Which log determines the porosity of different formations?

The correct choice regarding determining the porosity of different formations is the acoustic log. An acoustic log measures the travel time of sound waves through the geological formations. The way these sound waves propagate can be influenced by the amount of fluid-filled porosity present within the rock.

In formations where higher porosity exists, sound waves tend to travel slower due to the presence of more voids filled with fluids, such as water or hydrocarbons. Conversely, in denser or more compact formations with lower porosity, sound waves travel faster. By analyzing the time it takes for the sound waves to return to the receiver, geoscientists can infer the porosity of the rock formation.

The caliper log, temperature log, and drilling log each provide valuable information about subsurface characteristics but do not directly quantify porosity like the acoustic log does. The caliper log measures the diameter of the borehole, the temperature log records temperature variations, and the drilling log contains information about the drilling process and rock cuttings but does not assess porosity directly. Therefore, the acoustic log is the most suitable tool for determining the porosity of formations.