Term
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Definition
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Term
| In high porosity rocks, the count rate will be.... |
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Definition
| The count rate will be low, since neutron will be slowed down and absorbed very quickly in short distances in formation with a large amount of hydrogen atoms. |
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Term
What are the neutron sources used in logging:
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Definition
It is a mixture of two elements (i) a source of alpha radiation such as radium, plutonium or americium, and (ii) beryllium-9
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Term
| Why does hydrogen slow down neutron most efficient? |
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Definition
The neutron has approximately the same mass as hydrogen nuclei (the lightest element). Hence the neutrons lose energy by elastic scattering most efficiently by interaction with hydrogen nuclei, and lose energy much less efficiently by interaction with more massive nuclei such as silicon or oxygen
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Term
In what energy range do we find thermal neutrons:
A) >100 keV
B) 100 keV - 100 eV
C) 100 eV - 0,01 eV
D) <0,01 eV |
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Definition
Thermal neutrons has a low energy range from 0,01 ev and less.
A) >100 keV (Fast neutrons)
B) 100 keV - 100 eV (Intermediate neutrons)
C) 100 eV - 0,01 eV (Epithermal neutrons)
D) <0,01 eV (Thermal neutrons) |
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Term
| Do thermal neutrons have a higher frequency of collisions than fast neutron? |
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Definition
No, they have fewer!
When the neutrons attain thermal energies, collisions occur much less frequently because the neutrons are moving from nucleus to nucleus much more slowly.
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Term
| What is neutron absorption? |
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Definition
Neutron absorption is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus:
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Term
What does neutron logging tool measure?
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Definition
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Most tools measure thermal neutron intensity. Tools designed for liquid filled borehole.
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Some tools measure
epithermal neutrons.
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Some tools correct for tool
acceleration and environment.
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Term
| Definition of Hydrogen Index: |
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Definition
The number of hydrogen atoms per unit volume divided by the number of hydrogen atoms per unit volume of pure water at surface conditions.
The hydrogen index (HI) is thus the density of hydrogen relative to that of water. |
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Term
| What is the hydrogen index of pure water? |
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Definition
| The hydrogen index of pure water is 1 |
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Term
| What has the highest hydrogen index of calcite and quartz? |
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Definition
| Both has a hydrogen index of 0. None of them has hydrogen atoms in their molecules. |
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Term
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Definition
| The hydrogen index will be directly proportional to the amount of water in the formation. Hence HI = φ (0,33) for completely water saturated limestones. |
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Term
What are the only two elements that are found in reservoirs that contribute significantly to neutron absorption ?
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Definition
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Term
What will happen if the drilling mud, mud filtrate or formation fluids contain a significant amount of dissolved chloride ions?
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Definition
The tool will measure a lower flux of neutrons and hence overestimate the porosity
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Term
| What is the so-called shale effect in neutron logging? |
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Definition
Shale contain clays that have a significant amount of surface absorbed (bound) water. Hence shales can contain a significant proportion of hydrogens despite being low porosity.
The apparent porosity read from the neutron tool in shale formations is therefore always significantly higher than it really is
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Term
| What will happen to the apparent neutron porosity in gas bearing interval? |
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Definition
| The neutron porosity will be underestimated due to the low gas density. |
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Term
| Why is neutron tools calibrated in pure limestone saturated with fresh water? |
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Definition
Pure limestone saturated with fresh water is chosen because it contains no elements which contribute significantly to the measured signal other than hydrogen
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Term
| Does the neutron log measure effective or total porosity? |
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Definition
| The neutron log measure total porosity |
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Term
| What is a negative separation and what is a positive separation when compared with the density log? |
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Definition
A negative separation is when the neutron log is to the right/lower side of the density log.
A positive serpation is when the neutron log is to the left/higher side of the density log. |
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