One-Dimensional Study on Hydrate Formation from Migrating Dissolved Gas in Sandy Sediments

Abstract

Upward migration of gas-dissolved pore fluid is an important mechanism for many naturally occurring hydrate reservoirs. However, there is limited understanding in this scenario of hydrate formation in sediments. In this preliminary work, hydrate formation and accumulation from dissolved gas in sandy sediments along the migration direction of brine was investigated using a visual hydrate simulator. Visual observation was employed to capture the morphology of hydrates in pores through three sapphire tubes. Meanwhile, the resistivity evolution of sediments was detected to characterize hydrate distribution in sediments. It was observed that hydrates initially formed as a thin film or dispersed crystals and then became a turbid colloidal solution. With hydrate growth, the colloidal solution converted to massive solid hydrates. Electrical resistivity experienced a three-stage evolution process corresponding to the three observed hydrate morphologies. The results of resistivity analysis also indicated that the bottom–up direction of hydrate growth was consistent with the flow direction of brine, and two hydrate accumulation centers successively appeared in the sediments. Hydrates preferentially formed and accumulated in certain depths of the sediments, resulting in heterogeneous hydrate distribution. Even under low saturation, the occurrence of heterogeneous hydrates led to the sharp reduction of sediment permeability.

Review and Outlook of Visual and Geophysical Detections for the Pore-Scale Morphology of Gas Hydrates

“…In addition, Tian et al 134 compared the numerically fitted and experimentally measured n values to determine the hydrate morphology. Li et al 135 synthesized hydrates by dissolved gas in a 1D visual hydrate simulator. Their measured resistivity (S h < 50%) matches the patchy line (Figure 10) and is consistent with the observed hydrate accumulation in the 1D visual hydrate simulator.…”

Hydrate Formation and Methane Mass Transfer Characteristics in Static Systems of Pure Water and Saline Water with Varied Initial Dissolved Methane Concentrations

“…6,7 Notably, the dissolved methane content in seawater can directly influence the microbial absorption process 8 while also affecting the nucleation and growth characteristics of methane conversion to hydrates. 9 In comparison to other reactions, the methane hydrate con- version process on the deep seabed is both more rapid and more pronounced. Moreover, the formation of methane hydrates can, in turn, alter the dissolution rate and saturation concentration of methane seeping from the seabed, thereby significantly influencing the microbial methane oxidation process.…”

“…Methane released from seafloor seepage undergoes a series of complex transformation reactions during its migration through the seabed sediment layer and the marine water column, including methane dissolution, microbial oxidation, chemical conversion, and the formation of solid-phase hydratesplaying a crucial role in effectively intercepting the substantial emissions of methane from the seafloor into the atmosphere. , Notably, the dissolved methane content in seawater can directly influence the microbial absorption process while also affecting the nucleation and growth characteristics of methane conversion to hydrates . In comparison to other reactions, the methane hydrate conversion process on the deep seabed is both more rapid and more pronounced.…”