Abstract

Though it is the oldest and most common of the six engineering techniques for the determination of reserves, both the theory and practice of decline curves continue to suffer from widespread misunderstanding and lackluster implementation. Decline curve analysis is not a curve-fitting exercise, and it should not be limited to a single rate-time graph of each well in isolation, much less just any rate-time graph created by the sloppy defaults of most graphing programs.

Decline curve analysis is an exercise in seeing, understanding and predicting the reservoir and operational dynamics. A practitioner should be adept at creating graphs from which she can identify reservoir dynamics, trace trends as precisely as possible and thus anticipate likely future behavior. Graphs should show only relevant data and show it clearly, without distraction. Multiple graphs examined in parallel often lead to better insights, though the graphs and their contents may vary among situations. Besides drawing on general experience, an evaluator often needs to examine the nearest and best analog production trends to make good forecasts. To do all this, the evaluator needs to be able to discriminate operational changes and to understand the uncertainty of the production data itself.

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