This paper describes a methodology for determining ultimate recovery (EUR) using production data. It based on the premise that ratio of remaining reserve (R) to annual production (P) versus time remains constant, if the correct EUR is considered for analysis. The R/P ratio versus time shows upward trend for higher EUR and the trend exhibits downward trend for lower EUR. The correct EUR results in a horizontal line of R/P versus time. Thus, the EUR can be determined using trial error or optimization process which can be done simply in spreadsheets. In this paper, we provide a theoretical justification of the above method using analytical method.

Sensitivity analysis of the R/P technique applicability is done and it was found that the plot of R/P and its derivative are very useful tool for EUR estimation. We present the application of the technique with both synthetic and field data sets including oil, gas field and water flooded reservoirs. The results compare favorably with Arp’s Decline Curve Analysis (DCA), Log(WOR) versus cumulative production as well as dynamic models which instil confidence on the robustness of the proposed methodology.


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