.jpg)
Speaker
Description
Cold seeps under seafloor manifests the migration of methane-rich fluid from the sedimentary subsurface to the seabed and into the water column, and even reach the atmosphere. As an important way of methane cycling on the Earth, the cold seeps are often accompanied by the occurrence of methane hydrates, which are hydrocarbons resources with the high hydrogen to carbon ratio. However, the interaction influencing mechanism between methane hydrate phase transition and methane-rich fluid (particularly methane gas) seepage in deformable subsurface marine sediments are still lacking knowledge. In this work, we conducted in-situ hydrate formation and dissociation experiments in fine grained clayey sediments collected from the active cold seep area in South China Sea. By advanced X-ray Computed Tomography technology and in-situ heating as well as hydrate phase transition controlling method, we successfully acquired the dynamic hydrate phase transition behaviors and its effects on sediment pore structure evolution, anisotropy methane seepage, and solid migration under complex thermo-hydro-mechanical conditions. It is revealed that methane hydrates first occupy initial sediment pores while generating new pores and fractures in clayey sediments. The filling and generation of pores by hydrate formation and growth lead to the pore morphology evolution. However, we found that the degree of anisotropy decreases while the fractural dimension increases with the growth of hydrate in pores. Meanwhile, hydrate formation results in solid (e.g. sediments and shells) migration, thereby leading to the pore structure transformation. The shape factor of pores increases with hydrate formation and decreases with hydrate dissociation. During hydrate dissociation, we found that hydrate tend to be reformed in clayey sediments before initiating dissociation. The combining effects of hydrates reformation and hydrate dissociation lead to more enlarged pores in sediments. More significantly, the enlarged pores result in unpredictable damage to the sediment structure after the termination of hydrate dissociation. To address this potential poromechanical problem, we further simulate the solid migration process in clayey sediments during the overall hydrate phase transition process. It is found that the solid particles migrate toward the bottom of the sediments during hydrate formation process, leading to the compaction of sediment structure. On the contrary, during hydrate dissociation, the solid particles significantly move toward the upper region of the sediment, as the results of gas and water seepage through the newly generated and enlarged pores. These experimental observations would improve our understanding of the poromechanical controls and influencing mechanisms between hydrate phase transition, pore structure evolution, and hydrocarbon fluid flow in cold seep systems.
| Country | China |
|---|---|
| Conference Proceedings | I am interested in having my paper published in the proceedings. |
| Acceptance of the Terms & Conditions | Click here to agree |
