Question

Given below are two statements:
Statement (I): Well logging consists of recording the characteristic properties of the samples of sub surface materials obtained during the progress of test drilling.
Statement (II): Geophysical methods provide indirect evidence of the sub surface formations that indicates whether the formations may possibly be aquifers.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Electrical resistivity well logging is widely used because freshwater-bearing sand formations have high resistivity, whereas clay formations or saltwater-bearing sands have very low resistivity.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Groundwater exploration involves locating productive aquifers prior to drilling water wells.
This is accomplished using surface geophysical surveys (which provide indirect sub-surface information) and subsurface well logging (which provides direct, in-situ physical measurements within a borehole).

Step 2: Detailed Explanation:
Let us evaluate Statement (I):
Well logging involves lowering measuring probes (sondes) down a drilled borehole to record the physical, chemical, and electrical properties of the surrounding formations.
It also includes geologic logging, which analyzes physical drill cuttings brought to the surface during drilling.
This provides a continuous record of the subsurface geological profile.
Thus, Statement (I) is correct.
Let us evaluate Statement (II):
Surface geophysical methods (such as electrical resistivity, seismic refraction, and electromagnetic methods) measure physical fields at the surface.
These measurements are interpreted to estimate subsurface properties like electrical resistivity and seismic velocity.
While these methods do not detect water directly, they help identify water-bearing geological structures (such as fractured rock zones or sand-gravel layers) that could act as aquifers.
Thus, Statement (II) is correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are correct.