How does the connectivity of open-framework conglomerates within multi-scale hierarchical fluvial architecture affect oil sweep efficiency in waterflooding?

摘要

We studied the effects on oil sweep efficiency of the proportion,hierarchical organization, and connectivity of high-permeability open-frameworkconglomerate (OFC) cross-sets within the multi-scale stratal architecture foundin fluvial deposits. Utilizing numerical simulations and the RVA/Paraviewopen-source visualization package, we analyzed oil production rate, waterbreakthrough time, and spatial and temporal distribution of residual oilsaturation. The effective permeability of the reservoir exhibits large-scaleanisotropy created by the organization of OFC cross-sets within unit bars, andthe organization of unit bars within compound bars. As a result oil sweepefficiency critically depends on the direction of the pressure gradient. Whenpressure gradient is oriented normal to paleoflow direction, the total oilproduction and the water breakthrough time are larger, and remaining oilsaturation is smaller. This result is found regardless of the proportion orconnectivity of the OFC cross-sets, within the ranges examined. Contrary toexpectations, the total amount of trapped oil due to the effect of capillarytrapping does not depend on the pressure gradient within the examined range.Hence the pressure difference between production and injection wells does notaffect sweep efficiency, although the spatial distribution of oil remaining inthe reservoir depends on this value. Whether or not clusters of connected OFCspan the domain does not affect sweep efficiency, only the absolute rate of oilproduction. The RVA/Paraview application allowed us to visualize and examinethese non-intuitive results.