During the years 1930's, Hammerschmidt showed that the pipelines located in cold areas such as arctic area could be plugged after the gas hydrate crystallization from
light hydrocarbon components and water which is naturally contained into oil.

But, just before the occurrence of a plug, hydrates particles set a problem :

     - The flowing driving force is the differential pressure between the well head and the production facilities area. So the occurrence of gas hydrate phase acts as a
     decrease of this driving force because particles consume the lighter components and decrease the pressure.

     - The viscosity of the fluid increases and so the flow rate decreases which is prejudicial to the productivity of the well.

     - Finally, one has to separated the hydrate phase (solid phase) from the rest of the liquid before it enters in the classical separation apparatus.

The gas hydrate crystallization in pipeline is first appeared in artic area because the temperature is so low that a low pressure is enough to stabilize the hydrate phase.
Such a context occurs in arctic area but in Siberia and south of Argentina too. As the oil exists to the well head, it is at a high temperature corresponding to the
temperature of the sediment in which the well has been drilled. But, as the flow moves along the pipe, its temperature decreases because of the low temperature of
the wall. Finally, the oil is at the same temperature as the surrounding and the gas hydrate crystallization becomes possible. In this situation, the plugging is a problem
but not a catastrophic one because of the relative accessibility of the pipe which makes possible a quick intervention. But one should note that the situation is quite
difficult. Firstly it is not simple to operate on a plug during winter which is the riskier season for plugging. Secondly, the plug separates the pipe into two zones : a high
pressure zone between the head well and the plug and a low pressure zone between the plug and the production facilities area. If the plug and the pipe wall are
suddenly unstuck, ones generates a projectile which can destroy the pipeline at any restriction or facilities apparatus.

The gas hydrate crystallization can occur in subsea pipelines too. The temperature is not low, but the pressure can be very high and sufficient to stabilize the hydrate
phase. This gas hydrate occurrence can be catastrophic there due to the impossibity to access, see and solve the problem. The solution is to decrease the pressure
both on the well head side and on the platform side. But the risk is still to generate a projectile.
 
 

- The first one consists in insulating the pipeline in order to maintain the oil at a constant temperature equal to the temperature at the exit temperature at the well head
which is sufficiently high. The cost is very high but it can be envisaged for the biggest oil pipes which collect the flow of different wells.

- The second solution consists in shifting the equilibrium temperature of gas hydrate in order to make impossible the crystallization. This is possible by injecting
thermodynamical additives which modify the water properties. Such components are alcohols such as glycohols, or salts. But for very deep wells, this solution is not
reasonable because of the quantity of additives to inject, sometimes 50% in mass of the total water flow contained in the oil flow.

- The third solution consists in using dispersants which will allow to transport the hydrate phase without agglomeration and without plugging. But one has to construct
equipment for the separation of the hydrate phase from the rest of the liquid.

- The last solution consist in using a new class of inhibitors called kinetic additives. These components do not affect the thermodynamical properties of water because
they are added in very low quantities, not more than 1% in mass of the total water flow. Their role is to act as crystallization inhibitors by decreasing the rate of
processes such as nucleation, growth and agglomeration. The crystallization becomes so low that it is impossible to observe it during the time range of the transport in
the pipeline.