Abstract:A proper form of the Rayleigh number, containing the geometric mean of the vertical and horizontal permeabilities was obtained. The critical value for the onset of stable convection was found. The results proved analytically and numerically that anisotropy in permeability resists the initiation of hydrothermal convection. The equivalence between homogeneously anisotropic media and multiply fractured media was also investigated. It was confirmed that multiply fractured models are comparable to anisotropic models as long as they have the same averaged horizontal or vertical permeabilities and other physical parameters.

Key words: hydrothermal fluid circulation; anisotropic permeable media; fractures