Rate transient analysis (RTA) or decline curve analysis (DCA) uses empirical models that enable a reasonable production forecast with minimum effort using only the well production history. Wells producing from conventional gas reservoirs typically reach boundary-dominated flow behavior in a matter of hours or days after which commonly used empirical models provide a match for rate decline behavior that enables a forecast for the well production and a reasonable estimate for the well expected ultimate recovery (EUR). For shale gas wells, the onset of boundary-dominated flow behavior may occur after several years on production, or even after several decades. Before that the well behavior will likely follow an easily forecasted transient trend, but EUR estimation based on a transient rate decline trend is likely to be overly optimistic and highly misleading.

Quantities provided by the RTA forecast are an estimate for the EUR and a corresponding estimate for the well production revenue, the latter given an assumed model for future gas prices. While RTA forecasts have been reasonable for wells in conventional reservoirs, they may be seriously overestimating the EUR in shale gas wells. This study uses RTA models to match rigorous analytical or numerical model trends to demonstrate the risks in misapplication of empirical models and offer insights on how easily to reduce the uncertainty in EUR estimates.

Synthetic data from shale gas wells will demonstrate a simple RTA process that is quick to apply and provides critical insights about the nature of their uncertainty.

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