A document by Jiangzhi Chen. Click on the document to view its contents.

Storing \ce{CO2} in sub-seabed sediment is a promising \ce{CO2} sequestration method to reduce the atmospheric \ce{CO2} concentration and mitigate climate change, with the advantage of self-sealing capability due to formation of \ce{CO2} hydrate in the sediment pore space. Above the sequestration site, enhanced \ce{CO2} migration and supersaturation lead to a zone of coexisting gaseous, hydrate and aqueous phases of \ce{CO2} where curved surfaces of bubbles and hydrate crystals shift the phase equilibria, enabling fast development of the self-sealing capability due to permeability reduction by both hydrates and entrapped bubbles. We simulate the three-phase zone in a shallow seabed using a Monte Carlo method in packed synthetic mono-dispersed spherical sediment grains, and analyze its variations due to temperature and pressure perturbations. Our work demonstrates the difference between \ce{CO2} hydrate-bearing sediment layer and methane hydrate reservoir, and provides insight into the formation mechanisms of the self-sealing cap above sequestration sites.Updated version published as Jiangzhi Chen, Shenghua Mei,Gas-saturated carbon dioxide hydrates above sub-seabed carbon sequestration site and the formation of self-sealing cap,Gas Science and Engineering,Volume 111,2023,204913,ISSN 2949-9089,https://doi.org/10.1016/j.jgsce.2023.204913. 

An unusual salt-rich (SR) and salt-poor (SP) fluid immiscibility (FFI) could occur in a variety of hydrothermal fluids. The segregation of SR fluid from SP fluid provides a potential mechanism for substantial mass enrichment during some ore forming processes. However, the physical properties of SR and SP fluids, which determine the hydrodynamic behaviors of unmixed fluids, have not been well constrained. This study adopted in situ optical observation, quantitative Raman analysis, and the mass conservation law to derive the density of the SR and SP fluids. On this basis, falling sphere viscometry was employed to determine the viscosity of the SR fluid. Results showed that SR fluid exhibited an obviously higher density but comparable viscosity to SP fluid, favoring its high mobility and strong tendency to segregate from SP fluid. Consequently, the FFI could contribute tremendously to mass enrichment during fluid evolution.

Flow through partially frozen pores in granular media containing ice or gas hydrate plays an essential role in diverse phenomena including methane migration and frost heave. As freezing progresses, the frozen phase grows in the pore space and constricts flow paths so that the permeability decreases. Previous works have measured the relationship between permeability and volumetric fraction of the frozen phase, and various correlations have been proposed to predict permeability change in hydrology and the oil industry. However, predictions from different formulae can differ by orders of magnitude, causing great uncertainty in modeling results. We present a floating random walk method to approximate the porous flow field and estimate the effective permeability in isotropic granular media, without solving for the entire flow field in the pore space. In packed spherical particles, the method compares favorably with the Kozeny-Carman formula. We further extend this method with a probabilistic interpretation of the volumetric fraction of the frozen phase, simulate the effect of freezing in irregular pores, and predict the evolution of permeability. Our results can provide insight into the coupling between phase transitions and permeability change, which plays important roles in hydrate formation and dissociation, as well as in the thawing and freezing of permafrost and ice--bed coupling beneath glaciers.

Freezing in porous media is associated with a host of dynamic phenomena that stem from the presence and mobility of premelted liquid at subzero temperatures. Accurate assessments of the progressive liquid---ice phase transition is required for predictive models of frost damage, glacier---till coupling, and many other cold regions processes, as well as for evaluating the capacity for water storage in near-surface extraterrestrial environments. We use a Monte Carlo approach to sample the pore space in a synthetic 3D packing of poly-dispersed spherical particles, and evaluate local geometrical constraints that allow us to assess changes in the relative proportions of pore fluid and ice. By approximating the phase boundary geometry in fine-grained pores while considering both the curvature of the liquid---ice interface and wetting interactions with matrix particles, our model predicts changes in phase equilibrium in granular media over a broad temperature range, where present accounting for the colligative effects of chloride and perchlorate solutes. In addition to formulating the constitutive behavior needed to better understand properties and processes in frozen soils, our results also provide insight into other aspects of phase equilibria in porous media, including the formation of methane hydrates in permafrost and marine sediments, and the partitioning between liquid water and vapor in the vadose zone.