Horner Plot DST Permeability Calculator

Well testing & transient pressure analysis: Compute formation permeability (k), skin factor (s), initial reservoir pressure (P*), and radius of investigation from Horner buildup test slopes.

Test Flow & Horner Slope Data

Flow Rate Prior to Shut-in q (STB/d): Stabilized production rate

Semilog Slope m (psi/cycle): Slope of middle time region (MTR)

Net Pay Thickness h (ft): Formation net thickness

Viscosity μ (cP) & Formation Factor B:

μ (cP) / B (bbl/STB)

Pressure at 1 Hour Shut-in P_1hr (psi): Extrapolated MTR at Δt = 1 hr

Flowing Pressure at Shut-in P_wf (psi): Pressure right before shut-in (Δt = 0)

Porosity Φ (%) & Well Radius r_w (ft):

Φ (%) / r_w (ft)

Total Compressibility c_t (10⁻⁶ psi⁻¹): System rock + fluid compressibility

Transient Test Results

Formation Permeability (k)

Skin Factor (s)

Apparent Wellbore Radius (r_wa)

r_w · e^(-s)

Flow Efficiency (FE)

Ideal vs actual ratio

Pressure Drawdown (ΔP_total)

P_1hr - P_wf

Radius of Investigation (at 24h)

Transient drainage boundary

Recommended Tools & Equipment

Tested hardware and components for high reliability

100% Free Tool Zero Sign-Up

Frequently Asked Questions

What is Horner time (tp + Δt) / Δt?

Horner time is a dimensionless superposition time ratio that accounts for the prior production duration tp before the well was shut in for pressure buildup during time Δt. As shut-in time Δt approaches infinity, Horner time approaches 1.0 (log10(1) = 0), allowing extrapolation to the initial reservoir pressure P*.

Why must P_1hr be read from the straight line and not raw gauge data?

At Δt = 1 hr, early shut-in pressure is frequently distorted by wellbore storage (afterflow) and skin effects. The value of P_1hr must be extrapolated backwards or forwards along the Middle Time Region (MTR) semilog straight line to isolate genuine reservoir radial flow.

What does a slope change (dual slope) on a Horner plot signify?

A doubling of the semilog slope (from m to 2m) indicates the pressure transient has encountered a sealing no-flow fault boundary. A decrease in slope signifies a constant pressure boundary, such as a strong water drive aquifer or gas cap.