Drawdown Test Analysis
Compute permeability and skin factor from constant-rate drawdown test data using semilog straight-line analysis. Browser-based drawdown analysis.
Reservoir & Well Parameters
Drawdown Pressure Data
Enter time (hr) and flowing bottomhole pressure Pwf (psi). Data is pre-filled with a synthetic drawdown example.
| # | Time (hr) | Pwf (psi) |
|---|
Semilog Straight Line Selection
Select the start and end points of the semilog straight line (middle-time region, after wellbore storage, before boundary effects).
k = 162.6 × q × B × μ / (|m| × h)
S = 1.1513 × [(Pi - P1hr) / |m| - log(k / (φ × μ × ct × rw²)) + 3.2275]
Permeability, k
--
Skin Factor, S
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Slope, |m| (psi/cycle)
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P1hr (psi)
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Semilog Plot (Pwf vs log t)
Cartesian Plot (Pwf vs t)
How this was calculated
Semilog Analysis (Horner/MDH): During infinite-acting radial flow, Pwf vs log(t) plots as a straight line with slope m. Permeability is derived from the slope, and skin from the P1hr intercept.
Assumptions: Single-phase, slightly compressible fluid. Homogeneous, isotropic reservoir. Constant rate production. Infinite-acting (no boundary effects in selected region).
Limitations: Wellbore storage effects distort early-time data. Boundary effects distort late-time data. Select only the middle-time region for the straight line.
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Book a free strategy call →Understanding Drawdown Test Analysis
A constant-rate drawdown test is one of the fundamental well testing techniques in petroleum engineering. The well is produced at a constant rate, and the flowing bottomhole pressure (Pwf) is recorded over time. By plotting Pwf versus the logarithm of time, the reservoir engineer can identify a straight-line portion corresponding to infinite-acting radial flow (IARF). The slope of this line directly yields formation permeability, and the intercept at t=1 hour gives the skin factor.
This tool implements the classical semilog analysis method described by Horner (1951) and Matthews-Brons-Hazebroek. The permeability equation k = 162.6 qBμ / (|m|h) uses oilfield units. The skin factor quantifies near-wellbore damage (positive S) or stimulation (negative S). Commercial well test software performs similar analyses with additional features like derivative analysis and deconvolution.
All calculations run in your browser. Built by Groundwork Analytics.