CH4-hydrate formation and solid-phase deposition in salt-sand coexisting flow systems
Hydrate reformation and silt deposition blockage in pipelines are key issues affecting combustible ice mining,and seawater in pipelines has a certain degree of salinity.Therefore,this study used a high-pressure loop to carry out water-silt-NaCl-CH4 system hydrate formation and hydrate-silt deposition experiments.The experiments revealed a four-stage evolution process from hydrate formation to stable solid-phase deposition.The study found that in a saline system containing sand,the induction time of hydrate formation can be significantly extended by 2-3 times compared to that in a pure water system.This extension is particularly notable under conditions of low sand concentration(0.1%(mass))and high flow rate(1600 kg/h),reaching a maximum of 3.3 times.This is because of that the disruption of water molecule cluster structures by NaCl and sand is a crucial mechanism inhibiting hydrate nucleation.Furthermore,NaCl compresses the thickness of the particle's double electric layer,weakening the hydrophilicity of sand particles.This,coupled with nanobubble bridging,prompts the aggregation of solid particles and their adhesion to the pipe wall,accelerating the formation of hydrate-sand deposition layers.The research findings contribute to ensuring the safety and stability of multiphase flow in the exploitation and production system for combustible ice development.