RESUMEN
In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH4/C2H6 hydrate adhesion/cohesion forces under low temperature and high pressure conditions. A CH4/C2H6 gas mixture was used as the hydrate former. Adhesion forces between hydrate particles and carbon steel (CS) surfaces were measured, and the effects of corrosion on adhesion forces were analyzed. The influences of NaCl concentration on the cohesion force between CH4/C2H6 hydrate particles were also studied for gas-dominated systems. It was observed that there was no measurable adhesion force for pristine (no corrosion) and corroded surfaces, when there was no condensed water or water droplet on these surfaces. With water on the surface (the estimated water amount was around 1.7 µg mm-2), a hydrate film growth process was observed during the measurement. CS samples were soaked in NaCl solution to obtain different extents of corrosion on surfaces, and adhesion measurements were performed on both pristine and corroded samples. The adhesion force was found to increase with increasing soak times in 5 wt% NaCl (resulting in more visual corrosion) by up to 500%. For the effect of salinity on cohesion forces, it was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model.
RESUMEN
Investigating the effect of surfactants on clathrate hydrate growth and morphology, especially particle shell strength and cohesion force, is critical to advancing new strategies to mitigate hydrate plug formation. In this study, dodecylbenzenesulfonic acid and polysorbate 80 surfactants were included during the growth of cyclopentane hydrates at several concentrations above and below the critical micelle concentration. A novel micromechanical method was applied to determine the force required to puncture the hydrate shell using a glass cantilever (with and without surfactants), with annealing times ranging from immediately after the hydrate nucleated to 90 minutes after formation. It was shown that the puncture force was decreased by the addition of both surfactants up to a maximum of 79%. Over the entire range of annealing times (0-90 minutes), the thickness of the hydrate shell was also measured. However, there was no clear change in shell thickness with the addition of surfactants. The growth rate of the hydrate shell was found to vary less than 15% with the addition of surfactants. The cohesive force between two hydrate particles was measured for each surfactant and found to be reduced by 28% to 78%. Interfacial tension measurements were also performed. Based on these results, microscopic changes to the hydrate shell morphology (due to the presence of surfactants) were proposed to cause the decrease in the force required to break the hydrate shell, since no macroscopic morphology changes were observed. Understanding the hydrate shell strength can be critical to reducing the capillary bridge interaction between hydrate particles or controlling the release of unconverted water from the interior of the hydrate particle, which can cause rapid hydrate conversion.
RESUMEN
The present work uses a micromechanical force apparatus to directly measure cyclopentane clathrate hydrate cohesive force and hydrate-steel adhesive force, as a function of contact time, contact force and temperature. We present a hydrate interparticle force model, which includes capillary and sintering contributions and is based on fundamental interparticle force theories. In this process, we estimate the cyclopentane hydrate tensile strength to be approximately 0.91 MPa. This hydrate interparticle force model also predicts the effect of temperature on hydrate particle cohesion force. Finally, we present the first direct measurements of hydrate cohesive force in the gas phase to be 9.1 ± 2.1 mN/m at approximately 3 °C (as opposed to 4.3 ± 0.4 mN/m in liquid cyclopentane).