In the wellbore storage regime, the derivative slope is constant at what value?

In the wellbore storage regime, the derivative slope is constant at what value?

• A. Zero
• B. Two
• C. One
• D. Five

Answer: (C)

In the early, wellbore storage–dominated period, the pressure response is governed by the fluid that’s trapped in the wellbore itself, not by flow into the formation. This causes the pressure change to vary with the logarithm of time, so when you plot the dimensionless pressure against the logarithm of time, you get a straight line. In the standard normalized form used for PetroBowl-style analysis, that line has a constant slope of one. So the derivative with respect to the logarithm of time is constant and equal to 1.

In the early, wellbore storage–dominated period, the pressure response is governed by the fluid that’s trapped in the wellbore itself, not by flow into the formation. This causes the pressure change to vary with the logarithm of time, so when you plot the dimensionless pressure against the logarithm of time, you get a straight line. In the standard normalized form used for PetroBowl-style analysis, that line has a constant slope of one. So the derivative with respect to the logarithm of time is constant and equal to 1.