A formal number characterizing the size of a drainage area A_e:
(1) | r_e = \sqrt{\frac{A_e}{\pi}} |
In case of circular drainage area the drainage radius r_e takes a physical sense of a distance from well to the drainage area boundary.
See also
Physics / Fluid Dynamics / Percolation
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Field Study & Modelling / Drainage (fluid flow)