Rheological Characterization and Formation Protocol of Tetrahydrofuran Hydrate Slurries

The oil industry's main flow assurance problem is the formation of gas hydrates in environmental conditions of high pressure and low temperature. Researches commonly use different materials to mimic gas hydrates in ambient pressure and moderate temperatures. One of these materials is tetrahydrofuran (THF) which forms hydrate slurries at ambient pressure and temperature between 1 and 4 degrees C. The rheology of hydrates determines the conditions associated with the restart of flow after a possible blockage and how this flow will evolve. To understand this kind of material's theology, we developed a hydrate formation protocol that was shown to provide repeatable behavior. After verifying that manual disturbance can lead to higher variance in the resulting outcomes, we employed a thermal shock with a subcooling of 14 degrees C to trigger hydrate formation. We produced final materials associated with three massic concentrations of THF, namely, c = 30%, c = 35%, and c = 40%. As a complementary view concerning the current procedure employed in the literature, we also characterized the material in its solid-like regime by plotting stress curves versus strain and measuring the material's shear modulus. We were not able to obtain material behavior in the liquid-like regime for the lower concentrations, c = 30% and c = 35%. On the other hand, for the concentration of c = 40%, we provided theological material functions for the solid-like and the liquid-like regimes. We characterized aging effects and found that the material behaves reversibly when a convenient resting time is provided. After a subsequent resting time where aging has stopped, the effect of the shear rate level at hydrate formation revealed a non-monotonic behavior in the resulting yield stress. On the basis of its fractal character, this behavior is possibly associated with the strong-link-weak-link theoretical framework developed for waxy oils. Our results differ from what is found in the literature. On the basis of some studies, we believe that this discrepancy is related to the different protocols adopted to form the hydrate slurry.

Automated summary

The main flow assurance problem in the oil industry is the formation of gas hydrates in high pressure and low temperature conditions. Tetrahydrofuran (THF) is commonly used to mimic gas hydrates. This study investigates the rheological properties and behavior of THF, finding different outcomes for different mass concentrations and differing from previous literature.