Calculator
Example Data Table
| Example | Pr (psi) | Pwf_test (psi) | q_test (stb/d) | Model | AOF (stb/d) |
|---|---|---|---|---|---|
| Well A | 3000 | 1500 | 800 | Vogel | ≈ 1143 |
| Pwf (psi) | q (stb/d) |
|---|---|
| 3000 | 0 |
| 2000 | ≈ 514 |
| 1500 | 800 |
| 1000 | ≈ 971 |
| 0 | ≈ 1143 |
Formula Used
Linear PI (Darcy): q = J(Pr − Pwf). Use for undersaturated oil or near-linear inflow.
Vogel: q = qmax[1 − 0.2(Pwf/Pr) − 0.8(Pwf/Pr)²]. Common for solution-gas drive reservoirs.
Fetkovich: q = qmax[1 − (Pwf/Pr)ⁿ]. Fits a wide range of curvatures using exponent n.
PI from properties (oilfield units): J = (0.00708·k·h)/(μ·B·(ln(re/rw)+s)). Inputs: k(mD), h(ft), μ(cP), B(rb/stb), re(ft), rw(ft), skin(s).
How to Use This Calculator
- Select an IPR model that matches your reservoir behavior.
- Choose consistent pressure and flow units for all fields.
- Enter reservoir pressure Pr and optional target Pwf.
- Pick a parameter method: test point, direct entry, or properties.
- Press Calculate Curve to generate the IPR table and plot.
- Use the export buttons to download CSV or PDF summaries.
Data Inputs That Drive Curve Shape
Reservoir pressure Pr sets the x‑axis limit and the curve ceiling. Typical Pr ranges from 1,500–6,000 psi, while target Pwf often sits 20–60% below Pr to protect drawdown. A test point (q_test at Pwf_test) anchors the model and should be taken after rate and pressure settle. Use 8–60 points to balance smoothness and size.
Choosing a Model for the Drive Mechanism
Linear PI assumes near‑Darcy behavior: q = J(Pr − Pwf). It is strongest when pressure drawdown is modest and inflow is close to straight. Vogel better matches solution‑gas drive curvature and commonly yields a higher AOF than linear for the same test. Fetkovich adds flexibility with exponent n; n near 1 trends linear, while n between 2 and 4 increases curvature for tighter or multiphase systems.
Interpreting AOF and Operating Window
AOF (q at Pwf = 0) is a theoretical upper bound, not an operating target. Engineers typically select an operating Pwf that avoids sanding, coning, or pump intake issues, then read the expected rate at that point. If target Pwf is 1,000 psi and Pr is 3,000 psi, the pressure ratio is 0.33, which can materially change Vogel or Fetkovich flow predictions compared with linear PI.
Quality Checks and Sensitivity
A practical check is reproducing the test point: the derived constants should predict q_test within a few percent if inputs are consistent. Sensitivity can be run by shifting Pr ±5% to reflect gauge uncertainty or datum corrections. In the PI‑from‑properties method, k and skin dominate: doubling k doubles J, while increasing skin raises ln(re/rw)+s and reduces J. Keep re > rw and ensure the denominator stays positive.
Reporting, Exports, and Engineering Decisions
The exported CSV supports plotting quickly in spreadsheets, while the PDF summarizes assumptions for reviews. Use the curve to compare candidate choke settings, pump speeds, or tubing changes by translating surface constraints into target Pwf. When tracking depletion, regenerate curves with updated Pr and repeatability tests to quantify productivity changes over time. Combine IPR with outflow performance for nodal analysis and robust rate forecasts.
FAQs
1) What does this calculator produce?
It generates an IPR table and curve that relates bottomhole flowing pressure to rate. It also reports AOF, derived parameters, and optional rate at a target Pwf for quick screening.
2) How do I choose between Linear, Vogel, and Fetkovich?
Use Linear PI for near‑single‑phase, small drawdown behavior. Use Vogel for solution‑gas drive oil. Use Fetkovich when you need adjustable curvature via exponent n to match test behavior.
3) Why is AOF shown at Pwf = 0?
AOF is a standardized reference point for comparing wells and models. It is theoretical, because real wells hit equipment limits, multiphase constraints, or sand control requirements before reaching zero bottomhole pressure.
4) Can I compute J from properties for any model?
The properties method computes J for the Linear PI model only. It uses k, h, μ, B, re, rw, and skin in an oilfield‑units correlation. For Vogel or Fetkovich, use a test point or direct AOF.
5) My curve looks wrong. What should I check first?
Confirm Pr and Pwf are in the same unit and that Pwf_test and target Pwf are not greater than Pr. Verify q_test is stabilized. For properties, ensure re > rw and ln(re/rw)+skin remains positive.
6) When should I export CSV versus PDF?
Export CSV when you want to plot, fit, or merge points in spreadsheets and simulators. Export PDF when you need a compact summary of inputs, assumptions, and key results for review or sharing.