Molecular Dynamics Simulation of the Crystal Nucleation and Growth Behavior of Methane Hydrate in the Presence of the Surface and Nanopores of Porous Sediment

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Abstract
The hydrate formation behavior in porous sediment has been widely studied because of the importance to the reservoirs and the drilling of natural gas hydrate. However, it is difficult to understand the nucleation and growth mechanism of hydrate in the porous media surface and nanopore by the experimental and numerical simulation method. In the work, a molecular dynamics simulation on the nucleation and growth of CH4 hydrate in the presence of the clay surface and nanopore is carried out. The molecular configurations and microstructure properties are analyzed with the systems containing 1 H2O layer hydrate (System A), 3 H2O layer hydrate (System B) and 6 H2O layer hydrate (System C) in the clay and the bulk solution. It is found that the formation of hydrate is more complex in the porous media than in the pure bulk solution. The cooperativity between hydrate growth and molecular diffusion is involved in the clay nanopore. The hydroxylated edge sites of the clay surface could serve as a source of CH4 molecules to facilitate the hydrate nucleation. The diffusion velocity of molecules is influenced by the growth of the block hydrate in the throats of the clay nanopore. Compared with the hydrate growth in the different pore sizes in the clay, it is found that the pore sizes play an important role in the hydrate growth and molecular diffusion in the clay. This simulation study provide the microscopic mechanism of hydrate nucleation and growth processes in the porous media, which can be favorable for investigation into the formation of natural gas hydrate in sediments.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2015DFA61790)
  • National Natural Science Foundation of China (51225603, 51276182, 51376184)
  • Science and Technology Program of Guangzhou (y307j21001)

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