In this paper we present the initial development of an
operational Tensorial Model to represent the deformation of
porous volcanic rocks. The fundamental equation of the
model is the total flow of mass, solid plus fluid, in a porous
rock which conduces to a natural generalization of Darcy=s
Law for a deformable medium. The total stress tensor is the
sum of the tensor acting on the solid rock plus the tensional
force acting on the fluid. This total stress tensor must satisfy
some classical equilibrium conditions. Assuming that the
geothermal rock is only subjected to small deformations, a
linear Hooke=s Law can be used to represent the
relationship between strains and stresses. In the most general
case an elastic matrix of 49 elements will be obtained in this
way. All its elastic coefficients must be determined
experimentally. Those coefficients could be constants or be
some functions of pressure and temperature. Some practical
assumptions can lead to simplify this general model.
Simplified models could be adapted to well known fluid-energy
flow simulators just by including into its fundamental
equations the Terzaghi=s effect which states that in saturated
rock the effective stresses acting in the pores will be
decreased by the pore-water pressure. These results can be
useful in the study of enhanced hydrothermal reservoirs, in
hot dry rock systems and in the interpretation of
microseismicity data.

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