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8732789 
Meetings & Symposia 
A practical model to estimate the pore-fracture deformation in dry/wet rocks and in enhanced geothermal systems 
Arriaga, MCS; Verduzco, FS 
2003 
27 
733-736 
English 
The world literature on rock mechanics describes the existence of subsidence in aquifers, in petroleum and gas fields, and in geothermal reservoirs. All these natural systems could be fractured or not. The phenomenon is a direct consequence of the deformation of the poro-elastic media. The fluid extraction causes the reduction of both the internal pore-fracture pressure and of the effective aperture of pores and fractures. On the other hand, the cohesive structure of rocks is weakened by the presence of liquid in the pores. As a consequence all the rock geomechanical parameters are influenced by that cohesion and are directly affected by the pressure and amount of liquid present in pores and fractures. Many naturally fractured systems had intense tectonic activity in their remote past and their original fracturing was equally intense. But some of them could contain fissured zones where most of the fractures appear closed. This phenomenon is partially explained by the fact that dry rock deformation and saturated rock deformation are very different. The first one can be anelastic or plastic, while the second one could be totally elastic. For example, if at the geological moment of being formed a volcanic reservoir was unable to store more than sufficient water, the lack of fluid could produce the collapse of fractures and faults, originating a low or zero global permeability with strong pressure gradients between the matrix blocks and the few open fissures. This effect can be accentuated by autosealing during the water-rock interaction. In that case the chemical equilibrium between water and rock cannot be attained. In this paper we present the development of a simple, practical poroelastic model to estimate, with few data, the deformation of fractured porous rock in dry or wet geothermal systems. These results can be useful in the study of enhanced hydrothermal reservoirs. 
Collapse of fractures; Enhanced geothermal systems; Hot dry rock; Low permeability; Low porosity; Porous rock deformation; Subsidence; Volcanic reservoirs