# Dimensionless pressure drop across a skin at the well face

## Input(s)

\(k\): 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)

## Output(s)

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

\(s\): Skin Effect (dimensionless)

## Formula(s)

## Reference(s)

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