Fig .6-Flow curves of hydrate slurry under different initial flow rates in pure water system
From the experimental results, no matter from the aspects of hydrate nucleation or plugging mechanism, increasing the flow rate can effectively reduce the risk of plugging. This is also in line with the research conclusions of most scholars(Liu et al. 2021; Zhang et al. 2021; Shi et al. 2018; Zhang et al. 2022). However, although the high shear effect brought by high flow rate and the weakening of cooling effect will limit or inhibit the nucleation growth and aggregation deposition of hydrate under certain conditions, higher flow rate will also provide more nucleation sites, accelerate the interface disturbance and increase the gas-liquid contact area. Accelerating the induction period of hydrates increases the risk of plugging. Therefore, the influence of different initial flow rates under different systems on the flow characteristics of hydrate slurry should be further studied. If the trend of hydrate plugging can be affected by controlling the flow rate, the economic cost of hydrate plugging prevention will be greatly reduced compared with adding chemical additives. Therefore, it is of great practical significance to explore the influence of flow rate on the flow characteristics in the pipeline system for hydrate prevention and control strategy.
3.3 Flow characteristics of hydrate slurry under inclined tube conditions. The actual operation conditions of oil and gas gathering and transportation pipelines are complex. The change of morphology and position of pipeline flow area and the change of pipeline operation conditions will affect the plugging process of hydrate. The flow characteristics of hydrate slurry under various pipeline structures and operation conditions are still unclear. Therefore, the flow and plugging characteristics of hydrate slurry under special conditions of pipeline still need further study. Due to the complexity of natural gas transportation pipeline laying environment and the need of conditions, there are usually parts laid on the slope to form inclined pipelines. The study of hydrate formation and flow characteristics in the slope is of great significance for the prevention of blockage.
In order to further explore the anti-agglomeration performance of the new Anti-agglomerants under the condition of inclined pipe, the plugging time of the system with or without Anti-agglomerants under the conditions of flow rate of 230 L / h, water content of 100 % and pipe inclination of 10° relative to the horizontal plane was experimentally explored. Fig. 7 shows the flow curve of the system under the pure water condition of inclined pipe. The plugging time of hydrate slurry without AA and with 0.5 wt % AA was 18 min and 33 min, respectively. Obviously, under the condition of inclined tube, the polymer inhibitor still has excellent anti-coagulation effect. In addition, compared with Fig. 4, it can be seen that the plugging time of hydrate in inclined pipe system is shorter than that in horizontal pipe system. This may be due to the small flow at the dead angle of the inclined pipe, which is prone to hydrate accumulation, resulting in flow blockage and pressure drop increase. The exfoliated hydrate deposits are also easy to accumulate and deposit at the dead angle, so the blockage risk of inclined pipelines is generally higher than that of straight pipelines.