Investigating stress shadowing effects and fracture propagation patterns: Implications for enhanced geothermal reservoirs

Abstract

During hydraulic stimulation treatment in an enhanced geothermal (EGS) reservoir, it has been suggested that new fractures are initiated from stimulated preexisting fractures and propagate through the reservoir. In this stimulation mechanism, a fracture propagation from a preexisting natural fracture and the interaction of newly formed fractures and preexisting natural fractures play an important role in the creation of a complex fracture network. In this study, we developed a physics-based numerical model that couples fluid flow between fracture surfaces, fracture deformation, and fracture propagation driven by fluid injection to better understand how a fracture network is created by a hydraulic stimulation treatment. The results showed that the created fracture network complexity is affected by the fracture intersection angle, stress state, and injection rates. Having flow path complexity is advantageous in EGS because it increases the heat exchange areas, the fracture surface to rock volume ratio, and the general reservoir permeability. Therefore, the implication from the results of this study to make a better EGS reservoir is to stimulate an EGS reservoir with 1) well-oriented fractures, 2) a high stress ratio, and 3) a low injection rate. These reservoir conditions and stimulation design will likely make more flow paths and create a more complex fracture network.