DFIT & step-down interpreter
Two free Live+ diagnostics: classify a shut-in pre-closure regime and invert step-down plateaus into perf Cd + near-wellbore tortuosity. No signup, nothing stored. This page does not pick ISIP, closure, G or efficiency — use the full DFIT page for those.
Pre-closure regime classifier
Fit is log|dP/dt| vs log t (derivative slope): ≈0 → wellbore storage, −0.5 → fracture-linear (√t), −0.75 → bilinear, −1 → pseudoradial. Compare against your G-function to lock closure.
One file with the inputs as typed, each result labelled solved or estimate, the residual, every refusal, and a fingerprint. Anyone can check it at /verify without an account.
Step-down inverter (perf Cd + NWB tortuosity)
Model: Δpperf=0.2369·ρ/(Cd²·n²·d⁴)·q² + ΔpNWB=K·qn.
Field step-down work reports the near-wellbore exponent near 0.5 before slurry and near 1.0 after proppant placement, so the phase changes the fit — state it rather than inheriting a default.
Healthy K_nwb < 15, elevated 15–60, severe ≥ 60 psi/bpm0.5.
- Cd_eff is a lumped coefficient for the assumed geometry: it moves with the assumed shot count, perf diameter and slurry density as well as with the perforations themselves.
- A falling Cd_eff is consistent with fewer effective open shots — blockage, bridging or unbroken clusters — under the assumed geometry.
- Erosion works the other way: published erosion modelling reports the hole enlarging and the flow coefficient increasing, so a rising Cd_eff (or an apparent shot count above the design count) is the erosion signature.
- Un-removed wellbore friction above the perforations is absorbed into K_nwb, which can shift the apparent Cd; correct pipe friction before reading Cd as a perforation property.
- Treat both Cd_eff and open shots as an uncertainty range across the exponent and geometry assumptions, not as a single measured value.
| n | Cd_eff | Open shots | K_nwb [psi/bpm^n] | RMS [psi] |
|---|---|---|---|---|
| 0.50 | 0.310 | 14.6 | 56.67 | 52.4 |
| 1.00 | 0.350 | 16.5 | 13.17 | 29.3 |
Changing only the exponent moves Cd_eff by 0.040 and open shots by 1.9. The estimate is comparatively insensitive to the exponent choice.
- Cd and open-shot count are assumption-dependent alternatives fitted from the same q² term — they are not two independent measurements. Changing the assumed shot count moves Cd, and the reverse.
- Only the total pressure loss is observed. The split between perforation friction and near-wellbore tortuosity follows the assumed q² / q^n form, not a direct measurement of either.
- Wellbore friction above the perforations is not corrected here; any un-removed pipe friction is absorbed into K_nwb.
One file with the inputs as typed, each result labelled solved or estimate, the residual, every refusal, and a fingerprint. Anyone can check it at /verify without an account.