# Permeability and skin factor from a constant-rate flow test

## Input(s)

$$t_{a}$$: Time at Pwf1 from given values or trendline (h)

$$t_{b}$$: Time at Pwf 2 from given values or trendline (h)

$$p_{w}$$: Well flowing Pressure at point 2 from given values or trend line (psi)

$$p_{w f}$$: Well flowing Pressure at point 1 from given values or trendline (psi)

$$p_{i}$$: Initial Pressure (psi)

$$\mathrm{p}_{\mathrm{hr}}$$: Pressure Value at $$t=1 \mathrm{~h}(\mathrm{psi})$$

q: Flow Rate (STB/day)

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

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

$$\mu$$: Viscosity of Oil (cP)

$$\varnothing$$: Porosity (fraction)

$$c_{t}$$: Compressibility (1/psi)

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

## Output(s)

s: Skin Factor (dimensionless)

## Formula(s)

$s=1.151 *\left(\frac{p_{i}-p h r}{\frac{p_{w f}-p_{w}}{\log \left(t_{b}\right)-\log \left(t_{a}\right)}}-\log \left(\frac{162.6 * q * B * \frac{\mu}{\left(\frac{p_{w f}-p_{w}}{\log \left(t_{b}\right)-\log \left(t_{a}\right)}\right) * h}}{\varnothing * \mu * c_{t} * r_{w}^{2}}\right)+3.23\right)$

## Reference(s)

Pressure Buildup and Flow Tests in Wells, Matthews & Russell, Page: 57.

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