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[Display omitted] • Raman spectroscopy can record the formation process of methane hydrate from the solution droplet in the presence of KHI. • The hydrate formation process of KHI-containing systems can be divided into four different stages. • Lactam and non-lactam KHIs have different effects on different stages of the hydrate formation process. • The evolutions of water molecules and guest molecules during the hydrate formation process can be affected differently by varying types of KHIs. In-situ microscopic observation on methane hydrate formation in the presence of kinetic hydrate inhibitor, poly (vinyl caprolactam) (PVCap) or poly (N -isopropyl acrylamide) (PNIPAM), is conducted with a confocal Raman imaging microscope, and the behaviors of CH 4 molecules and water molecules in hydrate formation process are studied to understand the inhibition mechanism. It is found that both PVCap and PNIPAM have influences on hydrate formation, but their interactions with host and guest molecules are different. PVCap with cyclic pendant groups works better on preventing hydrate formation from the gas–liquid interface into the bulk solution, while PNIPAM with acyclic pendant groups is more effectively on inhibiting hydrate growth to well-ordered clathrate structures. Those are caused by the difference in the prominent inhibition mechanism of the two types of kinetic hydrate inhibitors, lactam-based PVCap mainly limiting the diffusion of CH 4 molecules from the gaseous phase to the liquid phase, while non-lactam PNIPAM undermining hydrate growth by retarding the rearrangement of water molecules to form clathrate structures. [ABSTRACT FROM AUTHOR]

Experiments are performed to study the closed-loop effect of gas hydrate formation and decomposition on the flow properties of a fine-grained quartz sand specimen. The high resolution X-ray CT images of the test specimen at different experimental stages are acquired. In order to elucidate the changes in pore structure of the test specimen, topologically representative pore networks are established. The evolution of the flow properties during gas hydrate formation and decomposition is further evaluated. The results show that, gas hydrates occupancy in pore space exhibit different modes; they grow mainly as the grain-cementing mode except some intermediate stages, where pore-filling or load-bearing hydrates are observed. It is also found that the formation and decomposition of gas hydrates can cause the pore structure and flow properties changed. Increase of gas hydrate saturation results in a sharp decline in water relative permeability, larger irreducible water saturation and smaller gas-water percolation zone, while gas relative permeability does not exhibit obvious changing law. The decomposition of gas hydrates will exert a greater influence on the flow properties described above than gas hydrate formation does. The increase in frequency percentage of 10–20 μm pores within the fine-grained test specimen after experiments might be caused by gas hydrate decomposition induced damage of pore structure. [ABSTRACT FROM AUTHOR]