Prats effective well radius

Prats effective well radius equation

Prats effective well radius

Effective well radius is a radius value at which well is draining the reservoir under the radial flow conditions.

• For stimulated wells the effective well radius is higher than the wellbore radius.
• For damaged wells the effective well radius is lower than the wellbore radius.
• For undamaged wells the effective well radius is equal to the wellbore radius.

$r_{w_{eff}}=r_w e^{-S}$

It appears that the behavior of vertically fractured reservoirs can be interpreted in terms of simple radial-flow reservoirs of large wellbore.

— Prats, 1961

Skin equation for fractured wells

For high conductivity fracture:

$r_{w_{eff}} = \frac{X_f}{2}$

and

$S = ln \left ( \frac{r_w}{r_{w_{eff}}} \right ) = ln \left ( \frac{2 r_w}{X_f} \right )$

Nomenclature

$r_{w}$ = wellbore radius, length

$r_{w_{eff}}$ = effective well radius, length

$S$ = skin factor, dimensionless

$X_f$ = fracture half length, length

References

1. Prats, M., Hazebroek, P., and Strickler, W.R. 1962. Effect of Vertical Fractures on Reservoir Behavior--Compressible-Fluid Case. SPE J. 2 (2): 87-94.