Investigation on plugging prediction of multiphase flow in natural gas hydrate sediment with different field scales

Abstract

The change in water–gas flowrate ratio is one of the main reasons to induce plugging occurrence in the natural gas hydrate (NGH) exploitation process, which significantly influences gas production efficiency. However, there was still no judgment factor to predict multiphase flow plugging in different field scales. Therefore, two sizes cylindrical reactors (Ф50, Ф15) were used in this study, and the difference in effective sectional velocity of water phase (vew) between the two reactors was about 12 times. The entire hydrate re-formation process was directly observed by magnatic resonance imaging (MRI), and the results proved that hydrate re-formation was the main factor for plugging in water–gas flow process. Moreover, the methane concentration gradient across the water and hydrate decreased with the decreasing water flowrate. Thus, the faster mass transfer process on water-hydrate interface enhanced the amount of hydrate re-formation in the two-phase flow process. After validation, the hydrate re-formation amount increased by 11.75% when the vew was reduced by 0.75 m/s. In other words, the higher water flowrate can effectively prevent the plugging of hydrate sediment under the same gas flowrate. Based on the above, the effective sectional velocity was first used to judge plugging occurrence for different scales hydrate sediment. At a given gas effective sectional velocity of 0.23 m/s, the flow plugging phenomenon did not appear when the effective sectional velocity of the water phase was higher than 3.59 m/s for two different scales of hydrate sediment. The results effectively evaluated the plugging occurrence in hydrate sediment with different scales during the water–gas flow process, and further established a bridge between the laboratory investigation and hydrate actual production test.