Thermal Expansion of Triaxially Stressed Mudstone at Elevated Temperatures up to 400°C

Summary Slope instabilities, including prone-to-fall rock columns, are known to exhibit clear vibrational modes. The resonance frequencies of these modes can be tracked by seismic instrumentation, allowing the rock column's mechanical and structural properties to be monitored, as well as providing precursors of imminent irreversible failures. In previous studies, superficial thermoelastic effects were assumed to drive daily fluctuations in resonance frequencies, but no qualitative or quantitative evidence was provided. The results presented here corroborate this hypothesis and quantify the physical processes involved. We interpreted daily variations of resonance frequencies in the Les Arches study site (Vercors, French Prealps) using a thermo-mechanical finite-element model. Modelled fluctuations of the resonance frequencies over a day closely matched experimental observations, reproducing the daytime frequency increase of around 2%. In addition, our model provides explanation of the various behaviors observed across study sites: the frequency response strongly depends on solar exposure, as well as the timing and intensity of both radiative and convective heat fluxes. We highlight acousto-elastic constants as key parameters of our semi-quantitative model, although they remain poorly constrained here. For future instrumentation, we therefore recommend the deployment of pyranometers on rocky sites to accurately invert these parameters over time, thus allowing rock fracturing to be quantitatively tracked by acousto-elastic monitoring.

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“…The thermal expansion coefficient for the whole rock structure was fixed at 𝛼 = 2,8. 10 "7 𝐾 "% (Feng et al 2020).…”

Section: )mentioning

confidence: 99%

Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems

Guillemot

Baillet

Larose

et al. 2022

Geophysical Journal International

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“…Zhou et al found that the thermal strain rate of shale increases rapidly at 200, 350, and 400 °C directly observed through experimental methods . Similar conclusions had been made on the thermal effects on the mechanical properties of clay, mudstone, and sandstone in many publications. − Otherwise, mineralogy, particularly the ratio of clay and quartz, frequently appears to be an important factor to assess the mechanical properties of sedimentary rocks. , For example, the proportion of brittle minerals of quartz and carbonates has been widely used as a brittleness index to assess the feasibility of hydraulic fracturing. , The chemical compositions and the thermal stability are both fundamental for evaluating the mechanical properties of geomaterials. To date, the hydro-mechanical properties and mineralogy of rocks have been separately investigated in most cases.…”

Section: Introductionmentioning

confidence: 74%

“…38−40 As a large amount of heat energy from the explosion and radioactive waste can cause a high reservoir temperature, the effects of high temperature on shale rocks should be investigated. The elevated temperature has been proven as a significant factor affecting the mechanical properties of rocks according to the published papers, 16,17,33,41 which could largely The TGA results in Figure 3 indicate a big weight loss of shale rocks with elevated temperatures. According to geochemistry, weight loss is caused by the physical/chemical reactions happening during the heating operation.…”

Section: Discussionmentioning

confidence: 97%

“…In addition, the depleted shale reservoir has been also taken as a suitable place for nuclear waste disposal. − As a large amount of heat energy from the explosion and radioactive waste can cause a high reservoir temperature, the effects of high temperature on shale rocks should be investigated. The elevated temperature has been proven as a significant factor affecting the mechanical properties of rocks according to the published papers, ,,, which could largely affect the performance of explosive fracturing and radioactive waste disposal. Therefore, a series of tests have been conducted in this work to quantitatively investigate the evolution of shale properties with temperature.…”

Section: Discussionmentioning

confidence: 99%

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Investigation of the Temperature Dependence of the Chemical–Mechanical Properties of the Wufeng–Longmaxi Shale

Zhai

et al. 2022

ACS Omega

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Shale rocks have been widely investigated to evaluate the productivity of oil/gas. The high temperature generated by the explosive fracturing to stimulate the gas reservoir has a significant impact on the chemical−mechanical properties of shale rocks. Pioneering works have been carried out at temperatures below 500 °C, but little has been done to quantify the correlation between the chemical and mechanical properties of shale at temperatures above 500 °C. Therefore, an experimental study on the effect of temperature on the chemical−mechanical properties of shale rocks is presented in this paper. The temperatures used in our experiments are between 0 and 800 °C. Results indicate that there exist strong chemical reactions leading to a big reduction in the sample's weight and mechanical strength for a temperature over 500 °C. Thermogravimetric analysis data demonstrates that the weight of shale powders has little change below 400 °C and largely decreases after 600 °C. It shows that the chemical reaction rate corresponding to shale compositions varies with temperature. X-ray diffraction and Fourier transform infrared are integrated to quantify the occurrence of contained reactions including the decomposition of kerogen, carbonates, and quartz transition. This can provide a temperature range for all possible reactions. Changes in the compositional information of shale samples have been proven to significantly influence the mechanical properties. A 25% decrease in dynamic Young's modulus emerges as the temperature approaches 700 °C. As the brittle minerals, for instance, carbonates, decrease with temperature, a brittle-ductile transition happens in shale. This work provides very meaningful results different from that at low temperatures to help people better understand the effects of high temperatures in many fields, such as explosive fracturing and radioactive waste disposal.

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“…For the current steady-state modeling efforts, temperature invariant uniform thermal expansion coefficients obtained from the literature [39,40] were used for the granitoid and sedimentary units, as summarized in Tables 2 and 3.…”

Section: Thermal Propertiesmentioning

confidence: 99%

A Reference Thermal-Hydrologic-Mechanical Native State Model of the Utah FORGE Enhanced Geothermal Site

et al. 2021

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The Frontier Observatory for Research in Geothermal Energy (FORGE) site is a multi-year initiative funded by the U.S. Department of Energy for enhanced geothermal system research and development. The site is located on the margin of the Great Basin near the town of Milford, Utah. Work has so far resulted in the compilation of a large amount of subsurface data which have been used to improve the geologic understanding of the site. Based on the compiled data, a three-dimensional geologic model describing the structure, composition, permeability, and temperature at the Utah FORGE site was developed. A deep exploratory well (Well 58-32) and numerous tests conducted therein provide information on reservoir rock type, temperature, stress, permeability, etc. Modeling and simulation will play a critical role at the site and need to be considered as a general scientific discovery tool to elucidate the behavior of enhanced geothermal systems and as a deterministic (or stochastic) tool to plan and predict specific activities. This paper will present the development of a reference native state model and the calibration of the model to the reservoir pressure, temperature, and stress measured in Well 58-32.

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Thermal Expansion of Triaxially Stressed Mudstone at Elevated Temperatures up to 400°C

Cited by 12 publications

References 39 publications

Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems

Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems

Investigation of the Temperature Dependence of the Chemical–Mechanical Properties of the Wufeng–Longmaxi Shale

A Reference Thermal-Hydrologic-Mechanical Native State Model of the Utah FORGE Enhanced Geothermal Site

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