Paste monthly production · fit Arps qi, Di, b · forecast EUR to an economic limit
Zero-rate (shut-in) months are skipped in the fit but keep their place in time; a blank cell between months is read as zero. Commas inside numbers (1,234) are read as thousands separators, so separate columns with tabs or spaces. At least 6 producing months are needed; 12+ is much better.
How the economics tools fit together: NPV, payback, tariffs and operating costs
Choose the decline model (exponential, hyperbolic or harmonic) and adjust qi, the initial decline Di and the exponent b to minimize the difference between the model rate and the observed rate. This tool minimizes the squared error of the natural log of rate, so early high-rate months do not dominate the fit.
b = 0 is exponential decline, b = 1 harmonic, and values between are hyperbolic. Conventional wells often fit b between 0 and 0.5; unconventional wells often fit 1 or higher during transient flow. Because a large b overstates the long tail, practitioners cap b (this tool defaults to 1.5) and apply a terminal exponential decline.
Nominal decline Di is the instantaneous rate in the equations. Effective decline is an annual percentage, defined two ways (SPEE REP 6). This tool reports secant effective decline, the actual drop in rate over the first year: De = 1 - (1 + b*Di)^(-1/b), or 1 - exp(-Di) for exponential. Tangent effective decline is 1 - exp(-Di) for any b.
At least 6 producing months, but 12 to 24 or more is far better. With a short history many combinations of b and Di fit equally well and the EUR forecast is uncertain.
No. It is a screening forecast from a curve you fit to past production. Reserves classification requires the full SPE-PRMS process, reservoir data and economic assumptions.