Pore-scale experimental investigation of the fluid flow effects on methane hydrate formation

Methane hydrates (MHs) formation involves the crystallization process of a hybrid system between methane and water. Former studies focus more on macroscopic but lack of visualization and temporal resolution, therefore, microfluidic device was used in this paper. Similar to the icing process, with the influence of supercooling effect, the hybrid system can be easily trapped in a metastable state. Under this circumstance, crystallization between methane and water molecules will not easily appear spontaneously, significantly extending the induction time. Therefore, artificial approaches are needed during the hydrate formation processes. In this work, based on microfluidic chips, a high-pressure visible device was designed and 2 kinds of perturbation methods were employed during the experiments. Both methods caused disturbance to the hybrid system, breaking the metastable state and achieving hydrate formation inside the microfluidic chips of the different pore structures. The results showed that hydrate formation in microfluidic chips require phase equilibrium state and perturbation in the regions with crystal nuclei. Perturbation was needed in hydrate formation under microfluidic chips and disturbance caused by constant pressure flow in the random pore structure is the most effective method. The repeated movement of methane-water phase played a significant role in the hydrate reformation process. Due to the heat conduction of hydrate formation and dissociation, the movements of the methane phase, water phase, and hydrate phase repeatedly appeared in the pore structure, and this behavior inside the pores directly caused hydrate reformation.