jeopardy exam 2 well log data

Question 1

What does a high gamma ray value tell us? A low value?

Answer 1

High-shaley area, sandy area

Question 2

Gamma Ray logs are measured in what unit?

Answer 2

API

Question 3

What does the SP curve normally indicate (i.e. porosity, lithology, resistivity, etc.). What does it measure? (i.e the gamma ray log measures changes in natural radiation from a formation, so what does SP do?)

Answer 3

SP curve normally is an indicator of lithology. SP (spontaneous potential) gives a measure of potential difference between a point in the wellbore and an electrode on the surface. Units of millivolts (mV).

Question 4

If your ILD log is low through a given section, and your SFL log is high through the same section, what does that say about the reservoir/bore fluid through that section (think critically, what does each tool tell us about the reservoir/wellbore)?

Answer 4

There is probably an oil based mud leakage through the wellbore and into the reservoir/formation

Question 5

As the neutron porosity curve crosses below the density porosity curve, there is a large indicator of a gas zone. Explain why.

Answer 5

The neutron porosity curve gives a hydrogen index, or basically the amount of neutrons within the hydrogen in formation. The density porosity curve gives the electron density, but often this is close to the bulk density of the formation. Even though the gas is a hydrocarbon, the density is very low, so the neutron porosity curve will drop.