Investigation of Kinetic Hydrate Inhibitor performance and the mechanism of inhibition

A number of light hydrocarbons are known to form hydrates with water at a combination of low temperature and high pressure. Under these conditions, it is not uncommon for hydrates to form and plug oil and gas pipelines and other equipment, resulting in shutdown, potential risk of explosion, and accidental release of hydrocarbons into the environment. Conventional chemical inhibitors such as methanol and ethylene glycol are the most frequently used tool in hydrate prevention strategies, however, they can result in significant capital and operational costs as well as health, safety and environmental concerns. An alternative to conventional inhibitors are Low Dosage Hydrate Inhibitors (LDHI), of which Kinetic Hydrate Inhibitors (KHIs) are the more frequently used. KHIs are water soluble polymers, which prevent or delay hydrates nucleation and/or growth. Over the last two decades, much has been learnt about the mechanism of KHI; however, gaps still remain in the knowledge surrounding the mechanism of inhibition. The research described in this thesis seeks to increase the understanding of KHI performance and was carried out from 2003 to 2008 and was a part of the Joint Industrial Project (JIP) titled “Micro and Macro-Scale Evaluation of Low Dosage Hydrate Inhibitors” conducted by the Centre for Gas Hydrate Research at Heriot Watt University. The research involved a series of laboratory tests using stirred autoclave reactors that qualitatively demonstrated that the presence of ethanol, methanol and alkanes have a negative impact on the performance of KHI, while salts and synergist 2-Butoxyethanol have a positive impact. The effect of methanol was supplemented with molecular dynamic simulation that demonstrated that the methanol preferentially adheres to the polymer structures. A multi test tube rocking cell was used to generate large volumes of data to investigate the stochastic behaviour of hydrate formation with and without KHI. The results showed that the commencement of hydrate growth is logarithmically related to subcooling, and higher pressures resulted in higher induction at comparative subcooling and driving force. The information gathered improves the understanding of factors that impact the performance of KHI, improves the understanding in the designing of appropriate testing of KHI, and enhances knowledge of kinetics of hydrate nucleation and growth.EPSR