Hydrate formation and deposition in multiphase flows in pipelines can cause flow barriers and affect normal oil and gas production and transportation operations. Based on the characteristics that hydrates are easily formed in water droplets entrained in the gas phase or on the pipe wall in the gas?dominated system of the horizontal annular flow, a hydrate deposition model of the gas?dominated system with different water contents in the pipe wall was established, and the hydrate deposition rule under different influence factors of horizontal annular flow conditions were analyzed. The results show that the hydrate deposition rate increases with the water content and undercooling increased on the pipe wall in the horizontal annular flow. The deposition rate can increase three times of the original one, and the risk of hydrate blockage increases. Hydrate deposition from condensed water increases with time. This study can provide theoretical reference for subsequent related hydrate blockage and hydrate prevention and control, and has important application value.

The synthesis of gas hydrates with higher saturation under high pressure and low temperature conditions on the seabed was simulated, and use the multi?stage depressurization mode to extract the hydrate as the blank group, and the effects of multi?stage depressurization + alcohol injection, multi?stage depressurization + inorganic salts and chemical agents with different mass concentrations on the decomposition and recovery efficiency of natural gas hydrate were studied. At the same time, according to the experimental results, the chemical agent with the best decomposition efficiency was preferably evaluated. The results show that: the multi?stage depressurization + chemical injection to recover natural gas hydrate can effectively increase the instantaneous gas production rate and improve the overall decomposition efficiency compared with pure depressurization. Among them, the multi?stage depressurization + injection of 30% ethylene glycol has the best performance in alcohols, compared with the pure multi?stage depressurization mode, its decomposition efficiency is increased by 51.3%, and the recovery efficiency within 2 h is increased by 67.3%; the multi?stage depressurization + injection of 15% calcium chloride has the best performance in inorganic salts, compared with the pure multi?stage depressurization mode, its decomposition efficiency is increased by 47.3%, and the recovery efficiency within 2 h is increased by 60.4%. In the actual mining process, the appropriate chemical concentration should be used to avoid environmental pollution.