Pressure buildup equation (Horner equation)

Input(s)

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

$Q_{o}$: Stabilized Well Flow Rate before Shut-in (bbl/d)

$\mu_{o}$: Oil Viscosity $(\mathrm{cP})$

$B_{o}$: Oil Formation Volume Factor (rb/stb)

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

$\mathrm{h}$: Height (ft)

$t_{p}$: Flowing Time before Shut-in (day)

$\Delta t$: Shut-in Time (day)

Output(s)

$P_{w s}$: Pressure (psi)

Formula(s)

$$ P_{w s}=P_{i}-\left(\frac{162.6 * Q_{o} * B_{o} * \mu_{o}}{k * h}\right) * \log \left(\frac{t_{p}+\Delta t}{\Delta t}\right) $$

Reference(s)

Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 1, Page: 54 .