Hydrate plugging mechanisms of oil-dominated, water- dominated and partially dispersed system
2017
It is the hydrate plugging mechanisms of multiphase flow that are
the key to implement hydrate risk management, which have always been
the focus of flow assurance industry. This paper reviews the experiments
and principle analysis conducted by many researchers, and summarizes
types of experimental equipment and methods, and then concludes different
mechanisms for hydrate plugging in oil-dominated system, water-dominated
system and partially dispersed system, while giving out some suggestions
for further researches. Because of the lack of field data and the
difficulty of conducting field plugging experiments, at present, designing
experimental apparatus is the common solution around the world, such
as autoclave and flowloop, to undertake simulation study, with the
purpose to investigate plugging mechanisms. Stirring and rocking are
two main methods for autoclaves to simulate pipe flow, which results
in the flow characters of autoclaves is different from the real pipe
flow. So flowloops are superior to autoclaves in simulating pipe flow,
while some visual autoclaves (sapphire cell and so on) are better
than flowloops in direct visual observation. In micro level, FBRM
and PVM could provide particle distribution and behavior information.
MMF apparatus could measure cohesive force between particles and adhesive
force between particles and pipe walls. These micro level apparatus
would help to estimate the tensile strength and the size of aggregates,
which are meaningful to predict rheological properties of the fluid
and the pressure drop of the pipeline. More efforts should be done
on the combination of micro measurement and macro measurement, and
finding a better way for autoclaves to simulate pipe flow more accurately
and a better way for flowloops to improve visual observation. Plugging
mechanism will be different when it comes to different multiphase
systems. For oil-dominated system, which has been researched for the
longest time and has the most mature theoretical system, agglomeration,
adhesion to pipe walls and bedding are the governing factors of plugging.
When oil-dominated system is treated by AAs, under risk management,
agglomeration will be weaken significantly. Then the plugging mechanism
of this condition would be controlled by bedding and adhesion to pipe
walls. More works should be done on the theoretical modeling of adhesion
to pipe walls and bedding for oil dominated system, and confirm the
contribution of different mechanism to the pressure drop. For water-dominated
system, research of which is prospective, bedding of hydrate particles
or hydrate network is the determining reason for plugging. Since the
hydrate growth rate of water-dominated system is relatively low, this
system has the lowest plugging tendency. The molding of hydrate growth
for water-dominated system would be the next step work. Research on
partially dispersed system is carried out with the increasing water
cut in the offshore oil fields, which is now in the experiment exploration
period. Plugging of this system is resulted from film growth of the
free water and agglomeration in the bulk phase, which resulting in
the most severe plugging tendency. The quantification of the free
water for partially dispersed system is fundamental for the continuing
study. Moreover, it is significant to take the impact of flow patterns
on the plugging mechanisms into consideration.
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