On a log-log plot of flow rate vs time, what characteristic describes storage?

• A. A Plateau in the Pressure Derivative
• B. A Hump in the Pressure Derivative
• C. A Constant Pressure
• D. A Sudden Spike in Flow Rate

Answer: (B)

Storage effects come from the wellbore and near-well region acting like a small storage volume that must be depleted or filled as production begins. On a log-log plot, this near-wellbore storage alters the early-time pressure response before the reservoir-diffusion behavior fully takes over. As stored fluid is released into the well, the pressure drop evolves more rapidly at first and then slows, which shows up as a rise to a peak in the pressure derivative and then a decay. That distinct peak is the hump, signaling that storage is influencing the response.

The other possibilities don’t fit this early-time signature. A plateau in the pressure derivative would suggest a steady rate of change over that time span, not the transient release of stored fluid. A constant pressure or a sudden spike in flow rate does not describe how the derivative evolves with time in a transient well test.