# Radius of investigation (shut-in time)

## Input(s)

\(\mathrm{dt}\): Time of shut in (h)

\(\mathrm{k}\): Permeability \((\mathrm{mD})\)

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

\(\varnothing\): Porosity (fraction)

\(c_{t}\): Compressibility \((1 / \mathrm{psi})\)

## Output(s)

\(r_{i}\): Radius of investigation \((\mathrm{ft})\)

## Formula(s)

\[
r_{i}=\left(k^{*} \frac{d t}{948 * \varnothing * \mu * c_{t}}\right)^{0.5}
\]

## Reference(s)

Pressure Buildup and Flow Tests in Wells, Matthews & Russell, Page: 117.