| Abstract |
In EGS reservoirs developed within basement, fault zones are considered being the structures controlling deep flow at the reservoir scale in low porosity materials like granite or metamorphic rocks. Using a large set of petrophysical properties (porosity, density, permeability, thermal conductivity, heat capacity, Vp,-Vs) measured on cores and on other outcropping samples, a model of fault zone is proposed with induced petrophysical properties. The different parts composing the fault zone are 1) the fault core or gauge zone, 2) the damage zone and 3) the protolith; they are usually heterogeneous and show different physical properties. The damage zone is a potential high permeability channel and could become the main pathway for fluids if secondary minerals seal the fault core. Porosity is the lowest within the protolith, between 0.5 and 1%, but can increase up to 15% in the fault zone. Permeability ranges from 10-20m2 in the fresh granite to, at least, 10-14 m2 in the fault core, and thermal conductivity ranges from 1.5 W.K-1m- 1 to 3.7 W.K-1m-1. Finally, variations in specific surface are set over two orders of magnitude. If the lowest values of petrophysical parameters (porosity, permeability) usually characterize the fresh granite far from fault zones, physical properties could show variations spread over their whole respective ranges within these fault zones. All of these results could be used to define the rule of each part in hydro-mechanical or chemical fluid rock interactions and the behaviour of fault zone during fluid flow. Models of the porosity development and of fluid and heat fluxes are also proposed. |