Investigation on Flow Characteristic of NGS through an Annulus

Abstract

In the transportation of natural gas hydrate slurry, problems such as blockage and sedimentation caused by hydrates aggregation are often encountered. In addition, the risk control of hydrate decomposition is particularly important. Therefore, in order to investigate the flow characteristics and morphology of hydrate slurring, the phase equilibrium model of natural gas hydrate in water-based drilling fluid system is established. It is found that substances such as sodium chloride, potassium chloride, and glycerol all cause a decrease in the temperature at which hydrates are formed. Then, the temperature and pressure distribution in annulus tube are calculated based on the mixed flow model. The results show that the NGS through an annulus could be decomposed under most conditions involved in this paper. The higher the volume concentration of the NGS, the lower the temperature in annulus tube. Because the greater the hydrate concentration, the more hydration decomposition along the process, and the decomposition of the hydrate is endothermic, so the decomposition of the hydrate will make the temperature in annulus tube lower. Under the condition that the hydrate concentration is 10% and the inlet flow rate of the drilling fluid is 160 L/s, the inlet temperature of the drilling fluid has a great influence on the temperature in the ring air pipe. When the inlet temperature is relatively low, it is in the stable state of hydrate at the bottom of well and above part of the area. Therefore, controlling the temperature of drilling fluid entry would be a better measure to control the amount of hydrate decomposition.