Hydrate-calcite and hydrate-quartz adhesive forces were measured with a micromechanical force apparatus. When compared directly to hydrate-steel adhesive forces for the same bulk fluid, both hydrate-mineral forces are 5–9× larger, with significant dependence on the surface roughness of the mineral. From cohesive force data, hydrate-water and hydrate-hydrocarbon interfacial tension values were estimated, yielding an estimated water wetting angle on cyclopentane hydrate of 25° ± 1°. These values can be applied in a simple, pore-scale relative permeability model to assess how the relative permeability of hydrate-saturated sediment can be affected by pore-fluid interfacial tension.
Gas clathrate hydrates are crystalline inclusion compounds, where molecular cages of water surround light hydrocarbon species (e.g., methane), typically at high pressure and low temperature.1 Hydrates occur naturally in oceanic sediments or sediments under the permafrost, where biogenic (most common) and thermogenic methane gas are trapped in these hydrated sediments. Hydrate deposits represent a significant global energy resource;2 the methane sequestered in natural hydrate may be greater than the sum of identified crude oil, natural gas, and coal assets worldwide.2 As of 2009, inferred or known hydrate deposits were identified on or in the costal regions of every continent.3
The fractions of hydrate, free gas, and water play a significant role in determining the macroscopic sediment properties.4 Common sedimentary descriptors, including porosity, permeability, and capillary head, are critical to the successful modeling of hydrate bearing sediment. Energy production from natural hydrates requires a comprehensive understanding of the hydrate-sediment-fluid system behavior, including mechanistic properties (e.g., relative permeability) and transient behavior (e.g., hydrate growth or dissociation properties near equilibrium conditions). Drawing on hydrate experience in conventional oil and gas production, these macroscopic phenomena may be conceptualized as the product of interfacial and bulk contributions (Figure 1).5 Previous modeling efforts have focused on accurately describing sediment characteristics, 6 while select experimental studies have presented interfacial investigations on natural hydrate systems.