Gas Hydrate Crystallization in Thin Glass Capillaries: Roles of Supercooling and Wettability

Abstract

We designed and implemented an experimental methodology to investigate gas hydrate formation and growth around a water−guest meniscus in a thin glass capillary, thus mimicking pore-scale processes in sediments. The glass capillary acts as a high-pressure optical cell in a range of supercooling conditions from 0.1 °C, i.e., very close to hydrate dissociation conditions, to ∼35 °C, very near the metastability limit. Liquid or gaseous CO 2 is the guest phase in most of the experiments reported in this paper, and N 2 in a few of them. The setup affords detailed microscopic observation of the roles of the key parameters on hydrate growth and interaction with the substrate: supercooling and substrate wettability. At low supercooling (less than 0.5 °C), a novel hydrate growth process is discovered, which consists of a hollow crystal originating from the meniscus and advancing on the guest side along the glass, fed by a thick water layer sandwiched between the glass and this crystal.

Small But Powerful Optically: Glass Microcapillaries for Studying Complex Fluids or Biological Systems with Submicrolitre Samples under Harsh Conditions

“…Note that an appropriate choice of capillary dimensions is required: it would not have been possible to obtain these results with a glass capillary with dimensions 300µm/400µm (Figure 5). Similar features have recently been observed with CO2 and N2 hydrates [14].…”

Crustal fingering facilitates free-gas methane migration through the hydrate stability zone

“…The location of the thinnest crust corresponds to weaker tensile strength and, thus, is more prone to rupture. Due to the subcooling effect on hydrate growth rate (33), crust that forms later in the experiment grows more slowly and, thus, appears thinner (SI Appendix, Fig. S3).…”

“…These effects modify the pressure (P ) and temperature (T ) at the triple point, allowing for more common occurrence of the three-phase coexistence. Others argue that the three-phase coexistence is, in fact, a thermodynamic nonequilibrium sustained by high rates of gas flux and slow kinetics of hydrate formation, as supported by field-scale observations (5,(25)(26)(27) and, more recently, by laboratory experiments at the core scale (28)(29)(30) and pore scale (31)(32)(33), as well as multiphase flow modeling (34)(35)(36). Despite much effort in understanding the problem from a thermodynamic perspective, few have addressed the fluid-mechanics puzzle of how the formation of solid hydrate, instead of clogging gas-migration pathways, can facilitate free gas flow in porous media.…”

Combining Optical Microscopy and X-ray Computed Tomography Reveals Novel Morphologies and Growth Processes of Methane Hydrate in Sand Pores

“…Up to now, macrophotography and optical microscopy have been mainly used to observe gas hydrates growing at simple interfaces, like those of water drops on a flat substrate under the guest phase or guest-containing phase (e.g., a guest-saturated organic solvent [33][34][35][36][37][38][39][40]), or around a meniscus between the phases in capillaries or larger vessels [41][42][43][44][45]. As a rule, the hydrate forms a crust over the interface between the aqueous and the guest (or guest-containing) phase, often nucleated at the contact line with the substrate or sample cell [46,47].…”