Macroscale insights into heterogeneous hydrate formation and decomposition behaviors in porous media

Abstract

Hydrocarbon fuels are distributed unevenly in the earth, known as heterogeneity. How to harness the nature of heterogeneity for sustainable development of energy sources is the key issue. Herein, the controllable process of heterogeneous hydrate phase transition is firstly realized at macroscale, and three typical hydrate distribution patterns (dispersed, massive, and layered) with the same hydrate saturation are successfully achieved. Macroscale observations revealed the kinetic of heterogeneous hydrate phase transition governed by water and gas transfer in pores. Specifically, a new sequence of “nucleation-growth-migration” driven by water migration for heterogeneous hydrate formation in porous media is proposed. In contrast, gas transportation capacity and reformation probability determine the heterogeneous hydrate decomposition efficiency. Significantly, the phase transition rates between heterogeneous and homogeneous hydrate differs by 2 to 3 times due to mass migration. These results suggest that the porous sediments with facilitated water migration under strong capillary effect are preferable for heterogeneous distribution of hydrocarbon fuels, providing explanations for the enrichment of methane hydrate in marine coarse-grained sandy sediment. Nevertheless, the distribution heterogeneity could be challenging to efficient and economic gas production, raising the demand for targeted approaches to develop natural gas hydrate with different distribution patterns. More significantly, the enhanced hydrate formation rate in porous media by controllable heterogeneous hydrate formation method offered by this work also indicates the feasibility in hydrocarbon capture, storage and transport via hydrate-based technologies.