For a late-time drawdown, which flow regime is indicated by the overlay of pressure change and pressure derivative?

For a late-time drawdown, which flow regime is indicated by the overlay of pressure change and pressure derivative?

• A. Pseudo steady state
• B. Steady state
• C. Transient
• D. Diffusive

Answer: (A)

Late-time drawdown is testing pseudo-steady-state flow. When the reservoir near the well has adjusted to production, the rate at which pressure at the well declines becomes nearly constant. If you overlay the pressure change (Δp) with the pressure derivative (dp/dt) over time, you’ll see Δp grow roughly linearly with time while dp/dt stays about constant. That alignment is the signature that the system has reached pseudo-steady-state radial flow: the drainage behaves as if the pressure field around the well is changing at a steady rate rather than continually accelerating or decelerating. In contrast, steady-state would imply no further time variation in pressure, which isn’t the case in drawdown; transient describes evolving flow with changing dp/dt during earlier periods; and diffusive is not the late-time, linear-behavior regime observed here.

Late-time drawdown is testing pseudo-steady-state flow. When the reservoir near the well has adjusted to production, the rate at which pressure at the well declines becomes nearly constant. If you overlay the pressure change (Δp) with the pressure derivative (dp/dt) over time, you’ll see Δp grow roughly linearly with time while dp/dt stays about constant. That alignment is the signature that the system has reached pseudo-steady-state radial flow: the drainage behaves as if the pressure field around the well is changing at a steady rate rather than continually accelerating or decelerating.

In contrast, steady-state would imply no further time variation in pressure, which isn’t the case in drawdown; transient describes evolving flow with changing dp/dt during earlier periods; and diffusive is not the late-time, linear-behavior regime observed here.