Investigating fracture network creation and stimulation mechanism of EGS reservoirs. (January 2023)

• Record Type: Journal Article
• Authors: Abe, Ayaka; Horne, Roland N.
• Is Part Of: Geothermics. Volume 107(2023)
• Publication Date: 2023-01
• Subjects: Enhanced geothermal systems -- Hydraulic stimulation -- Mixed-mechanism stimulation -- Wing cracks -- Numerical modeling; Hydrogeology -- Periodicals; Geothermal resources -- Periodicals; Énergie géothermique -- Périodiques; GEOTHERMAL ENGINEERING; GEOTHERMAL ENERGY; GEOTHERMAL EXPLORATION; Geothermal resources; Hydrogeology; Periodicals; Electronic journals; 621.44
• DOI: 10.1016/j.geothermics.2022.102606
• Languages: English
• ISSNs: 0375-6505

Abstract

Highlights: Stimulation mechanisms at two actual EGS projects were investigated by a physics-based numerical model. Resulting fracture networks at two EGS projects showed different features: The network created in the Fenton Hill setting showed a broad shape with more flow paths branching while the network created in the Basel setting showed a narrow shape with rather straight flow paths. The orientation of dominant preexisting natural fractures and the state of stress may have an impact on the overall fracture network geometry One of the implications of this study is that stimulating a reservoir with preexisting fractures with dominant orientation close to the orientation of the maximum horizontal stress may make a complex and broad shaped fracture network, which is more suitable for EGS. 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 and dominant orientation of preexisting fractures and their initial connectivity. This study implies that stimulating a reservoir with poorly-oriented preexisting fractures may result a complex and broad shaped fracture network, which is beneficial for energy recovery.