Despite the widespread application of reservoir simulation to forecast waterflood performance, petroleum engineers still need simple production decline analysis methods to forecast oil production and estimate ultimate oil recovery from the production history data. For pressure depletion recovery processes, Arps proposed an empirical model and Fetkovich validated the Arps model based on the transient and semi-steady state solutions. However, for waterflood reservoirs, reservoir pressure is generally maintained and oil production decline is mainly due to the reduction of oil saturation and oil relative permeability. This study explains the inconsistencies when the Arps production decline model is used as a framework to forecast the waterflood recovery process. An analytical oil production forecast method specifically for waterflood based on the Buckley-Leverett theory has been developed. This study compares forecasts by the new method with field performance data and reservoir simulation results. These comparisons demonstrate the straightforward, convenient and accurate application of the new forecast method for waterflood reservoirs.
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