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Normalized dimensionless difference between the sandface bottomhole pressure (BHP)
and a
reservoir pressure of a reference model of a full-entry vertical well with homogeneous and non-damaged
near-well reservoir zone estimated at
wellbore radius :
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S = \frac{p_{wf}(t) - p_{\rm ref}(t, r_w)}{ \left[ r \cdot \frac{\partial p_{\rm ref}}{\partial r} \right]_{r=r_w} } |
where
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It can be interpreted as the dimensionless ratio of linear-average pressure gradient between wellbore axis () and wellbore radius to the actual pressure gradient at wellbore radius:
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S = \frac{ \frac{p_{wf}(t) - p_{\rm ref}(t, r_w)}{ r_w } }{\left[ \frac{\partial p_{\rm ref}}{\partial r} \right]_{r=r_w}} |
By definition the skin-factor is a pressure adjustment at the well-reservoir contact and does not affect pressure distribution in reservoir away from wellbore
.
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