Reservoir Flow (Darcy Radial)

This equation estimates the steady oil production rate into a well when fluid moves horizontally through a cylindrical reservoir toward the wellbore. It comes from Darcy’s law applied in radial coordinates, so the flow area shrinks as the fluid gets closer to the well, which is why the logarithmic term ln(re/rw) appears. The rate increases when the pressure drop between the outer reservoir and the well is larger, and it decreases when the oil is more viscous, the formation is less permeable, or the drainage distance is effectively larger.

Use this for radial, steady-state single-phase oil flow toward a producing well, especially in reservoir engineering calculations for near-well productivity. It is commonly used to estimate well deliverability or compare how changes in permeability, viscosity, or pressure drawdown affect production.

• Using pressure increase instead of drawdown, so the sign of (Pe - Pw) is reversed
• Forgetting that the logarithm uses the radius ratio re/rw, not the difference re - rw
• Mixing units from SI and field units without changing the 141.2 constant accordingly