Imaging methane hydrates growth dynamics in porous media using synchrotron X‐ray computed microtomography

Abstract

Commercial-scale methane (CH 4 ) extraction from natural hydrate deposits remains a challenge due to, among other factors, a poor understanding of hydrate-host sediment interactions under low-temperature and high-pressure conditions that are conducive to their existence. We report the use of synchrotron X-ray computed microtomography (CMT) to image, for the first time, time-resolved pore-scale methane CH 4 hydrate growth from an aqueous solution containing 5 wt % barium chloride (BaCl 2 ) and pressurized CH 4 hosted in glass beads, all contained in an aluminum cell with an effective volume of 3.5 mL. Multiple two-dimensional (2-D) cross-sectional images show CH 4 hydrates, with 7.5 mm resolution, distributed in patches throughout the system without dependence on distance from the cell walls. The time-resolved three-dimensional (3-D) images, constructed from the 2-D slices, exhibited pore-filling hydrate formation from dissolved CH 4 gas, similar to natural CH 4 hydrates (sI) in the marine environment. Furthermore, the 3-D images show that the aqueous phase was the wetting phase of the glass beads, i.e., the host and the formed hydrate were separated by an aqueous layer. These results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale. Pore-filling CH 4 hydrate growth is likely to result in a reduced bulk modulus, and thus, could affect seafloor stability during the reverse phenomenon, i.e., dissociation of natural hydrate deposits.

Interplay of Subduction Tectonics, Sedimentation, and Carbon Cycling

“…Whether hydrate can occur as discrete cement or interconnected between pores is still not fully resolved, but recent experiments measuring both hydrate saturation ( S h ) and P ‐wave velocity ( V p ) under pressure are consistent with a load‐bearing hydrate model as presented by Konno et al (). Imaging of methane hydrates using synchrotron X‐ray computed microtomography have also shown methane hydrate to form interconnected networks in porous media (Kerkar et al, ; Sahoo et al, ). In the scenario we postulate, the gas‐hydrate permeability seal was breached as Site U1379 uplifted beyond the upper limit of gas hydrate stability, freeing the methane‐rich fluids to migrate upward and initiate carbonate precipitation at the SMT.…”

Methane Hydrate in Confined Spaces: An Alternative Storage System

“…Thus, the resolution is currently only appropriate for bulk systems, and not for nanopores. Similarly, X‐ray computed synchrotron microtomography can be used to monitor time‐resolved MH growth with a 7.5 μm resolution . This method, for instance, has shown that the hydrate formation starts from dissolved CH 4 rather than from the gas interface.…”

“…Moreover, MRI cannot visualize methane hydrate coexist with ice . On the other hand, X‐ray computed tomography (CT) has higher spatial resolution than that of MRI, but it is impossible to distinguish gas hydrate and ice without contrast agents except phase contrast X‐ray CT …”

Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

“…The bulk porosity of A‐graded and B‐graded host sands is controlled between 37% and 38%, and the initial water saturation is about 0.5. For reference, various kinds of solutions used as alternatives to pure water can keep enhancing the phase contrast between hydrate and solution in X‐ray CT images during hydrate formation due to the increasing solute concentration (Chen et al, ; Kerkar et al, ; Lei et al, ; Li et al, ; Ta et al, ).…”