Measuring the flow rate and pressure drawdown in a producing well while the reservoir is in steady state provides what information?

• A. Porosity
• B. Permeability or skin
• C. Reservoir pressure
• D. Gas Saturation

Answer: (B)

Measuring the flow rate and pressure drawdown around a producing well in steady state reveals how readily fluids move through the rock and any extra resistance near the wellbore. In steady, radial flow, the rate at which fluid enters the well depends on the formation’s ability to transmit fluids (permeability), the thickness of the reservoir, the fluid’s viscosity, and a near-wellbore skin factor that represents damage or stimulation effects. Using the observed flow rate and pressure difference between the reservoir and the well, you can solve for the effective permeability and the skin factor (often written into the radial-flow equation as a logarithmic term plus the skin). This is why the information obtained is permeability or skin.

Porosity is about how much fluid the rock can store and is not directly determined from a steady-state drawdown test. Reservoir pressure generally comes from transient pressure data such as buildup tests or shut-in measurements, not from a simple steady-state drawdown. Gas saturation requires additional phase behavior and data beyond this steady-state flow measurement.