Question

Which of the following approaches is/are used to get the response of a Formation Micro Scanner (FMS) log?

• A. Optical
• B. Electrical
• C. Thermal
• D. Nuclear

Hint:

FMS is a microresistivity imaging tool that uses button electrodes pressed against the borehole wall.

Answer 1

The Correct Option is B

Step 1: Recall what an FMS tool is designed to do: 
The Formation MicroScanner is a wireline logging tool that produces a high resolution, oriented image of the borehole wall. It is primarily used to identify thin bedding, fractures, vugs, sedimentary structures and dip of formation layers from a detailed picture of the rock surface just outside the borehole.

Step 2: Recall the physical principle the tool is built on: 
The FMS pad carries an array of small button electrodes that are pressed firmly against the borehole wall. A focused electrical current is emitted from these buttons into the formation, and the tool measures the micro resistivity of the rock immediately beneath each button as the tool is pulled up the hole. Because the resistivity of the rock varies with lithology, porosity and the presence of fractures, plotting these micro resistivity measurements from many closely spaced buttons builds up a detailed electrical image of the borehole wall.

Step 3: Rule out the other listed approaches: 
The FMS response is not based on optical imaging, since there is no camera or light based sensing involved in a standard borehole environment where visibility is essentially impossible. It is not a thermal method, since it does not rely on temperature measurement. It is also not a nuclear method, since it does not use radioactive sources or detect gamma rays or neutrons, unlike tools such as the gamma ray log or neutron porosity log.

Step 4: Conclude the correct approach: 
Since the FMS response is generated purely from micro resistivity measurements made through button electrodes in contact with the formation, the only correct approach among the choices is the electrical approach.

Final Answer: 
\[ \boxed{\text{Electrical (Option B)}} \]