Decline Curve Forecast Calculator

Work out decline curve forecast instantly with clear inputs, formula shown and shareable results.

About Decline Curve Forecast Calculator

Arps decline curves describe rate against time with a single exponent b: exponential (b = 0) for solution-gas drive and pressure depletion, harmonic (b = 1) for gravity drainage, and hyperbolic in between, which fits most unconventional wells. Cumulative production is the integral of the rate curve.

Formulas

Exponential decline

q(t) = qi x e^(-D t); Np = (qi - q) / D

Hyperbolic decline

q(t) = qi x (1 + b D t)^(-1/b); Np = qi / (D (1-b)) x (1 - (q/qi)^(1-b))

Worked example

With the default values below, Decline Curve Forecast Calculator returns Cumulative Production of 1,180,207. Change any input above and every figure here is recalculated in your browser.

Inputs used

Initial Production Rateminimum 0 bbl/day: 800 bbl/day
Annual Decline Rateaccepts 0.01–99 %: 22 %
Decline Typeone of Exponential (b = 0), Harmonic (b = 1), Hyperbolic (b = 0.5): Exponential (b = 0)
Forecast Periodminimum 0.01 years: 10 years

Results

Cumulative Production: 1,180,207
Rate At End Of Forecast: 88.643
Decline Exponent b: 0.00
Average Rate Over Period: 323.344

Step by step

1Values used
2Exponential decline
3Hyperbolic decline
4Cumulative Production= 1,180,207
5Rate At End Of Forecast= 88.643
6Decline Exponent b= 0.00
7Average Rate Over Period= 323.344

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Reserve estimates derived from decline curve analysis must be prepared or audited by a qualified reserves evaluator for any financial or regulatory reporting.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Reserve estimates derived from decline curve analysis must be prepared or audited by a qualified reserves evaluator for any financial or regulatory reporting.

Frequently Asked Questions

Which b value should be used?

Fit it to at least 12-18 months of production history. Shale wells commonly show b between 0.8 and 1.4 early on, transitioning to exponential later, so a terminal decline rate must be imposed.

Why cap harmonic decline?

Harmonic and high-b hyperbolic curves predict infinite cumulative production. A terminal exponential decline, typically 5-8% a year, must be applied to keep reserve estimates physical.