:

The equation remains the same
an empirical constant is added
Boltzmann constant is added to the equation
the volume fraction of pores with water power to the saturation exponent is added

Explanation

Question 23 of 58

1

The tortuosity is defined by the relation between the average length of the path through the crack and the length of the rock lc/l

Select one of the following:

True
False

Explanation

Question 24 of 58

1

The diminution ratio is the division between the cross-section area of the crack and the cross-section total area

Select one of the following:

True
False

Explanation

Question 25 of 58

1

Is a measure of the void (i.e., "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0 and 100%

Select one of the following:

Porosity
Crack
Joint

Explanation

Question 26 of 58

1

The electric permittivity is defines as...

Select one of the following:

a measure of the degree to which a given material becomes polarized.
electric dipole moment per unit volume
the amount of charge which is separated and the distance through which it has moved

Explanation

Question 27 of 58

1

The relative dielectric constant (Er or K) can be defined as...

Select one of the following:

the ratio of the material's permittivity to the permittivity of free space
the subtraction of the material's permittivity to the permittivity of free space
the multiplication of the material's permittivity to the permittivity of free space

Explanation

Question 28 of 58

1

What are the most important values in terms of relative dielectric constant

Select one of the following:

Water and Soil
Basalt, Coal Dolomite
Limestone, Granite Quartz

Explanation

Question 29 of 58

1

When the current flows more easily in some direction than in others is called Anisotropy

Select one of the following:

True
False

Explanation

Question 30 of 58

1

The longitudinal resistivity is always greater than the transverse resistivity.

Select one of the following:

True
False

Explanation

Question 31 of 58

1

The anisotropy coefficient SQRT(RT/RL) >= 1

Select one of the following:

True
False

Explanation

Question 32 of 58

1

Types of anysotropy

Select one or more of the following:

Azimuthal anisotropy (Dipping layers, Dominant set of vertical fractures)
Depth dependant anisotropy (the nature of the fracture fill changes with depth)
Transverse
Longitudinal

Explanation

Question 33 of 58

1

The main difference between IP and SP is that the former is mainly used to determine massive ore bodies whereas the latter is mainly used to determine disseminated ore bodies

Select one of the following:

True
False

Explanation

Question 34 of 58

1

Select the main uses of the SP method

Select one or more of the following:

Presence of massive ore bodies
Sulphide mineralization
Groundwater
Geothermal
Geological mapping
Chargeability

Explanation

Question 35 of 58

1

What is the cheapest and simplest method to apply? (In terms of near-surface geophysics)

Select one of the following:

SP
IP
ITS
Seismic Refraction
Gravity
GPR

Explanation

Question 36 of 58

1

The sign of the potential is an important diagnostic factor in the interpretation of SP anomalies. What kind of mineral potentials are expected for negative anomalies of hundreds of mV

Select one of the following:

Sulphide ore bodies, Graphite ore bodies, Magnetite, coal and manganese
Quartz veins, pegmatites

Explanation

Question 37 of 58

1

In mineral exploration the components of the SP are called the Mineral Potential and the "Background potential" What are the uses of the latter?

Select one or more of the following:

Massive ore bodies
Disseminated ore bodies
Geothermal research
Hydrogeological research

Explanation

Question 38 of 58

1

What type of electric conduction occurs in very weakly conducting materials (or insulators) when an external alternating
current is applied, so causing atomic electrons to be shifted slightly with respect to their nuclie.

Select one of the following:

Electrolytic
Electronic
Dielectric

Explanation

Question 39 of 58

1

How is called one of the main groups of SP that are generally of the order of mV and mainly arise due to water circulation, small
mineral quantities, biologic and topographic efects (human activities may also produce SP signals)

Select one of the following:

Electrokinetic Potential
Background Potential
Diffusion Potential
Mineral Potential

Explanation

Question 40 of 58

1

How is the called one of the main groups of SP that occur in regions of anomalous concentrations of sulfide ores (also near graphite) and
can be of the order of hundreds of mV or even V.

Select one of the following:

Electrokinetic potential
Diffusion potential
Mineral potential
Background potential

Explanation

Question 41 of 58

1

Buried sulphide masses are known to cause SP anomalies. In terms of the effect observed and the physical cause of this effect. Which of the following is true?

Select one or more of the following:

Groundwater is thought to be common factor responsible for SP. The potentials are generated by the flow of water by water acting as an electrolyte and as a solvent of different minerals.
A negative anomaly of hundreds of mV is expected
A postive anomaly of hundreds of mV is expected
One proposal can explain all SP observations
1. Above water table: dissolved electrolytes gain electrons from the ore body and are reduced.
2. Below the water table: an oxidation reaction occurs transferring electrons back to the ore body.
3. Electrons are then conducted through the ore body completing the circuit.
It is possible that only the presence of variable redox conditions within the subsurface is required to generate large SP anomalies, without need of a subsurface conductor to "close the circuit."

Explanation

Question 42 of 58

1

The SP potentials tend to increase in positiveness with the direction of water flows as the electric charge flows in the opposite direction.

Select one of the following:

True
False

Explanation

Question 43 of 58

1

How is called the mechanism by which SP anomalies are generated that is useful to map subsurface barriers or conduits of flow. (These are generated by the flow of aqueous electrolytes through narrow channels (pores))

Select one of the following:

Electrokinetic or Streaming potentials
Diffusion
Electrolytic

Explanation

Question 44 of 58

1

In practice, to ensure good ground contact in the field and to obtain reliable measurements, What sort of actions should be taken?

Select one or more of the following:

Porous-pot electrodes
Non-porous electrodes
The Resistance of the voltimeter must be large enough 10^8 Ohm
The electrodes should be kept dry and shaded to ensure good ground contact (when the fixed electrode is used)
The electrodes should be kept wet and shaded to ensure good ground contact (when the fixed electrode is used)

Explanation

Question 45 of 58

1

There are different possible arrangements in which the equipment can be deployed?

Select one or more of the following:

Static array
Fixed Spacing
Fixed Electrode

Explanation

Question 46 of 58

1

The advantage of using a fixed spacing SP survey is that you can use a shorter wire and the reduced importance of telluric currents (generally long-wavelength currents induced in the ground by geomagnetic fluctuations).

Select one of the following:

True
False

Explanation

Question 47 of 58

1

The major advantage of using a fixed spacing SP survey is that generally needs to operators to moves the system

Select one of the following:

True
False

Explanation

Question 48 of 58

1

The gridded measurements in the SP fixed spacing survey should ultimately form a closed loop and the sum of all potentials within that loop should equal zero if not the remainder represents an error and should not be distributed among the readings

Select one of the following:

True
False

Explanation

Question 49 of 58

1

The main disadvantage of using a fixed electrode system (sp) is that system include generally more measurement errors and that is not easy to perform by a single operator

Select one of the following:

True
False

Explanation

Question 50 of 58

1

The main advantage of using a fixed electrode system is that the larger separation between electrodes does not allow telluric currents to influence the results

Select one of the following:

True
False

Explanation

Question 51 of 58

1

SP can be easily executed on Ice.

Select one of the following:

True
False

Explanation

Question 52 of 58

1

Problems associated with acquiring SP data and things that must be taken into account:

Select one or more of the following:

Electrode polarization
Rain (Ground-contact strength and ground conductivity)
Telluric variations (Daily drift variations)
Artificial sources of electricity in the surroundings (or in the vicinity)
A shift in the equipotential lines in relation to an ore body (current will flow preferentially in the less resistive unit.)
Longness of the wire

Explanation

Question 53 of 58

1

the observed current and potential due to a single source in a half space is identical to that from the method of images inspired model of two sources in an infinite space.

Select one of the following:

True
False

Explanation

Question 54 of 58

1

Consider a vertical, infinite length, ellipsoidal ore body. Sketch the expected SP anomaly profile over this body

Select one or more of the following:

A vertically body will have no positive anomaly
A vertically body will have a positive anomaly
the anomaly peaks are not simply located above the poles
the anomaly peaks are simply located above the poles
For a dipping body, the negative anomaly associated with the shallower, negative pole is much more pronounced
For a dipping body, the negative anomaly associated with the shallower, negative pole is much less pronounced
A vertically body will have a negative anomaly that will be centered on the negative pole (in an homogeneous medium).
A vertically body will have a positive anomaly that will be centered on the negative pole (in an homogeneous medium).

Explanation

Question 55 of 58

1

For a tilted ore body how can you determine the depth to the sink

Select one of the following:

From the half-width of the anomaly profile x1/2=h0.73
From the half-width of the anomaly profile x1/2=h0.766

Explanation

Question 56 of 58

1

For a Vertically ore body (finite length l) how can you determine the depth to the sink

Select one of the following:

From the half-width of the anomaly profile x1/2=h0.73
From the half-width of the anomaly profile x1/2=h0.766

Explanation

Question 57 of 58

1

Is the method of the ratio and the method of the Vmin give the true position of the ore body

Select one of the following:

True
False

Explanation

Question 58 of 58

1

When the profile is drawn the
reference (zero) potential needs to be set as the value for which the potential becomes constant far from the
body, this process is helped by a good lateral extent of measurements and a low level of noise.

Select one of the following:

True
False

	Created by Vanerahal over 9 years ago

Exam1

Geoelectrics

Question 1 of 58

Is the amount of pore space the most important factor controlling electrical conductivity?

Select one of the following:

Explanation

Question 2 of 58

What are the types of current flow?

Select one of the following:

Explanation

Question 3 of 58

What are the two mechanisms by which we recognise the presence of an electrical inhomogeneity in the Earth?

Select one or more of the following:

Explanation

Question 4 of 58

The penetration of an electromagnetic field into the earth depends on:

Select one or more of the following:

Explanation

Question 5 of 58

What is an inductive response

Select one of the following:

Explanation

Question 6 of 58

Specific exploration problems are characterised by specic ranges in depth of interest leading to diferent preferred frequencies. What are the range of depths and frequencies used in Oil and Gas exploration?

Select one of the following:

Explanation

Question 7 of 58

How is called a measure of how easy it is to produce an electrical polarisation within a material?

Select one of the following:

Explanation

Question 8 of 58

The electrical properties of the rocks depend on...

Select one or more of the following:

Explanation

Question 9 of 58

The main difference between resistivity-resistance and conductivity-conductance is that the former is related to the material and is a physical property of it (intensive property: does not depend on the system size or the amount of material in the system)

Select one of the following:

Explanation

Question 10 of 58

The materials can be classified according to their conductivity into groups. Select the groups:

Select one or more of the following:

Explanation

Question 11 of 58

Mostly, the conduction nature in rocks is mainly electronic (Metallic conduction and/or Electronic semi-conductors)

Select one of the following:

Explanation

Question 12 of 58

The main difference between Metallic Conduction and Electronic Semiconductors is that the latter needs a much more significant amount of energy (heat) for the electrons to become dissociated from their home atoms

Select one of the following:

Explanation

Question 13 of 58

In terms of Metallic conduction, it can be said that the conductivity in metals depends on:

Select one of the following:

Explanation

Question 14 of 58

Fluid conductivity depends also upon temperature because the mobility of the ions in solution decreases with temperature.

Select one of the following:

Explanation

Question 15 of 58

Metallic conductors resistivity depends on temperature. When the temperature increases the conductivity of the metal decreases.

Select one of the following:

Explanation

Question 16 of 58

When an external electric field is applied the electrons accelerate along the field lines and a current is produced. This current would increase without limit if the electrons did not occasionally "collide" with the nuclei. The average time between collisions for a given electron is called

Select one of the following:

Explanation

Question 17 of 58

The electronic semi-conductors are metallic materials just as native metals, the only difference is that they have a smaller number of free electrons with lower mobility.

Select one of the following:

Explanation

Question 18 of 58

Select one of the following:

Explanation

Question 19 of 58

It is possible to obtain movement of ions within a solid due to imperfections

Select one of the following:

Explanation

Question 20 of 58

In terms of Aqueous Electrolytes, the conductivity will depend on:

Select one or more of the following:

What are the two mechanisms by which we recognise the presence of an electrical inhomogeneity in the
Earth?

When an external electric field is applied the electrons accelerate along the field lines and a current is produced. This
current would increase without limit if the electrons did not occasionally "collide" with the nuclei. The average
time between collisions for a given electron is called