Question

Low value in SP log as observed in dispersed shales is mainly due to the impeded movement of:

• A. Na$^+$ ion
• B. Cl$^-$ ion
• C. K$^+$ ion
• D. OH$^-$ ion

Hint:

In SP logging, low readings in dispersed shales are often due to impeded ion movement, especially Cl$^-$.

Answer 1

The Correct Option is B

In SP (Spontaneous Potential) logging, the readings are influenced by the movement of ions in the pore water. In the case of dispersed shales, the low SP values are due to the difficulty in the movement of Cl$^-$ ions. This is because dispersed shales, which have fine particles and high clay content, tend to trap or impede the movement of chloride ions, leading to lower SP values.
[6pt] - Na$^+$ ions (A) do play a role in SP measurements, but they are not the primary cause of low values in dispersed shales.
- K$^+$ ions (C) also contribute to the overall ion movement but are less significant than Cl$^-$ ions in controlling SP readings.
- OH$^-$ ions (D) are unlikely to significantly influence the SP log in this context.
Therefore, the correct answer is (B): Cl$^-$ ions.