Session: 11-06-01 Production Systems and Subsea Operations

Paper Number: 126094

126094 - Kinetics and Morphology of Gas Hydrate Formation From Monoethylene Glycol Solution Under Under-Inhibited Conditions 

Natural gas hydrate blockage in pipelines is a major challenge for deepwater oil and gas field development. Thermodynamic inhibitors, such as monoethylene glycol (MEG), are widely used to prevent and control hydrate formation. To balance the pipeline operation cost and hydrate blockage risk, thermodynamic under-inhibition has emerged as a novel hydrate management strategy. Under this condition, the effect of MEG on hydrate formation kinetics and mass transfer characteristics at the gas-water interface is a critical issue for deepwater flow assurance.

In this study, in situ high-resolution X-ray CT was used to observe the growth kinetics and morphology of hydrates formed from MEG solution. It was found that MEG changed the growth morphology of xenon hydrate, inhibited the formation of hydrate film at the gas-liquid interface, and induced flocculent growth of hydrate in MEG solution. The concentration of MEG and subcooling were the main factors affecting the hydrate growth morphology. At 2℃ and 0.5MPa, a layer of hydrate film was formed at the gas-liquid interface when the MEG concentration was 0.005 wt%, with the hydrate film hindering the further growth of hydrate. When the MEG concentration increased to 0.02 wt%, the added MEG broke the mass transfer limitation of hydrate film, and hydrate mainly grew on the wall of sample tube, forming a ring of hydrate layer. With the increase of MEG concentration, the hydrate growth rate decreased, and it tended to form flocculent hydrate directly in water solution. Subcooling also affected the hydrate growth morphology, and the higher the subcooling, the faster the hydrate growth rate and the denser the formed hydrate. The gray value of hydrates formed from MEG solution was much lower than that of hydrates particles formed from condensed water droplets, indicating that hydrates blocks formed from MEG solution were not dense hydrates. With the growth of hydrates, the gray value of hydrates gradually increased, suggesting that the saturation or pore filling rate of hydrates crystals increased continuously, and there was less mass transfer resistance of xenon gas in hydrates blocks. During the growth process of hydrates, the surface of hydrates blocks became dense and rough, and there were still low gray value areas inside hydrates blocks, which were speculated to be unconverted water and MEG. Under low concentration conditions (not more than 20wt%) of MEG, dense blocky hydrates were still formed on the surface, which still easily blocked pipelines.

This study investigated the influence mechanism of factors such as MEG concentration, subcooling, etc. on hydrate growth kinetics and mass transfer characteristics under under-inhibition conditions, aiming to expand the safe boundary of oil and gas transportation and provide theoretical guidance for deepwater hydrate flow assurance.

Presenting Author: Huiyong Liang Ningbo Institute of Dalian University of Technology

Presenting Author Biography: Liang Huiyong is a postdoctoral researcher and the technical leader of the oil product testing laboratory at Dalian University of Technology Ningbo Institute. He obtained his PhD degree from Dalian University of Technology. He has been conducting fundamental research on pipeline flow assurance, focusing on natural gas hydrate exploitation, deepwater hydrate blockage monitoring and detection, hydrate formation kinetics, and deepwater pipeline flow safety assurance technology. He has participated in and is currently involved in several national and international projects funded by the National Natural Science Foundation of China. In the past five years, he has published 5 SCI papers as the first author, all of which are TOP journal papers, including 2 papers in Zone 1 of Chinese Academy of Sciences, 2 highly cited papers, and obtained 2 invention patents (including 1 international patent).

Authors:

Huiyong Liang Ningbo Institute of Dalian University of Technology
Xin Lv Ningbo Research Institute of Dalian University of Technology
Jiafei Zhao Dalian University of Technology
Shi Shen Ningbo Research Institute of Dalian University of Technology
Jiawei Chu Ningbo Research Institute of Dalian University of Technology