Experimental characterization of hydrate formation in non-emulsifying systems upon shut-in and restart conditions

In offshore oil production, scheduled or emergency shutdowns of the production system may occur due to maintenance, equipment failure, production issues, and weather-related events. During the shut-in, the fluids may enter into the hydrate zone because of the thermal energy transfer to the cold ocean waters, increasing the risk of hydrate formation during the shut-in period and upon the restart of the production system. This work is focused on identifying some parameters that influence the hydrate formation in shut-in and restart conditions. Using a rock-flow cell with visual capabilities, the hydrate formation and the phenomena involved upon the restart were investigated. The main results of the experiments showed that the high shear conditions applied at the restart promoted water dispersion into the oil phase and contributed to the dispersion of hydrates. In addition, the low shear rate favored the formation of hydrate deposits while hydrate agglomerate was formed at high shear rate. Besides the shear rate, the subcooling proved to be an important parameter that favors the hydrate formation under sheared conditions. Conditions with high subcooling and low water cut promoted the formation of small hydrate particles (similar to 2 mm) that can be dispersed in the oil-phase even without the antiagglomerant. A high subcooling promoted the formation of dry hydrates, preventing the particles to stick with each other (agglomerates). The results indicated that subcooling is an important parameter to ensure a safe restart in the pipeline. Lastly, the addition of an anti-agglomerant reduced the water-oil interfacial tension, which promoted the water/hydrate dispersion; the effectiveness of the anti-agglomerant was clearly affected by the shear and the water cut.

Automated summary

This study focused on identifying parameters that influence hydrate formation in shut-in and restart conditions in offshore oil production. Results showed that shear rate and subcooling are key parameters, and the addition of anti-agglomerant reduces water-oil interfacial tension, promoting water/hydrate dispersion.