Monitoring gas hydrates under multiphase flow in a high pressure flow loop by means of an acoustic emission technology

Abstract

The formation of natural gas hydrates in oil and gas pipelines is an important concern due to the risk of hydrate blockage. In order to reduce the expenses with the use of chemicals to avoid hydrate plugging, more studies about the slurry flow and the mechanisms of blockage in flowing conditions are necessary. In this study, it is presented an experimental work combined with a multi-instrumental data analysis to allow monitoring hydrate formation and track the particles in time and space. Acoustic emission (AE) is used in a high pressure flow loop apparatus to capture acoustic waves generated by the flow and to detect the presence of hydrates flowing in the system. The tests are conducted with Kerdane oil, saline water and natural gas at 75 bar and 4 °C. Two tests are presented, one at 30 and another at 80% water cut (water fraction in volume). It is shown that, with the absolute energy obtained from the AE sensors, it was possible to detect the beginning of hydrate crystallization and the hydrates displacement in the pipeline, because the absolute energy increases as the collisions of particles generate more acoustic emission. The results show that, for the tests performed, the flow became heterogeneous after hydrate formation, with some regions of the flowing volume containing more hydrates than others. It is also shown that the non-flowing volume of hydrates with entrapped liquid, caused by deposition or settling, can be estimated with AE.