The problem of thermal crack growth due to cold-water injection has been an important issue as a means of reservoir permeability enhancement in geothermal reservoirs. In this paper, we present numerical investigation of thermal crack growth in the vicinity of a borehole and a fracture during an injection period. The single and multiple fracture propagation caused by transient cooling are numerically modeled using the 2D boundary element method. First, we show the stress and temperature distributions on and near a single crack in an elastic domain to demonstrate the effect of transient cooling on the thermal stresses in a cooled zone. Then, we increase the number of cracks in the domain and consider interactions from multiple fractures and their propagation direction is investigated. In order to increase the accuracy of stress intensity factor calculation, the special crack tip displacement discontinuity element is implemented at the crack tip. Also, maximum principal stress criterion is used to determine crack growth trajectory. Numerical results indicate that the high thermal stresses due to cold-water injection can lead to initiation and propagation of secondary crack growth perpendicular to the main crack. Furthermore, the faster cooling rate produces longer crack growth of the thermal cracks.

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