Fines migration and pore clogging induced by single- and two-phase fluid flows in porous media: From the perspectives of particle detachment and particle-level forces

Depressurization of hydrate-bearing sediments (HBS) is inevitably accompanied with sediment transport, not only structural host sediment itself but also fine particles, which can be a significant problem in producing gases from HBS, as demonstrated in recent field-scale hydrate production tests. Particularly, the migration of fine sediment particles can alter the hydro-mechanical properties of sediments, and reduce long-term hydrocarbon productivity by causing local-clogging around wells. However, questions as to under which circumstances and to what extent the fines migration and poreclogging occur remain poorly resolved, particularly in association with two-phase flows. Therefore, this study explored the fines migration induced by fluid flows and the resulting pore-clogging in porous media. One-dimensional channel experiments were carried out with sandy sediments containing nonplastic silty fines to examine effects of fluid velocity and mixed fluid flows on pore-clogging occurrence. In single-phase flows, the flow velocity had a pronounced effect on determining the fines behavior, exhibiting from no or minimal fines detachment, through fines migration with no clogging, and to fines migration accompanying pore-clogging with increasing flow velocity. In two-phase flows with mixed gas-water fluids, the presence of gas-water interfaces clearly promoted pore-clogging because the fines were readily collected at gas-water interfaces, resulting in high particle concentration at the menisci. The particle-level force analysis also corroborates the experimental observations, showing that the drag force primarily determined by the flow velocity plays a significant role in the fines detachment against the particle weight in the single-phase flows. In contrast, the gas-water interfacial tension overwhelms the drag force and the particle weight, and thereby, governs pore-clogging behaviors in mixed fluid flow conditions. The presented results provide insights into pore-scale mechanisms of pore-clogging induced by fines migration, which is associated with gas production in HBS, as mixed fluids flow can accompany fines detachment, fines migration, and pore-clogging near wellbores. (C) 2019 Elsevier Ltd. All rights reserved.