Confidently establishing single well and/or aggregated production profiles, particularly estimated ultimate recovery (EUR), is both an important and challenging process in unconventional reservoirs. Numerous papers have proposed forecasting techniques, but four fundamental approaches dominate:

  • Empirical decline curve analysis (DCA), such as multisegment Arps, the modified stretched exponential production decline (YM-SEPD) model, Duong's method, and power-law methods.

  • Rate-transient analysis (RTA), which can include corrections for special dynamic mechanisms (e.g., stress-sensitivity, multiphase flow, adsorption/desorption).

  • Numerical simulation for history-matching and forward modeling.

  • Volumetrically determining in-place resources based on geological data and then applying a recovery factor deemed suitable for the reservoir system and depletion scheme.

Each of these approaches can be implemented using either probabilistic or single-point estimates. Seidle et al. (2016) recently outlined recommended methodologies to accurately forecast time-series volumes and ultimate recovery in unconventional systems. A key recommendation in Seidle et al. (2016) is that the multiple approaches listed previously should be reconciled to establish confidence in forecasts and ultimate recovery estimates. However, Seidle et al. (2016) does not detail the means to achieve this goal. This paper establishes a methodology/workflow to reconcile the different types of empirical DCA methods, which should serve as a starting point for the ultimate goal of reconciling the four fundamental approaches listed.

This paper compares and contrasts the DCA methods applied to various field cases in prominent Canadian [Western Canadian Sedimentary Basin (WCSB)] and US unconventional (oil and gas) plays (Bakken, Barnett, Cadomin, Eagle Ford, and Niobrara). Data sets are selectively chosen based on data quality and history length to increase confidence in the appraisal of the DCA approach. Hindcasting is applied to validate the results and conclusions.

From analysis of a number of wells in different types of reservoirs, a new workflow (methodology) is proposed and validated with hindcasting that allows practically and accurately reconciling EURs based on various empirical methods.

This manuscript is the first paper to discuss systematic reconciliation of EURs from varying approaches for horizontal wells in tight/shale reservoirs.

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