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.