Abstract
Geothermal energy is an important resource to substitute for traditional fossil fuels. The mechanical properties of reservoir rock under the conditions of water and scCO2 injection at different temperatures are crucial for the safety of Enhanced Geothermal Systems. However, the effects of working fluid on the mechanical properties of granite at in situ temperatures are still rarely reported. To reveal the impact mechanisms, conventional triaxial compression experiments were conducted on granite specimens with different confining pressures (2–20 MPa), different pore fluid (10 MPa water or CO2), and different temperatures (25–150°C) in the present study. SEM analyses were applied to the specimens to determine failure surface morphologies after the experiments. The experimental results show that the effective confining pressure, pore fluid, and temperature have significant effects on the strength of granite specimens. The strength of granite increases with the increase of effective confining pressure, with similar granite strength under the same effective confining pressure (dry, water, and CO2). Temperature strengthening of granite is limited by high confining pressure (∼15 MPa). Under the effective confining pressure of 5 MPa, temperature weakening occurs on granite specimens when temperature is higher than 90°C. There is fluid diffusion in the specimens during compression. The higher viscosity of water may cause a temporary decrease in effective confining pressure, which may increase the strength of granite. The growth or formation of cracks is mainly observed in quartz and feldspar grains without short‐term chemical effects. More visible cracks are observed on the specimens and more volume of fluid is injected under CO2 injection conditions, which may be beneficial to increase the permeability of geothermal reservoir.
Highlights
Geothermal energy has been identified as a renewable energy source to substitute for traditional fossil fuels due to its advantages of low carbon emissions, large reserves, and wide distribution [1, 2]. ere are four main kinds of geothermal resources: hot dry rock (HDR), geopressured, hydrothermal, and magma resources, among which HDR is an important available geothermal resource
To illustrate the effects of confining pressure and temperature on the compressive strength of granite specimens, the experimental results are plotted in Figure 3. is figure shows that the rock strength increases with increasing confining pressure
A series of conventional triaxial compression experiments were conducted on granite specimens from Qichun, Hubei Province, China, under different confining pressures (2–20 MPa), different injection fluid (10 MPa water or CO2), and different temperatures (25–150°C). e main conclusions are as follows: (1) e injection of water and CO2 reduces the strength and elastic modulus of granite
Summary
Geothermal energy has been identified as a renewable energy source to substitute for traditional fossil fuels due to its advantages of low carbon emissions, large reserves, and wide distribution [1, 2]. ere are four main kinds of geothermal resources: hot dry rock (HDR), geopressured, hydrothermal, and magma resources, among which HDR is an important available geothermal resource. Ere are four main kinds of geothermal resources: hot dry rock (HDR), geopressured, hydrothermal, and magma resources, among which HDR is an important available geothermal resource. As a notable method of geothermal exploitation, EGS was proposed on the basis of hot dry rock mining technology [3, 4]. The high-temperature and high-pressure geological conditions of geothermal reservoirs are a challenge for geothermal development projects. Under these thermo-hydro-mechano-chemical coupling conditions, the mechanical properties of granite are a basic scientific problem that needs to be studied. Laboratory experiments conducted under geothermal conditions can provide basic predictions for actual EGS projects. Related experimental studies have shown that the mechanical properties of granite are affected by confining pressure, pore pressure, and temperature [5,6,7]. e effect of the stress state on the mechanical behaviors of granite has been studied widely based on different failure criteria [8,9,10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callSimilar Papers
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
