Evolution of fracture permeability with respect to fluid/rock interactions under thermohydromechanical conditions: development of experimental reactive percolation tests

Abstract : The evolution of fracture permeability is crucial as regards the lifespan of the deep fractured geothermal exchanger of an Enhanced Geothermal System (EGS) site. The objective in developing reactive percolation tests in fractures under ThermoHydroMechanical (THM) conditions is to improve our understanding of fluid/rock interactions and their role in the evolution of fracture permeability. This article describes the test apparatus and the experimental protocol developed to meet this objective. The data from a test on a sample of fractured granite are interpreted with a view to characterising the phenomena that occurred during the reactive percolation and their impact on the behaviour of the fracture and its permeability. The test showed that the free face type dissolution of some minerals led, through a deepening of existing channels on the fracture walls, to an increase of the fracture’s permeability by one order of magnitude and to a change in its hydromechanical behaviour.