A novel interwell connectivity evaluation method for waterflooding reservoir using oil-water production performance

Abstract

To address the issues that the existing connectivity evaluation models can only predict liquid production rate and the widely-used fractional-flow equations are not efficient to represent the water-producing characteristics in the whole water-cut variation period accurately, a novel connectivity evaluation method for waterflooding reservoir is established by using injection and production data. This developed model discretizes the reservoir into a series of production-based reservoir control volume. By coupling the producer-based capacitance-resistance model (CRMP) with a segmented water fraction-flow equation to obtain liquid production rate and water-cut, oil-water production data of each well can be further determined. Finally, the estimated parameters including connectivity, time constant and drainage volume of each producer are determined by history matching the measured production data with the newly developed Stochastic Simplex Approximate Gradient (StoSAG) optimization algorithm. Case studies show that, compared with the EnKF algorithm and the traditional projected gradient algorithm, the robustness of the ensemble-based StoSAG optimization procedure is higher. Moreover, the segmented water fractional-flow equation can achieve better dynamic matching and prediction effect of the measured production data than that of the single Koval fractional-flow model, which fully validate the reliability of the proposed interwell connectivity evaluation method and provides the theoretical basis for the actual applications in strongly-heterogeneous waterflooding reservoirs.