| Abstract |
The magnitude of induced earthquakes is determined by the pressure and flow rate of the injected water and the subsurface structure during hydraulic fracturing for development of Enhanced Geothermal System (EGS). The relationship between hydraulic fracturing and induced earthquakes needs to be quantified in order to reduce the induced earthquakes. The energy balance of hydraulic fracturing is analyzed by adopting a model of a rectangular rock body that causes induced earthquakes in this paper. The input is the water injection energy Ei, and the outputs are the earthquake energy Es of induced earthquakes, the frictional energy Ef of the slip surface, the energy of water pressure compressing the rock body Ed, and the pressure loss energy Ep of water through the fracture. In addition, the thickness of the rock body was taken as the average value of the natural fracture spacing data, and the ratio of width and length to the thickness, the friction coefficient of the slip surface of the rock body, and the fracture opening height were adopted as parameters. Using hydraulic fracturing data from the Soultz, Cooper Basin, Basel and Pohang sites, the earthquake energy was estimated using the Gutenberg-Lichter magnitude distribution law, and it was shown that the energy balance is approximately valid. The ratio of the earthquake energy Es to the water injection energy Ei is found to be a few percent. However, the ratio of Es+Ef+Ed+Ep to the injection energy Ei varied significantly from 0.1 to 0.9, depending on the value of the parameters. It was found that the optimal values of the parameters needed to be set at different sites. It is useful to clarify the energy balance of hydraulic fracturing for the selection of the power plant construction site and setting of hydraulic fracturing conditions. |