Normalised dimensionless difference between the actual drawdown wellbore pressure p_{wf}(t) and a model of a full-entry vertical well with homogeneous reservoir and non-damaged near-reservoir zone p^*_{wf}(t):
S = \frac{2 \pi \sigma}{q_t} (p_{wf}(t) - p^*_{wf}(t)) |
where
q_t – total sandface rate
\sigma – formation transmissibility
By definition the skin-factor is a pressure adjustment at the well wall and does not affect pressure distribution in reservoir away from wellbore r > r_s.
The total skin is usually decomposed to
Geometrical skin S_G, related to deviation of the well-reservoir contact from the simplest model
and
Mechanical skin S_M, related to pressure drop caused by the near-reservoir zone formation damage:
S_T = S_G + S_M |