Phase 1 — Deep Gas Source (Primary Energy Input): Foundation of a Dynamic Multiphase Model for Subsurface Fluid Systems

Description (Abstract) This study presents Phase 1 of a unified dynamic multiphase model describing subsurface fluid systems. This phase defines the primary energy input of the system through deep-origin gas generation, including CO₂, CH₄, and H₂, produced by high-pressure and high-temperature processes within the Earth’s interior. At depths typically exceeding 5 km, the Earth functions as a high-energy reservoir where mantle degassing, metamorphic reactions, and deep fluid–rock interactions generate pressurized fluids. The resulting pressure gradient between deep and shallow formations initiates fluid migration and drives the evolution of hydrocarbon systems. The process is governed by fundamental physical relationships, including pressure differentials (ΔP = P_source − P_reservoir) and the system parameter Λ = P_flow / P_c, where fluid flow is controlled by the balance between driving pressure and geological resistance. At this stage, P_flow is approximately equal to the deep source pressure, emphasizing the dominant role of deep energy input. This phase establishes the system as energy-driven rather than purely material-driven, introducing a continuous and dynamic source of fluid generation. It provides a conceptual and physical foundation for subsequent phases, supporting sustained migration, hybrid biotic–abiotic interactions, and long-term system evolution.