During infinite acting radial flow, what is the value of the pressure derivative slope?

• A. Zero
• B. One
• C. Two
• D. Three

Answer: (A)

In infinite acting radial flow, the pressure response grows logarithmically with time. When you look at how the pressure derivative with respect to log(time) behaves, that derivative is constant in this regime. Because it doesn’t change with log time, the slope of that pressure-derivative curve is zero. So the pressure derivative slope is zero.

The other numbers would imply the derivative changes with log time, which doesn’t happen in the infinite acting radial-flow case.