This study presents Phase 7 of a unified dynamic multiphase model describing subsurface fluid systems, focusing on capillarity as the primary microscale mechanism controlling fluid flow. Capillarity represents the resistance encountered by fluids when entering and moving through pore spaces, governed by surface tension, wettability, and pore geometry. As fluid mobility decreases during earlier phases, migration becomes increasingly controlled by capillary forces rather than bulk pressure. At this stage, fluid movement depends on overcoming capillary entry pressure, making pore throat size and fluid–rock interactions critical determinants of flow behavior. Capillary pressure is described by Pc = (2σ cosθ) /r, linking fluid behavior to surface tension, contact angle, and pore radius. This establishes a threshold system in which flow occurs only when the driving pressure exceeds capillary resistance. The relationship is integrated into the global model through the parameter Λ = Pflow / Pc, defining conditions for continued migration (Λ > 1) or flow restriction and trapping (Λ < 1). This phase represents a fundamental transition from macroscopic pressure-driven flow to microscopic pore-scale control. The system becomes highly selective and non-linear, where small variations in pore geometry produce significant changes in fluid behavior. By introducing threshold-dependent flow and pore-scale physics into the framework, this phase provides a physical basis for selective trapping, reservoir boundaries, and the localization of hydrocarbon accumulations. This publication is part of the research series: “A Dynamic Multiphase Model for Hydrocarbon and Hydrothermal Systems” It represents Phase 7 in a structured 13-phase framework describing the evolution of subsurface fluid systems from deep energy generation to accumulation. This phase defines the pore-scale threshold controlling fluid entry and trapping, linking microscopic structure to macroscopic reservoir formation.
Kujtim gjoka Gjoka (Fri,) studied this question.