Hongyan Ji

Gas Hydrates in Oil Systems

Extensive studies have been conducted on hydrate formation in gaseous systems; however, little information is available on hydrate risks in oil systems. This is partly due to difficulties in measuring the hydrate stability zone in oil systems, as well as problems associated with compositional representation of such systems. Furthermore, it is reported that hydrate formation pose less risks in oil systems than gas systems, partly due to the presence of natural inhibitors, formation of water in oil emulsions, and possibly oil wet pipeline walls. However, little is known of the nature and mechanism of the natural inhibition and the response of the system to an increase in the water cut. In this communication, we present details of two experimental set-ups specifically designed to study the hydrate risks in oil systems. They include a visual high pressure kinetic rig for measuring the hydrate stability zone, crystal size, distribution and the rate of hydrate formation and dissociation, and a glass micromodel for visual observation of hydrate formation / dissociation in micro-scale. We report some of the recently obtained experimental results using the above experimental equipment. The results show that the existing techniques should be revisited for generating reliable data in oil system. We also demonstrate that proper characterization of the heavy end and taking into account the possibility of wax formation may play a role in improving the reliability of predictive techniques. The results provide better understanding and evaluation of risks associated with hydrate formation in pipelines carrying oil.