Gas hydrate behaviour under the influence of Sow dosage hydrate inhibitors (LDHIs)

摘要

Gas hydrate behaviour under the influence of low dosage hydrate inhibitors (LDHIs) has been examined in high-pressure gas/water experiments. Today, the oil companies are focusing on the positive experience by using LDHIs. LDHIs can be added to the fluid systems in much smaller amounts than thermodynamic inhibitors (TIs). This quality saves transport costs, space at offshore installations, causes minor pressure drop, and thereby decreases the need for extra pump capacity. However, little research has been done about how these inhibitors actually influence gas hydrate behaviour. The influence of a kinetic inhibitor (KI) and a commercial anti-agglomerant inhibitor (AA) was evaluated in a structure II forming gas/water system. Several parameters were observed, measured and calculated during a 4-month study. Special care was given to pressure build-up as a function of increasing temperature during dissociation. Significant changes in induction time, crystal growth, gas consumption, morphology, hydrate formation and dissociation pattern were observed. The presence of AA in the fluid system increased the hydrate induction time, but did not affect the further crystal growth. A critical change in induction time was observed between a concentration of 1 wt% and 5 wt% AA. The dissociation time increased by a factor of 7 when KI was presented in the system and by a factor of 3 when AA was added. The efficiency of the KI was dependent on concentration, and the dissociation pattern indicated kinetic behaviour. The dissociation pattern for the AA system was different, and the increased dissociation time may be a result of reduced heat transfer due to high porosity in the hydrate. This paper presents the laboratory work, the experimental results, a comparative study with other available experience, and discusses the potential for implementation in further research and practical handling of such fluid systems offshore.