Phase equilibrium modeling advances subsurface energy transition for a carbon-resilient future

Subsurface energy transition aims to mitigate climate change impacts by reducing carbon emissions while addressing energy needs through utilization of sustainable subsurface resources. It involves harnessing underground space for energy production and storage, encompassing strategies like sustainable recovery of unconventional resources, carbon capture, utilization and storage (CCUS), H 2 geological storage and geothermal development, etc. A swift and scalable deployment of the subsurface energy transition portfolios necessitates significant numerical endeavors wherein modelling the complex phase phenomena remains a practical challenge. Herein this paper examines literature in numerical phase equilibrium calculations, focusing on advancements in thermodynamic models and multiphase flash calculations, particularly in the context of energy transition in the subsurface domain for a carbon-resilient future, and the review is focused on vapor -liquid equilibrium. Methodologies for phase stability test, adjustments in phase behavior based on thermodynamics, developmental process of algorithms for phase equilibrium calculations, and applications in the energy field are covered. The application of phase behavior numerical calculation in developing unconventional oil and gas resources, CCUS, H 2 geological storage and geotherm are highlighted. It is found that although many EoSs merged with various modified parameters under certain conditions, which based on PR or other EoSs from last century, there is no such simplified representative equation with a broader application range. Moreover, lacking experimental results limits the verification of phase equilibrium calculation and data-driven model training. Thus, the phase equilibrium in subsurface energy still needs efforts to engage. In addition, methodological gaps and potential development paths are identified and suggested, aims to shed light upon the development in phase equilibrium calculations in the context of subsurface energy transition for promoting a carbon-conscious world. • Provides a comprehensive review of phase equilibrium modeling for subsurface energy transition applications. • Identifies key methodological gaps: the lack of a broadly applicable EoS and insufficient data fordata-driven methods. • Integrates classical thermodynamic approaches with emerging data-driven techniques under extreme subsurface conditions. • Proposes actionable research pathways to advance phase equilibrium modeling for subsurface energy technologies.