To mitigate the issues of pipeline narrowing and obstruction in metal tubing caused by natural gas hydrate formation during the extraction of onshore natural gas wells, particularly in cold regions, Changqing Oilfield has proposed an integrated gathering and transportation mode termed “Wellbore Insulation-Wellhead Throttling”. This mode uses metal-reinforced composite insulation pipe as the production tubing for natural gas wells. This study simulates the operational conditions of the Changqing Sulige gas field and employs the Computational Fluid Dynamics (CFD) method to examine the multiphase flow characteristics of hydrates within the insulation pipe of this structure. This analysis aims to provide a theoretical foundation for the widespread adoption and implementation of the integrated gathering and transportation mode. The simulation outcomes reveal that the multiphase flow characteristics of hydrate within a metal-reinforced composite insulation pipe are influenced by several factors, including inlet flow rate, solid-phase and liquid-phase volume fractions, hydrate particle size, among others. Under varying operational conditions, the distribution of solid hydrate particles and the liquid phase is characterized by higher concentrations in the central region and lower concentrations near the wall, whereas the gas phase exhibits lower concentrations in the central region and higher concentrations near the wall. For solid hydrates, an increase in volume fraction from 2% to 4% and 6% results in a significant rise in the hydrate concentration gradient. The unit pressure drop of hydrates is predominantly influenced by the inlet flow rate. In practical production scenarios, a gradual decline in gas well production is likely to reduce the inlet flow rate, thereby elevating the risk of hydrate particle deposition and blockage within this structural composite insulation pipe. The solid volume fraction has the most significant influence on hydrate particle size. When the hydrate particles flow from the inlet to the 1 m section, their particle size increases rapidly and then stabilize. The metal-reinforced composite insulation pipe can effectively optimize the distribution of hydrate particles, inhibit deposition and blockage, meet the safe transportation requirements of hydrates in onshore gas fields, and possess significant practical engineering value.
Xi et al. (Thu,) studied this question.