Progress In Design And Asessment Of Low Dosage Hydrate Inhibitors

Gas hydrates are crystalline compounds formed as a result of combination of water and gas molecules under suitable temperature and pressure conditions. The formation of gas hydrates in subsea pipelines can result in pipeline blockage and cause serious operational and safety concerns. Gas hydrates are generally prevented by injecting the so-called thermodynamic inhibitors, that is methanol, glycol etc. However, these inhibitors may not be economical at high water cuts, in addition to many environmental and logistical issues. Hence, the industry is introducing a new family of inhibitors, called Low Dosage Hydrate Inhibitors (LDHI). The current LDHIs were found and designed on trial and error basis and have limited applications at high degrees of subcooling and/or high-pressure conditions relevant to deepwater applications. Within the framework of a joint project between Heriot-Watt and Warwick Universities, a new approach based on molecular dynamic simulations has been used in the search and design of new LDHIs. The chemicals are then synthesised and tested under simulated offshore conditions. In this paper after describing the test equipment and procedures, the results of the tests on ten of the newly developed LDHIs in the presence of structure I and structure II hydrate forming hydrocarbon systems are presented and compared with two commercially available kinetic inhibitors. The primary mechanism of hydrate inhibition is investigated by the application of glass micromodel set up in visual observation of hydrate formation and growth in the presence of new LDHI. The test results are very encouraging, as two of the new LDHIs (at 0.5 mass% concentration) produced more than 6 hours induction time at 11°C subcooling. The inhibitor at 1 mass%, was tested in the presence of natural gas. The results demonstrated the success of the methodology, as the LDHI was able to prevent gas hydrate formation for 20 hours at 14°C subcooling, comparable with the results obtained from some of the leading commercial inhibitors.