Reserves and Forecasting · Module R3
Arps Decline Curve Analysis
The Arps family of decline curves and how to choose among them on evidence. It covers the role of the b-exponent and its physical meaning, the two ways of quoting a decline rate, why goodness-of-fit alone favours over-flexible models, and how to hand a fitted decline to an economic model.
- Level
- Intermediate
- Position
- Module 3 of 8
- Video
- About 18 minutes, narrated
- Format
- Narrated video lesson with captions and slide reading view; with the certified option, a quiz whose pass unlocks the next module.
What the module covers
- One equation, three decline shapes
- What the b-exponent says about the reservoir
- Nominal and effective decline conversions
- R² versus the small-sample AICc
- Re-basing a fitted decline to an effective date
Learning outcomes
After the module you should be able to:
- Choose a decline model on evidence, not on the highest R².
- Fit and compare exponential, hyperbolic and harmonic models
- Convert between nominal and effective decline
- Explain why a higher R² can mean a worse forecast
A short preview
Decline rates are quoted two ways and mixing them is a common unit error. For an exponential decline, an effective annual decline De and a nominal rate D are linked by De = 1 − e^(−D). A nominal 40 percent per year is therefore an effective 33 percent: the rate falls by a third over the year, not by 40 percent. Hyperbolic declines need the b-exponent in the conversion as well, so state which convention a number uses whenever it changes hands.
Who it is for
Reservoir and production engineers, petrophysicists and geoscientists who estimate, review or report reserves and production forecasts.
Prerequisites: None required; working familiarity with production data and volumetrics helps.
Take the module in the Learning Hub
Reserves and Forecasting: Specialty course, sold separately: eight modules from PRMS classification and decline curves to type wells, material balance, aggregation and the reserves report. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.