Study of the Influence of Temperature and on the Fracture Energy on Synthetic Rocks and Low Permeability Rocks Present in a Geothermal Reservoir

An Enhanced Geothermal System (EGS) is an underground heat exchanger designed to extract thermal energy stored in the hot rock by circulating a relatively cool fluid. The performance of an “EGS” can be improved by creating sets of fractures by injecting high-pressurized water. To understand the hydraulic fracture in an “EGS”, it is important to know the amount of energy needed to create a unit surface of fracture, also called, fracture energy. However, the dependence of temperature has not been well characterized by rocks typical of geothermal systems. Therefore, the objective of this research project is focused on estimating fracture energy of synthetic (low permeable mortars) and natural rock samples for temperatures corresponding to the temperature of such underground rock systems with a new method. The work concentrated in the Mechanical and Hydro-mechanical characterization of synthetic rocks (mortar sample) and rocks to determine its properties: Young modulus E, Poisson ratio ʋ, maximum compressive strength σc, tensile strength 𝛔t and it's coefficient of permeability к. Then, fracture energy was obtained for each rock at different temperatures from an energy balance during the hydraulic fracture test. The parameters obtained reveal an increase in permeability and fracture energy with the increase in temperature in the tests with synthetic rocks and rocks, also the results obtained from the proposed method exhibit a relatively small dispersion. In Synthetic rocks at high temperature (100º C ) a total of 129 J/m2 was necessary. For rocks (limestone) the same trend was observed: at high temperature, the average energy of 218.66 Joules/m2 was measured and at room temperature, it was 184.54 J/m2.