Hydrated methane in a solid state. A lattice-like chemical structure in which one molecular group is surrounded by others, such as H2O by CH4. Such crystalline, ice-like clathrate compounds can exist at low temperature and high pressure, as in deep-water areas, where its base often gives rise to a bottom-simulating reflection (BSR); see hydrate reflection. Sometimes found in permafrost areas. Hydrates also tend to clog and block flow lines and pipelines. See Sheriff and Geldart (1995, 128).