Free Online Well Test Analysis Tool: Permeability and Skin from Drawdown

Geology
All tools
Report
Load the demo or paste flowing pressure data from a constant-rate drawdown test. Analysis runs entirely in your browser.
The chart is the classic semilog plot: flowing pressure against the logarithm of time. Early points curve under wellbore storage; once radial flow develops the data falls on a straight line whose slope gives permeability and whose position at one hour gives skin. Set the fit start time after the storage hump; the teal line shows exactly what was fitted.

Well test analysis in your browser

Paste flowing pressure data from a constant-rate drawdown test and the tool above performs the classic semilog analysis: it plots pressure against the logarithm of time, fits the radial flow straight line beyond your chosen start time, and converts the slope and the one-hour intercept into the two numbers every well test exists to find, permeability and skin. The demo loads a synthetic 50 md test with skin of 2 and realistic wellbore storage, and the analysis recovers both, which you can verify by hand from the printed report.

Semilog well test plot of flowing pressure versus log time showing early wellbore storage curvature and the radial flow straight line whose slope gives permeability and skin
The semilog plot: after wellbore storage dies out, pressure declines one straight line per log cycle, and that slope is kh.

This is the second tool in the Reservoir Engineering Suite. Test data is commercially sensitive, and like everything on this site it never leaves your browser.

The two numbers and what they mean

Permeability comes from the slope: each tenfold increase in time drops pressure by a fixed amount, and that amount is inversely proportional to the flow capacity kh. Skin comes from where the line sits: a damaged well flows the same slope but at lower pressure, and the offset at one hour, compared against what an ideal well of that permeability would show, quantifies the damage as a dimensionless skin factor. The tool also converts skin into the pressure being wasted across the damaged zone, which is the number that justifies or kills a stimulation job: a well losing 100 psi to skin is a candidate, a well losing 5 psi is not.

Using the fit start time honestly

  • Early data bends under wellbore storage: the wellbore itself supplying fluid while the reservoir wakes up. Points before your fit start show gray and are excluded.
  • Slide the start time later and watch k and skin stabilize: when they stop moving, you are on the true radial flow line.
  • A slope that keeps steepening at late time suggests a boundary; analysis of that belongs to type-curve methods beyond this tool.
  • Buildup tests can be analyzed here too by plotting shut-in pressure against Horner time externally, but the native analysis is a constant-rate drawdown.

What this tool is for

First-pass permeability and skin from a test someone handed you, teaching semilog analysis with data students can check against the formulas, and screening which wells deserve full pressure-transient interpretation. Commercial packages add derivative diagnostics, type curves, and boundary models; the straight line fitted here is still the backbone inside every one of them.

Related Calculators and Reference