Creating a hierarchy of fracture network in enhanced geothermal systems (EGS) through innovative hydraulic fracturing stimulation (ETH Grant_Ma)
The proposed project seeks to demonstrate that the creation of a hierarchy of fracture network is necessary for an effective stimulation of the deep geothermal reservoirs (i.e., hot dry rocks). We will provide the proof-of-concept in a tailored field experiment that the fracture hierarchy is best achieved by innovative hydraulic fracturing (creating main ‘arteries’) along with the associated hydraulic shearing (developing numerous ‘veins’), enabling the desired fracture surface area for fluid flow and heat conduction in such engineered geothermal systems (EGS). The experiment will be conducted in a well-characterized granite rock mass in the Central Swiss Alps, simulating the geologic condition where hot dry rocks are typically hosted. We will detail how the imposed hydraulic fractures (‘arteries’) fundamentally transform the pre-existing fracture network (‘veins’) into the optimized EGS, representing a significant step towards economic, sustainable and efficient extraction of deep geothermal energy.
This project is in line with the field efforts of ETH Zürich and Swiss Competence Center for Energy Research (SCCER-SoE) on the Bedretto Underground Laboratory (BUL) initiative, which aims to provide an underground facility for multi-disciplinary collaboration. Specifically, our project strives to tackle the following technical challenges:
- Can through-going hydraulic fractures be superimposed on the pre-existing fracture network to form a distinctive fracture hierarchy in crystalline rock masses? (field characterization)
- How to optimize the hydraulic stimulation to effectively combine hydraulic fracturing and shearing so that the degree of fracture hierarchy can be maximized? (field demonstration)
- How to effectively evaluate the created fracture hierarchy according to the desired EGS reservoir characteristics (fracture surface area and connectivity, heat conduction distance, fluid convection distance)? (data analysis)
These challenges will be tackled with through an integrated geomechanics study with multi-disciplinary approaches. Specifically, the study will begin with a field characterization of the pre-existing fracture network, rock mass properties, and the prevailing in situ stress state in the BUL. This will inform whether hydraulic fracturing is feasible to generate such fracture hierarchy and facilitate the customized hydraulic stimulation design. The field experiment will then proceed in line with the field efforts of the BUL activities. The field ‘proof-of-concept’ is evaluated by detailed analysis of in situ performance in relation to the degree of fracture hierarchy and the efficiency of EGS reservoir. The tailored stimulation design and evaluation to EGS requirements have not been attempted before, representing a new paradigm of EGS development.
Project Leader Institution
ETH Zurich
Project Contact
Funding
ETH Research Grant