In order to understand waterflood performance in low permeability, naturally fractured Spraberry Trend Area reservoirs, an integrated study of imbibition waterflooding has been performed. In this study, oil production during imbibition waterflooding in naturally fractured reservoirs has been mathematically analyzed on the basis of the rate law that governs mass transfer. Analytical models for decline curve analysis based on imbibition theory have been developed. Imbibition and capillary pressure experiments have been conducted in the laboratory using reservoir crude oil, synthetic reservoir brine, and low-permeability reservoir cores under room and reservoir conditions. Remarkable consistency has been observed using experimental data to scale-up and match reservoir performance. It is found that slow imbibition of water into the weakly water-wet rock matrix is the limiting step for oil recovery during waterflooding. This study suggests that better waterflooding should be sought in areas of high matrix permeability, high fracture intensity, and significant oil saturation.

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