Research on the storage performance evaluation and economic prediction of catalyzed green methanol underground

Underground energy storage is widely believed as a major strategy for achieving low-carbon emission. Cooperative storage of carbon dioxide (CO₂) and hydrogen (H₂) is a potential efficient energy storage mode which not only achieves hydrogen storage, but also carbon sequestration. Due to characteristics of low molecular weight and gaseous phase, underground hydrogen owns a low energy density, which retards ultimate storage efficiency. Based on above reasons, a new concept of underground methanol storage is proposed. The primary principle involves catalyzing the reaction between injected CO₂ and H₂ to produce methanol, where methanol is in the liquid phase and CO₂ and H₂ are in the gas phase. This paper is motivated to investigate flow mechanisms of liquid methanol underground. A two-phase flow simulator solved by implicit pressure explicit saturation (IMPES) method is developed to characterize pressure profile and saturation distribution of underground methanol. Then, incompressible and slightly compressible flows are discussed in detail and a critical compressible flow coefficient is investigated. Moreover, sensitivity analyses on capillary pressure and relative permeability are conducted to demonstrate that higher capillary pressure and relative permeability can induce wider pressure and saturation spreading. Finally, Multi-Objective Particle Swarm Optimization (MOPSO) algorithm is used to achieve holistic process optimization of system performance and cost analysis.