Structural stability of methane hydrates in porous medium: Raman spectroscopic study.

Thermal and temporal stability of the methane hydrates (MH) at ambient pressure, synthesised in a spherical silica (solid and hollow, with average diameter of 70 μm) matrix, are investigated by the Raman spectroscopy. Identical Raman spectroscopic spectral features for all the synthesized hydrate samples indicate structural resemblance irrespective of matrix. It is observed that the growth of hydrates in hollow silica matrix is homogeneous, while that with solid grain is highly heterogeneous. Temporal and thermal stability of MH depends on the silica matrix. Appearance of the Raman signatures characteristic of MH, in hollow silica, indicates that the hydrates are stable over several hours (upon preserving at 153 K and 0.1 MPa) and until ∼273 K at 0.1 MPa. However, MH in solid silica matrix is highly unstable under similar P, T conditions and they are readily dissociated within 2 h. The thermal stability of these samples at 0.1 MPa is also significantly lower.