Gas Hydrate Formation in Water-in-Crude Oil Emulsions: The Role of NaCl in Slurry Stability and Transportability

Abstract

Gas hydrates are solid compounds that can be formed during oil and gas production, causing interruptions in the flow of the produced fluids. Certain crude oil antiagglomerants promote the formation of stable hydrate slurries that do not block the production lines. In these cases, if hydrates are formed, they do not agglomerate, and the resulting slurry is flowable. As produced water composition may influence the stability and characteristics of water/oil emulsions, assessing the impact of water composition on the antiagglomerant properties of crude oils becomes crucial. This study aimed to evaluate the influence of brines containing 10 and 20 wt % of NaCl in the presence of three different crude oils on hydrate slurry formation and their flowability. Water-incrude oil emulsions with 40% water cut were prepared for a high-pressure rheometer study. To visualize the hydrate formation process, emulsions with 30% WC were studied by using a rock-flow cell. The key findings revealed that under the same pressure and temperature conditions, with different subcooling, the apparent viscosity of slurries decreased as salinity increased. The differences in the apparent viscosity of the hydrate slurry were minimized for experiments at the same subcooling. The results suggest that the composition of the crude oil, subcooling levels, and morphology of hydrate particles may explain the effects of NaCl and possibly other salts on the agglomeration process of hydrates when crude oil phases are present. The practical implications of these findings relate directly to the management of hydrate-related risks during transient operations in offshore oil production.