Radius of investigation and diffusivity
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.
χ = k / (φ · μ · c_t)r_i = 2 · √(χ · t)The distance a noticeable pressure disturbance has reached in an infinite homogeneous reservoir; in field units (ft, mD, h, cP, psi⁻¹) it is r_i = √(k · t / (948 · φ · μ · c_t)). Authors define it differently by tens of percent, so it is an order-of-magnitude estimate: to see a boundary at a distance L with confidence, test well beyond the time when r_i = L.
Source: Lee, Well Testing (1982): r_i = √(k · t / (948 · φ · μ · c_t)); diffusivity: V. N. Shchelkachev
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
For a build-up, the shut-in time Δt (with t_p ≫ Δt).
Unit converter for this formulaPermeability · Viscosity · Compressibility · Time · Length · Area · 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).
- χ — Hydraulic diffusivity–m²/s
- π·r_i² — Investigated area–
More in Test design
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.
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.
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.