Reactive Transport and Péclet Number Analysis of Hydrogen Flux Pathways in Uniform Clay Matrix: Implications for Underground Storage

Abstract

Reactive transport modeling in unique chamosite, illite, and kaolinite monomineralic clay reservoirs was performed to predict spatial and mineralogical control on H_2(aq) distribution and flow dynamics at simulated underground hydrogen storage pressure and temperature conditions in high permeability depleted oil reservoirs and lower permeability sandstones. Results are normalized against simulations performed in pure quartz for comparative purposes and to serve as a benchmark for H₂ storage in sandstone or quartz-arenite reservoirs. Isobaric and isothermal condition results indicate that Péclet numbers increase with volume rate of injected fluid. Advection-mediated transport is ubiquitous for injection rates between 0.01 and 1.0 L per second, although diffusion-mediated transport is prevalent in the center of the RMT block at 0.001 L per second injection. Source/sink term and Péclet number analysis indicate that the effect of mineralogy on H_2(aq) transport is small. Flow velocities in kaolinite are typically the fastest, but chamosite Péclet numbers are greatest. This suggests that kaolinite favors diffusion, chamosite favors advection, and illite is intermediate. A more accurate reflection of underground hydrogen storage conditions incorporating temperature and pressure gradients, permeability anisotropy, and mineralogical heterogeneity shows a decrease in Péclet numbers proportional to distance from injection well. Thus, along the reservoir-caprock boundary and in the absence of cushion gas, H_2(aq) loss through diffusion is probable. Although quantitative flow regime analysis cannot be determined at many grid point locations due to uniform H_2(aq) concentration, these locations are very likely diffusion dominant.