Pressure Buildup Test Calculator
Horner analysis of pressure buildup tests. Calculate reservoir pressure, effective permeability, and skin factor from field measurements.
Reservoir & Well Parameters
Horner Plot — MTR Slope
Enter two points from the Middle Time Region (MTR) straight line on the Horner plot [log((tp+Δt)/Δt) vs Pws].
Point 1 (MTR)
Point 2 (MTR)
Equations used (Horner analysis)
MTR Slope: m = (Pws2 - Pws1) / log(HTR1/HTR2) [psi/cycle]
Permeability: k = 162.6 × q × μ × Bo / (m × h) [md]
P* Extrapolation: Linear extrapolation of MTR line to HTR = 1
Skin Factor: S = 1.1513 × [(Pws,1hr - Pwf)/m - log(k/(φ×μ×ct×rw²)) + 3.2275]
Reference: Lee, J., Well Testing, SPE Textbook Series Vol. 1.
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A pressure buildup test is conducted by producing a well at a stabilized rate for time tp, then shutting it in and recording the pressure recovery over time. The resulting data, plotted as shut-in pressure Pws versus the Horner time ratio (tp+Δt)/Δt on a semi-log scale, forms a straight line in the middle time region (MTR). The slope m of this line is the foundation of Horner analysis.
The MTR slope directly yields effective formation permeability through the equation k = 162.6qμBo/(mh). High permeability means a steeper pressure recovery; low permeability means slower recovery and a smaller slope magnitude. The extrapolated pressure P* (where the MTR line intersects HTR=1) is an estimate of average reservoir pressure for infinite-acting reservoirs. Skin factor S, calculated from the 1-hour pressure intercept, quantifies wellbore damage (S>0) or stimulation (S<0).
This calculator requires identifying two clean points from the MTR straight-line portion of the Horner plot. Early time data is distorted by wellbore storage effects; late time data may show boundary effects. The validity window is determined by the dimensionless wellbore storage constant and the reservoir geometry. Built by Groundwork Analytics.