Investigating Fracture Network Creation and Stimulation Mechanism of Egs Reservoirs

Abstract

Based on the observation of past EGS projects, it is suggested that hydraulic stimulation created a complex fracture network including both preexisting fractures and newly formed fractures. To better understand the hydraulic stimulation mechanisms in an actual EGS reservoir, we applied the geological and operational parameters of Fenton Hill Phase-2 reservoir and Basel EGS site to our physics-based numerical model to investigate how a preexisting fracture and a newly formed fracture interact with each other and create a fracture network. The results show that the network created in the Fenton Hill setting showed a broad shape with more flow path branching while the network created in the Basel setting showed a narrow shape with rather straight flow paths. The results of this study suggest that the dimension, migrating orientation, and complexity of a fracture network are controlled by the state of stress, injection rates, and dominant orientation of preexisting fractures and their initial connectivity. This study implies that stimulating a reservoir with disoriented preexisting fractures may result a complex and broad shaped fracture network, which is beneficial for energy recovery.

Keywords: enhanced geothermal systems, hydraulic stimulation, mixed-mechanism stimulation, stress shadowing, wing cracks, and numerical modeling