Study Correlates Hydrate Blockage Risk and Gas/Liquid Flow Pattern In Horizontal Pipelines

Abstract

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper Paper SPE 197534, “Study on the Correlation Between Hydrate Formation-Blockage Risk and Gas/Liquid Flow Pattern in Horizontal Pipelines,” by Wenyuan Liu, Jinqiu Hu, and Fengrui Sun, China University of Petroleum-Beijing, et al., prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 9–12 November. The paper has not been peer reviewed. Current research into the risk of hydrate formation and blockage in pipelines is limited to prediction of hydrate formation. However, hydrate generation often does not lead to flow barriers. Hydrate growth and deposition rates are important to hydrate generation as a blockage risk. To help solve the problem of flow assurance in horizontal gas/liquid pipelines, this paper analyzes the risk of hydrate formation and blockage, aiming at various gas/liquid flow patterns and considering the phase distribution and interface distribution characteristics of different flow patterns. Introduction Hydrate blockage risk in transportation pipelines is one of the most important topics in the study of flow assurance. Large-scale natural gas development, for example, requires construction of large-scale gathering and transmission pipeline networks. Natural gas is often transported by horizontal or small inclined pipelines, and water generation and flow are often present in natural gas pipelines, which undoubtedly increases the risk of hydrate formation and blockage. When gas and water exist at the same time, there will often be a variety of gas/liquid flow patterns in pipelines, and different flow patterns will have different risk of hydrate formation and blockage. To avoid hydrate risk, it is necessary to study the correlation between hydrate generation blockage risk and gas/liquid flow pattern. Research of Hydrate Growth and Deposition Based on the hydrate formation-growth-deposition mechanism and combined with the hydrate experiment in the flow loop, the characteristics of hydrate formation-growth-deposition in pipe-lines under different gas/liquid flow patterns was studied. The results show that different flow patterns yield different hydrate formation and deposition characteristics as a result of different phase and interface distributions. The bubble flow, cluster flow, and slug flow have some similarities in flow patterns. 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. Thus, the hydrate formation and deposition risk of the latter three flow patterns is significantly greater than that of the former three. Comprehensive analysis shows that the hydrate risk of each flow pattern is in the order of, with greatest risk first, 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. In this case, special attention should be paid to hydrate prevention and control. The complete paper presents a detailed historical discussion of correct division of flow pattern and of research on hydrate growth models. Researchers have established a series of hydrate-growth kinetics models combined with crystallography, heat transfer, mass transfer, and other principles. Recent models established a hydrate growth model based on heat transfer.