Dimensionless pressure drop across a skin at the well face


\(k\): Effective Permeability of Flowing Phase (D)

\(h\): Net Formation Thickness (m)

\(P_{i}\): Initial Reservoir Pressure (psi)

\(P_{1 h r}\): Pressure at 1 hour on semi-log straight line or its extension (psi)

\(P_{w s}\): Shut in Pressure (psi)

\(P_{w f}\): Bottomhole Pressure at a flowing well (psi)

\(v_{s c}\): Specific Volume at Standard Conditions \((\mathrm{cc} / \mathrm{g})\)

\(q\): Production Rate \(\left(\mathrm{m}^{3} / \mathrm{h}\right)\)

B: Formation Volume Factor (Reservoir Volume/Standard Volume)

\(\mu\): Viscosity of Flowing Fluid (cP)

\(c_{t}\): Total System Effective Isothermal Compressibility \(\left(\mathrm{kg} / \mathrm{cm}^{2}\right)^{-1}\)

\(r_{w}\): Well Radius \((\mathrm{m})\)

\(m\): Slope of Semi-Log Graph \(\left(\mathrm{kg} / \mathrm{cm}^{2}\right) / \log\) cycle for Liquid

\(\varnothing\): Porosity (Per cent)


\(P_{D w}\): Dimensionless Pressure at the well face (dimensionless)

\(s\): Skin Effect (dimensionless)


\[ \begin{gathered} P_{D w}+s=\frac{k h\left(P_{i}-P_{w s}\right)}{0.4568 v_{s c} q B \mu} \\ s=1.151\left[\frac{\left(P_{1 h r}{ }^{2}-P_{w f}{ }^{2}\right)}{m}-\log _{10} \frac{k}{\varnothing \mu c_{t} r_{w}^{2}}+0.0919\right] \end{gathered} \]


Ramey Jr, H. J. (1981). Reservoir Engineering Assessment of Geothermal Systems. Department of Petroleum Engineering, Stanford University, Page: (5.13).

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