Producing time and Horner time ratio
Effective producing time before a build-up from the cumulative production and the last rate, the Horner time ratio (t_p + Δt)/Δt for the plot axis, and Agarwal's equivalent time.
t_p = 24 · N_p / q(t_p + Δt) / ΔtΔt_e = Δt · t_p / (t_p + Δt)The varying rate before shut-in is replaced by the last rate over the time t_p with the same cumulative production (Horner). If t_p is much longer than the build-up, the MDH plot of pressure against log Δt works too. The equivalent time Δt_e lets drawdown type curves be used on a build-up.
Source: Horner (1951); Earlougher, SPE Monograph 5 (1977), ch. 5; equivalent time: Agarwal, SPE 9289 (1980)
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Since start-up or since the last long shut-in that let the pressure recover.
Stabilized, in the same terms as N_p.
Unit converter for this formulaLiquid volume · Liquid rate · Time
- m³1
- 10³ m³0.001
- 10⁶ m³1·10⁻⁶
- L1,000
- bbl6.28981
- Mbbl0.00628981
- MMbbl6.28981·10⁻⁶
- ft³35.3147
- US gal264.172
- (t_p + Δt)/Δt — Horner time ratio–
- Δt_e — Agarwal equivalent time–
More in Build-up and drawdown
Skin factor from the semilog straight line of a pressure build-up curve.
Skin factor from the semilog straight line of a pressure drawdown curve.
Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in psi per log cycle.
Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in bar per log cycle.
Transmissibility kh/μ, flow capacity kh and permeability from the slope of the semilog straight line of a build-up or drawdown (radial flow).
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.