Architecture-controlled remaining oil distribution in terminal fan and beach-bar deposits: an integrated 3D modeling analysis from the Paleogene Dongpu Depression, China

Sandstone architecture governs remaining oil distribution in high water-cut oilfields. This study presents a novel comparative analysis of two distinct sedimentary systems—terminal fan and shore-shallow lacustrine beach-bar deposits—in the Weicheng Oilfield, to establish genetically linked architecture-based models of remaining oil distribution. It elucidates the genesis and distinguishing features of dominant architectural elements in these deposits and demonstrates how their structural differences lead to contrasting mechanisms of remaining oil entrapment. The architecture of terminal fan is relatively simple and dominated by contrasts in unit types and physical properties. This results in uneven sweep efficiency during water flooding, with preferential channeling along high-permeability intervals and directions. Consequently, remaining oil follows a "property-contrast controlled" pattern. In contrast, beach-bar sandstones exhibit compartmentalized flow units governed by sandstone connectivity and spatial architecture. Variably continuous seepage barriers restrict both vertical and lateral sweep, yielding a "spatial-morphology controlled" remaining oil distribution. The comparative approach adopted here provides new insights into the remaining oil prediction in diverse environments. The models directly inform oilfield development by linking architectural styles to specific challenges, guiding targeted infill drilling, conformance control, and tailored recovery strategies. They demonstrate how deposition-specific models improve recovery efficiency and reduce risks in high water-cut reservoirs.