Duong Decline Forecast
Spreadsheet
27 rows x 3 columns
| A | B | C | |
|---|---|---|---|
| 1 | Duong Decline Forecast - Unconventional Well | ||
| 2 | Inputs | ||
| 3 | Decline Constant (a) | 1 | - |
| 4 | Decline Exponent (m) | 1.35 | - |
| 5 | Initial Rate (q1) | 15000 | bbl/month |
| 6 | Infinite Rate (q_inf) | 0 | bbl/month |
| 7 | Economic Rate (q_econ) | 60 | bbl/month |
| 8 | Production Forecast | ||
| 9 | t (months) | q (bbl/month) | Np (Mstb) |
| 10 | 1 | 15000 | 15 |
| 11 | 3 | 8473.785128 | 37.34144684 |
| 12 | 6 | 5054.261458 | 56.77562089 |
| 13 | 12 | 2754.473305 | 78.87388809 |
| 14 | 24 | 1398.505602 | 102.0820509 |
| 15 | 36 | 916.0484587 | 115.5917462 |
| 16 | 48 | 671.6759465 | 124.9785456 |
| 17 | 60 | 525.2664126 | 132.0942214 |
| 18 | 120 | 238.6507261 | 152.9880265 |
| 19 | 180 | 148.1734123 | 164.2056757 |
| 20 | 240 | 105.0528977 | 171.6695278 |
| 21 | 360 | 64.23854156 | 181.4696695 |
| 22 | |||
| 23 | EUR Summary | ||
| 24 | EUR (to q_econ) | 182.7515393 | Mstb |
| 25 | 30-Year Cum | 181.4696695 | Mstb |
| 26 | 5-Year Cum | 132.0942214 | Mstb |
| 27 | 10-Year Cum | 152.9880265 | Mstb |
Description
Decline curve forecast using the Duong model, specifically designed for unconventional reservoirs exhibiting transient linear flow. The Duong model captures the power-law behavior common in tight oil and shale gas wells.
Parameters:
- qi: Initial production rate
- a: Decline constant (typically 1.0-2.0)
- m: Decline exponent (typically 1.0-1.5)
- q_inf: Infinite time rate (often set to 0)
Picking a and m: EUR is bounded only because m > 1, and it is far more sensitive to m than the ranges above suggest. For q_inf = 0 the ultimate is (q1/a)·exp(a/(m-1)), so the exponent a/(m-1) sets everything — and the share of that ultimate recovered by time t is exp(-(a/(m-1))·t^(1-m)). At a=2.0, m=1.2 the exponent is 10, the ultimate is ~165 MMbbl, and 30 years of production captures under 5% of it. The values here (a=1.0, m=1.35) put the exponent near 2.9, so the 30-year forecast below captures about 70% of the ultimate and the economic limit is reached just past the end of the table. If you fit a and m to data, check the forecast window against the EUR before trusting either.
Units: rates are bbl/month against a time column in months, so the cumulative column is a true volume (shown as Mstb). The Duong functions are unit-agnostic — rate and time must share the same time base.
How to use this blueprint
- In Excel, go to the Petroleum Office ribbon tab and click Blueprint Manager
- Search for Duong Decline Forecast
- Click on the blueprint to preview
- Click Insert to place it into your worksheet. Modify the input values to match your data.