Question

Two sandstone reservoir rocks R1 and R2 have 25 % porosity each but the permeability of R1 is higher than that of R2. Which of the following can explain this difference in permeability?

• A. Clay content in R1 is more than that in R2
• B. Microfracture density in R1 is higher than that in R2
• C. Sorting in R1 is better than that in R2
• D. R1 has more angular grains than R2

Hint:

In sedimentary rocks, better sorting leads to higher permeability as it creates more uniform pore spaces that allow fluids to flow more easily.

Answer 1

The Correct Option is C

Step 1: Porosity versus permeability.
Both rocks hold the same 25 percent pore space, yet R1 lets fluid through more easily. So we need what makes the pores better connected, not just bigger in total.

Step 2: The role of sorting.
When grains are well sorted, all of one size, the pores between them stay open and link up well. That raises permeability even at the same porosity.

Step 3: Apply it to R1.
If R1 is better sorted than R2, its pore throats are wider and cleaner, so fluid moves faster. This explains the higher permeability.

Step 4: Reject the others.
More clay would clog pores and lower flow. Angular grains lock tight and shrink throats. Microfractures are not stated for either rock. So those do not explain it.

Step 5: Final choice.
The reason is that R1 is better sorted than R2.
\[ \boxed{\text{Sorting in R1 is better than that in R2}} \]