Methane hydrate were synthesized in fine quartz sand with different size (160～200 mesh, 200～300 mesh, 300～400 mesh, 400～600 mesh) to determine the stable temperature-pressure conditions (p-T) for methane hydrates using step-heating decomposition method. The results showed that fine particles of quartz sand significantly affect methane hydrate stable conditions, of which 160～200 mesh quartz sand is the boundary mesh one whether the p-T conditions for methane hydrate is different or not under experimental tests. The maximum temperature difference for stable conditions of methane hydrates is 1.5 K between fine quartz sand and bulk water. For each of fine particles of quartz sand, the p-T data of methane hydrates is discrete at different temperature and pressure, and p-T data curves intersected in different quartz sand. This is different with the results in the literatures simulated with silica gel or glass bead. In the literatures, the p-T data curve shifts to the left at the same extent.

Key words: quartz sand, methane hydrate, stable condition, formation and dissociation, step-heating dissociation method