Influence of Effective Stress on the Permeability of Fractured Hot Dry Rocks

In hot dry rocks changes in water pressure implies variations in effective stress of the fractured rocks and in their fluid transport characteristics, so the growth of water pressure increases permeability and consequently flow rate and heat production. But stimulation processes can also make permeable, or increase the permeability, of the rocks neighbouring the reservoir giving rise to water losses and increasing the cost of the heat production. It is therefore necessary to select strategies to improve the reservoir permeability during the water production, in order to increase the flow rate and the heat production, without causing an excess of water losses from its boundaries. In the paper are examined: the effect of the most common rocks-fracturing techniques, the different characteristics of fractures generated by hydro-stimulation in sedimentary and high-strength crystalline rocks, the relations between permeability, water loss and effective stress.