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Normalised dimensionless difference between the sandface bottomhole pressure (BHP)
and the
sandface r
eservoir pressure LaTeX Math Inline |
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body | \displaystyle p({\bf r}, t) |_{{\bf r} \in \Gamma_s} |
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at the boundary
of
damaged reservoir zone :
LaTeX Math Block |
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anchor | SMSMdef |
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alignment | left |
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S_M = \frac{2 \pi \sigma}{q_t} \cdot \left[ p_{wf}(t) - p({\bf r}, t) |_{{\bf r} \in \Gamma_s} \right] |
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The
LaTeX Math Block Reference |
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can be re-wrriten as: LaTeX Math Block |
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anchor | P_wf_skin |
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alignment | left |
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p_{wf}(t) = p^o_{wf}(t)| - \frac{q_t}{2 \pi \sigma} \ S_M |
with the meaning that near-reservoir damage is resulting in additional pressure drop quantified by the value of mechanical skin-factor
It quantitatively characterises permeability change in a thin layer (usually < 1 m) around the well or around the fracture plane, caused by stimulation or deterioration during the reservoir invasion under drilling or well intervention or under routine production or injection.
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The most popular practical range of skin-factor variation is
with upper limit
going arbitrarily highmay sometimes extend further up.For the negative skin-factor values there is a natural limitation from below caused by the Mechanical Skin concept itself.
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LaTeX Math Block |
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k_s = k \cdot \left[ 1+\frac{S_M}{ \ln \frac{r_s}{r_w}} \right]^{-1} \rightarrow \infty \, \mbox{ when } S_M \rightarrow -5 |
In other words, the highly negative skin-factor
should be modelled as composite area around near-reservoir zones rather than using the concept of Mechanical Skin.
For horizontal wells the lower practical limit when Mechanical Skin concept can be applied is even lower and usually assumed as 0.
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