Abstract

Hydrate formation and blockage in pipelines are serious problems in the oil-gas production and transportation. The current research is limited to the prediction of pipeline hydrate formation. However, the small hydrate generation often does not form obvious pipeline flow-barriers. Therefore, compared with hydrate formation, hydrate growth rate and deposition rate is equally important for the emergence of flow barriers. Based on the hydrate formation-growth-deposition mechanism and combined with the hydrate experiment in the flowloop, the characteristics of hydrate formation-growth-deposition in pipelines under different gas-liquid flow patterns was studied. The results show: Different flow patterns show different hydrate formation and deposition characteristics due to different phase distribution and interface distribution. The bubble flow, cluster flow and slug flow have some similarities in flow patterns. It can be seen that the gas phase in the flow system exists in the form of bubbles, and the occurrence of thin liquid film on the tube wall under these three flow patterns is relatively rare; accordingly, the similarity of laminar flow, wave flow and annular-mist flow shows that thin liquid film or gas-liquid-pipe wall three-phase interface will always appear in the flow process, which will make the hydrate formation and deposition risk of the latter three flow patterns significantly greater than the former three flow patterns. Comprehensive analysis shows that the hydrate risk of each flow pattern is in the order of annular-mist flow > laminar flow and wave flow > slug flow > cluster flow and bubble flow. The annular-mist flow is the most dangerous flow pattern for hydrate formation and blockage, which is quite common in the oil and gas industry. In this case, special attention should be paid to hydrate prevention and control.

It is hoped that the research in this paper can provide some theoretical guidance for field construction and related researchers.

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