Quantifying formation damage and improvement

Input(s)

$p_{w f}$: Pressure of Wellflow (psi)

p: Pressure of Reservoir (psi)

s: Skin Factor (dimensionless)

$r_{s}$: Radius of skin (ft)

$r_{w}$: Radius of Wellbore (ft)

q: Flow Rate (STB/day)

$\mathrm{k}$ : Permeability of Formation (mD)

$\mu$ : Viscosity of Oil $(\mathrm{cP})$

B: Volume factor $(\mathrm{RB} / \mathrm{STB})$

$\mathrm{h}$ : Thickness of reservoir $(\mathrm{ft})$

Output(s)

$k_{s}$: Permeability of altered zone $(\mathrm{mD})$

$r_{w a}$: Effective Radius of Wellbore (ft)

E: Flow Efficiency (fraction)

Formula(s)

$$ \begin{gathered} k_{s}=\frac{k}{1+\frac{s}{\ln \left(\frac{r_{s}}{r_{w}}\right)}} \\ r_{w a}=r_{w} * 2.71828^{-s} \\ E=\frac{p-p_{w f}-\left(141.2 * q * B * \mu * \frac{s}{k * h}\right)}{p-p_{w f}} \end{gathered} $$

Reference(s)

Pressure Transient Testing, Lee, Rollins \& Spivey, Page: 43.