Experimental investigation of hydrate formation, plugging and flow properties using a high-pressure viscometer with helical impeller

Abstract

Slurry transport has become a subject of interest in several industries, including oil and gas. The importance of slurry/solid transport in the oil and gas industry is evident in areas of cuttings transport, sand transport and, lately, hydrates. Hydrate formation, if not properly monitored and controlled, may lead to pipeline blockage. To avoid pipeline blockage and other hydrate formation risks, chemical additives are added to the system. Additives such as anti-agglomerants help improve hydrate transportability by dispersing the formed hydrates into slurries and preventing them from sticking to the pipe wall. This enables transportation of highly concentrated slurries. However, the high hydrate volume fractions (HVF) slurries may exhibit complex rheology. There is therefore a great need to correlate flow properties such as friction factor and viscosity to HVF. Hydrate slurry transport is important whether hydrates are deliberately generated for energy storage purposes or hydrates formed because of the prevailing flow conditions. However, when determining the viscosity of a fluid containing solid particles, the conventional viscometer types such as concentric cylinders and cone and plate are often not suitable. This is because either the narrow gap would not accommodate the particle size or their inability to maintain the particles suspended leading to bed formation. In this work, a high-pressure mixer-type viscometer was used to generate and characterize hydrate slurries. This work aims to generate a significant amount of hydrate slurry characterization data that may be used as basis for better rheometer designs, hydrate slurry flow properties modeling or integration of hydrate transportability into general multiphase modeling. Results showed that intermediate watercuts posed the greatest pipeline plugging risk for all the oils tested. The amount of transportable hydrates increased with oil viscosity. Generally, hydrate slurries generated exhibited shear thinning behavior that increased with increasing hydrate volume fraction. However, the overall rheology of these slurries is a complex function of the oil used, watercut, gas added to the system and hydrate solid fraction. Lowering shear rates for high HVF systems resulted in separation. Results in this work further suggest that hydrate transportation may be possible with minimum risk if anti-agglomerants are used and high enough shear is applied. On the other hand, if no anti-agglomerant is used, severe aggregation may result in flow line plugging.