Time to pseudo-steady state
How many hours after a well starts at a constant rate the pressure begins to fall at the same rate throughout the drainage area: to plan drawdowns that reach the boundaries and reservoir limit tests.
t_pss = t_DA · φ · μ · c_t · A / kHomogeneous reservoir with no-flow boundaries, constant rate. Until then the well does not feel the boundaries, which limits the semilog analysis of a drawdown. Lee's stabilization time t_s = 948 · φ · μ · c_t · r_e² / k (field units) corresponds to t_DA ≈ 0.08.
Source: Earlougher, SPE Monograph 5 (1977), ch. 2 and app. C
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Area per well: 16 ha for a 400 × 400 m pattern.
0.1 for a circle or square with the well at the centre; more for elongated areas and off-centre wells (Earlougher, app. C).
Unit converter for this formulaPermeability · Viscosity · Compressibility · Area · Time · Fraction and percent
- mD1
- D0.001
- µm²0.000986923
- 10⁻³ µm²0.986923
1 D = 0.9869 µm². Russian-language reports often give permeability in 10⁻³ µm², which is almost mD (1 mD = 0.9869 · 10⁻³ µm²).
- t_pss/24 — The same in days–
More in Test design
How far from the well the pressure transient has travelled during the test, and the hydraulic diffusivity: to choose the test duration and to judge whether the test will see the boundaries.
Wellbore storage coefficient from a moving liquid level and from fluid compression in a closed wellbore, and the time after which the build-up or drawdown reaches the semilog straight line of 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.