Productivity Index Calculator for Engineering Wells

Calculator Inputs

Calculation Mode

Fluid Type

Unit System

Reservoir Pressure

Flowing Bottomhole Pressure

Measured Flow Rate

Known Productivity Index

Target Rate

Future Flowing Pressure

Test Name

Notes

Plotly Graph

This inflow-style chart shows how predicted rate changes as flowing pressure changes while reservoir pressure remains fixed.

Example Data Table

Case	Reservoir Pressure	Flowing Pressure	Rate	Drawdown	Productivity Index
Well A	3200 psi	1800 psi	900 bbl/day	1400 psi	0.6429 bbl/day/psi
Well B	3500 psi	2100 psi	980 bbl/day	1400 psi	0.7000 bbl/day/psi
Well C	3000 psi	1700 psi	715 bbl/day	1300 psi	0.5500 bbl/day/psi
Well D	2800 psi	1500 psi	624 bbl/day	1300 psi	0.4800 bbl/day/psi

Formula Used

PI = q / (Pr - Pwf)

PI is productivity index, q is flow rate, Pr is reservoir pressure, and Pwf is flowing bottomhole pressure.

Rate form: q = PI × (Pr - Pwf)

Pressure form: Pwf = Pr - (q / PI)

How to Use This Calculator

Select the required calculation mode.
Choose your fluid type and unit system.
Enter reservoir pressure and flowing pressure.
Add either measured rate or known productivity index.
Submit the form to show results above the form.
Review the graph, metrics, and export options.

Frequently Asked Questions

1. What does productivity index mean?

Productivity index measures how easily a well delivers fluid for a given pressure drawdown. Higher values usually indicate better inflow performance and stronger deliverability.

2. Why is pressure drawdown important?

Pressure drawdown is the difference between reservoir pressure and flowing pressure. It is the driving force behind flow, so PI calculations depend directly on it.

3. Can I use metric units?

Yes. Select metric units to interpret inputs as kPa and m³/day. The displayed productivity index unit changes automatically with the selected system.

4. When should I calculate rate instead of PI?

Calculate rate when you already know PI and want to test a new operating pressure. This is useful for quick production planning scenarios.

5. What does a low productivity index suggest?

A low value may suggest formation damage, completion restrictions, poor permeability, or limited pressure support. It signals weaker well inflow behavior.

6. Can this calculator forecast future performance?

Yes. The forecast mode estimates a future rate using the current PI and a new flowing pressure. It provides a fast linear estimate.

7. Is the relationship always perfectly linear?

No. This tool uses a simple linear PI model. Real wells, especially gas wells or damaged wells, can deviate from linear inflow behavior.

8. What data gives the most reliable result?

Use stabilized pressure and rate measurements from a representative well test. Reliable field measurements improve PI estimates and forecast confidence significantly.