Phase 8 — Barrier Network (Multiscale Trapping System): Distributed Flow Restriction in a Dynamic Multiphase Framework

This study presents Phase 8 of a unified dynamic multiphase model describing subsurface fluid systems, focusing on barrier networks as multiscale mechanisms controlling fluid trapping. Barrier networks are defined as the spatial distribution of multiple interacting flow restrictions, including capillary, lithological, and structural barriers. Following the onset of capillary control in earlier phases, fluid migration is no longer governed by a single threshold but by a complex network of barriers operating across multiple scales. These include pore-scale capillary thresholds, layer-scale low-permeability strata, and large-scale structural features such as faults and folds. The interaction of these barriers produces a distributed and dynamic trapping system in which fluid flow becomes fragmented, redirected, and locally accumulated. Instead of a single trapping point, the system develops multiple zones of partial blockage and progressive accumulation. Flow behavior is governed by local and network-level conditions, where fluid movement depends on the relationship between driving pressure and cumulative resistance across barriers. As barrier density increases, effective flow decreases, and the system transitions toward localized trapping conditions, represented by decreasing values of the parameter Λ = Pflow / Pc. This phase introduces a multiscale perspective on trapping, transforming the concept of reservoirs from simple, well-defined structures into complex, heterogeneous systems shaped by interacting barriers. It provides a framework for explaining irregular reservoir geometries, partial trapping, leakage, and the variability observed in natural systems. This publication is part of the research series: “A Dynamic Multiphase Model for Hydrocarbon and Hydrothermal Systems” It represents Phase 8 in a structured 13-phase framework describing the evolution of subsurface fluid systems from deep energy generation to accumulation. This phase introduces multiscale trapping through interacting barrier networks, explaining how fluid flow becomes fragmented and progressively localized within the subsurface.