Pore scale applications of Phase-field Lattice Boltzmann Methods for underground CH4, H2 and CO2 storage

The design of sustainable large-scale underground energy storage systems relies on accurate reservoir dynamic modelling. Key macroscopic parameters, such as critical saturations, capillary pressure, and relative permeabilities, are strongly influenced by pore-scale multiphase flow phenomena and trapping mechanisms. The analysis of multiphase flow behavior at the pore scale can therefore improve reservoir characterization and support engineering applications, including underground storage of natural gas (UGS), hydrogen (UHS), and carbon dioxide. This study investigates numerical modelling of imbibition and drainage processes, representative of withdrawal and injection scenarios, using the Lattice Boltzmann Method (LBM). Owing to its inherent parallel structure and flexibility in handling complex geometries, LBM provides an efficient framework for simulating multiphase flow in porous media. However, previous studies have often applied LBM to simplified porous geometries or relied on boundary conditions that were not designed to handle phase transitions at the outflow boundary in evolving multiphase systems. In this work, the open-source parallel library OpenLB is tailored and adapted to simulate two-phase flows governed by the Allen–Cahn equation in two-dimensional porous domains. The proposed developments overcome previous limitations by enabling the simulation of more realistic geometries and by implementing outflow boundary conditions that allow phase interfaces to dynamically cross the outlet. The simulated domains were designed to reproduce physical 2D micromodels (Rock-on-a-Chip) representative of reservoir rocks, focusing on H2, CH4, and CO2–brine systems, with brine representing formation water. After validation against laboratory experiments, the numerical framework is intended to extend the analysis to reservoir conditions that are difficult to reproduce experimentally.