Gamma Ray Logs
Assessment Gamma Ray Logs
1. From which primary isotopes in the formation does the gamma ray record radiation? (Select all that apply.)
A .Potassium-40 (K40)
B .Thorium (Th)
C .Uranium (U)
D .Cesium
2. Which of the following can have perturbing effects on gamma ray log data? (Select all that apply.)
A .Casing and cementing parameters
B .Mud weight
C .Temperature
D .Sonde position and borehole size
3. To which stable isotope do Uranium 235, Uranium 238, and Thorium 232 all decay?
A .Iron
B .Copper
C .Lead
D .Zinc
4. What are the standard units for a gamma ray log?
A .TC
B .ft/sec
C .API
D .meV
5. Potassium-40 emits gamma rays with a single radiation energy of ____________ meV.
6. Which of the following can be perturbing effects on gamma ray logs? (Select all that apply.)
A .Cement thickness in cased wellbores
B .Borehole size
C .Oil base mud
D .Sonde position in the hole
E .Mud weight
F .Casing size and weight
7. Which material decomposes at a relatively rapid rate into clay minerals, resulting in radioactive elements being trapped in the rock fabric?
A .Calcite
B .Dolomite
C .Quartz
D .Feldspar
8. On a gamma ray log, in what direction does gamma ray activity increase?
A .It depends on the service company’s convention
B .There is no standard convention
C .From left to right
D .From right to left
9. What logging speed and time constant (TC) would be considered standard for most gamma ray surveys?
A .2400 feet per hour; TC of 2 seconds
B .1800 feet per hour; TC of 5 seconds
C .1800 feet per hour; TC of 2 seconds
D .3600 feet per hour; TC of 5 seconds
10. A natural gamma ray ranges between the narrow limits of 18 and 20 API units in a clean sandstone interval within a shaly sandstone formation. In an adjacent 100% shale zone, the log varies from 91 to 95 API units. Assuming that there is a linear relationship between the gamma ray log reading and the shale content, estimate the percentage shale volumes when the gamma ray reads a) 47 and b) 73 API units.
A .28%; 70%
B .38%; 73%
C .58%; 83%
D .48%; 80%
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