Determine the volume of shale
Measure formation permeability
Identification of gas bearing formations
Estimation of formation true resistivity
Estimation of hydrocarbon density
Determine formation porosity
Determine lithology
Crystal is composed of sodium chloride NaCl
Scintillation crystal coupled to a photo multiplier tube
Gamma rays interact with the scintillation crystal
Electrons pass through high voltage fields to produce several secondary electrons
Electrons are ejected from the photo multiplier tube
Photoelectric factor
Tortuosity factor
Cementation exponent
Saturation exponent
Cased Hole
Freshwater-based mud
Saltwater-based mud
Air-drilled holes
Cesium-137
Americium/Beryllium
Cobalt 60
Thorium
Energy loss in gamma rays can be related to physical characteristics of the formation
Gamma rays interacting with electrons in formation gain energy
100 keV
1000 keV
10,000 keV
True
False
True
False
The electron absorbs the gamma ray and is ejected from its shell
The electron is displaced to an outer shell
The electron remains in an unchanged state
Higher energy (>100 keV) gamma rays collide with an outer shell electron and transfers some of its energy to that electron.
Higher energy (>100 keV) gamma rays collide with an inner shell electron causing the electron to move to an outer shell
Low energy (
Low energy (
100 keV
1 MeV
1000 keV
10,000 keV
Photoelectric absorbsion
Compton scattering
Scintillation
2
1
3
4
True
False
CORM curve
CORP curve
RHOB curve
CORM curve
CORP curve
RHOB curve
Positive
Negative
No change
Positive
Negative
No Change
Any physical separation between a detector and formation
Distance between source and short-spaced detector
Physical distance between the short-spaced and long-spaced detector
Distance traveled by gamma rays from the source to the point at which it is absorbed
Cased Hole
Freshwater-based mud
Saltwater-based mud
Air-drilled holes
True
False
662
62
6,662
Outer
Inner
Outer
Inner
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