1,721,006 research outputs found
Assessment of rock fracture initiation using acoustic emission
Get PDFDSpace SAF Submission Ingestion Package generated from Vireo submission #14339 on 2019-11-26 at 14:04:18Made available in DSpace on 2019-11-26T20:59:49Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-07-16Embargo set by: Seth Robbins for item 113101
Lift date: 2021-11-26T20:59:54Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 113101 on 2021-11-27T10:15:30Z.It is crucial to understand fracture initiation and propagation in rock as the induced fracture is widely applied in the petroleum industry and rock engineering, and fracture often acts as a precursor to ultimate failure. Due to the relative vast existence of granite and its wide application in tunneling, geothermal systems, and CO2 storage, fracture properties of granite are investigated in this study. Charcoal granite specimens of different sizes and geometries are tested under three- and four-point bending to investigate the effect of these parameters on the dimensions of the fracture process zone measured using acoustic emission (AE) technique. The effects of specimen size, geometry, and loading conditions are found to be more pronounced in the specimens with sizes that are commonly used in the laboratory, while the size effect is predicted to be less significant and eventually negligible as the specimen size increases. It is found that both the fracture process zone length and width increase with the specimen size. In addition, even though the span length is kept the same, the fracture process zone size increases with the increasing specimen depth. Loading condition and specimen geometry also influence the length of the fracture process zone, but have very little effect on its width. Fracture process zone in the post-peak regime is also investigated and found to be approximately constant size. It indicates that the fracture process zone is fully developed at peak load or even prior to it.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-08-01The student, Yi Zhong, accepted the attached license on 2019-07-16 at 09:22.The student, Yi Zhong, submitted this Thesis for approval on 2019-07-16 at 09:34.This Thesis was approved for publication on 2019-07-16 at 10:43
Coupled thermo-hydro-mechanical behavior of glacial tills in shallow geothermal systems
Get PDFIncreasing need of practical engineering applications whereby the ground is used as a thermal reservoir and soils are subjected to thermal gradients, such as shallow geothermal systems, motivated this study. The soil response under representative field conditions upon heating can affect the performance and overall operation of shallow applications, demanding adequate input parameters for an efficient design. Therefore, it is critical to better understand the fluid-saturated behavior of geomaterials, where temperature gradients induce deformations, affect the pore pressure, and might significantly influence the pore fluid flow processes. The purpose of this work is to conduct a multi-physical analysis to characterize the coupled thermo-hydro-mechanical behavior of glacial tills in central Illinois and suggest a constitutive model for describing their short- and long-term behavior.
Four specimens of predominantly fine-grained glacial till were collected in the upper 20 m from a 110-meter deep test borehole drilled for a planned geothermal site at the University of Illinois at Urbana-Champaign. The specimens were tested using a 3.5 MPa GDS Triaxial Cell apparatus connected to pressure volume controllers and external heaters to allow the application and measurement of temperature at 22, 32 and 42°C ± 1.0°C. The testing schedule considered a maximum change of temperature of 20°C, in agreement with the temperature operation range of a typical shallow geothermal system. Monotonic thermal loading was applied to the soil samples to evaluate the thermally induced deformation. Drained and undrained compression, as well as flow tests were performed at different temperatures. Moreover, the time-dependent behavior was evaluated at room and elevated temperatures.
The results revealed a limited temperature dependence for the elastic moduli; while hydraulic conductivity increased upon heating, accounting for the change in viscosity of water resulted in limited change for intrinsic permeability at higher temperatures. Glacial tills subjected to thermal loading showed an expansive volume change resulting in thermal expansion coefficients on the order of 10E-4 /°C. Furthermore, it was noticed that the tendency for time-dependent deformation consistently increased at elevated temperatures emphasizing the importance of including long-term (viscous) material response into the constitutive models dealing with subsurface geotechnical applications.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-12-01The student, Jose V Renjifo Ciocca, accepted the attached license on 2020-12-10 at 21:44.The student, Jose V Renjifo Ciocca, submitted this Thesis for approval on 2020-12-10 at 21:49.This Thesis was approved for publication on 2020-12-11 at 09:49.DSpace SAF Submission Ingestion Package generated from Vireo submission #16113 on 2021-03-04 at 16:33:56Made available in DSpace on 2021-03-05T21:47:36Z (GMT). No. of bitstreams: 2
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Previous issue date: 2020-12-11Embargo set by: Seth Robbins for item 117350
Lift date: 2023-03-05T21:47:41Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemAuthor requested closed access (OA after 2yrs) in Vireo ETD systemLimite
Novel techniques for fracture monitoring in crystalline rock
Get PDFThe study of fracture is necessary in geotechnical engineering for the safe design of structures and application of engineering principles. Fracture plays a significant role in the behavior of rock and structures during failure. Often times, fracture processes observed in the laboratory do not accurately represent what occurs in the field due to the effect that specimen size and loading conditions have on fracture properties, namely, fracture toughness and the size of the fracture process zone. The fracture toughness increases with specimen size until it reaches a limiting value when the material is large enough to exhibit brittle behavior. In a similar manner, the size of the fracture process zone is observed to grow with specimen size until a limiting value is reached for a large enough specimen. In this study, experiments were performed on granitic specimens of different sizes and under two different loading conditions, three-point and four-point bending. Digital Image Correlation (DIC) was used to identify and calculate the dimensions of the fracture process zone. The study of fracture and fracture processes in granitic specimens through DIC is challenging due to the extremely small displacements, in the order of microns, that are associated with fracture in granite. The results from experiments performed on Adelaide Black granite under three-point bending are compared to data obtained using acoustic emission on the same rock and were shown to be in good agreement. It was observed that in Charcoal granite specimens of sizes that that are typically used in the laboratory, the fracture process zone is larger under four-point bending compared to three-point bending conditions. However, it is predicted that for a large enough specimen, the dimensions of the fracture process zone are similar for both loading conditions. In addition, in the appendix, the use of ultrasonic measurements to study and determine the geometry of a propagating hydraulic fracture in granite is described.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-05-01The student, Gabriel Mishaan Lilienthal, accepted the attached license on 2019-04-23 at 11:48.The student, Gabriel Mishaan Lilienthal, submitted this Thesis for approval on 2019-04-23 at 11:49.This Thesis was approved for publication on 2019-04-23 at 17:58.DSpace SAF Submission Ingestion Package generated from Vireo submission #13838 on 2019-08-22 at 16:23:39Made available in DSpace on 2019-08-23T20:48:23Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-04-23Embargo set by: Seth Robbins for item 112370
Lift date: 2021-08-23T20:48:32Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 112370 on 2021-08-24T09:15:31Z
Machine learning approaches for enhanced analyses of rock properties in geologic CO2 storage
Get PDFSubmission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2025-08-01The student, Ekaterina Barteneva, accepted the attached license on 2023-07-21 at 11:49.The student, Ekaterina Barteneva, submitted this Thesis for approval on 2023-07-21 at 12:06.This Thesis was approved for publication on 2023-07-21 at 14:44.DSpace SAF Submission Ingestion Package generated from Vireo submission #19775 on 2023-12-04 at 17:18:55Geological carbon storage (GCS) has emerged as a promising approach for mitigating the accumulation of carbon dioxide (CO2) in the atmosphere. This research investigates the application of machine learning (ML) techniques to enhance the analysis and optimization of CO2 storage operations. The initial part of the study focuses on predicting permeability and breakthrough pressure in the caprock, the upper layer of GCS. By conducting a thorough literature review and developing robust ML algorithms, accurate predictions are achieved using input variables derived from the comprehensive datasets. Prediction of the CO2 breakthrough pressure is performed using three ML methods: the non-linear neural network, Bayesian framework, and the classification model are developed and evaluated for their accuracy and reliability. The analysis includes direct and indirect test results with two (porosity and permeability) and five (porosity, permeability, specific surface area, pore radius, and clay content) input parameter configurations. The results reveal strong correlations between the predicted and measured breakthrough pressure values. The non-linear neural network model demonstrates a superior performance when utilizing five input parameters, while the Bayesian framework yields identical predictions for both two-parameter and five-parameter configurations. The classification model successfully captures the correct range of values in its predictions for both configurations. The machine learning techniques are also utilized to analyze wellbore data and acoustic emission waveforms. Fractured wellbore intervals are predicted based on petrophysical and mineralogical parameters, underscoring the importance of considering multiple parameters for accurate fracture characterization. The analysis of acoustic emission waveforms demonstrates the effectiveness of deep learning models in denoising seismic data and accurately predicting the first arrival time. The findings of this study contribute to a better understanding of the correlation between the rock properties that are crucial for the analysis of the geologic CO2 storage. This work highlights the potential of ML approaches in robust assessment of caprock sealing capacity, enhancement of the quality of the seismic data interpretation, and efficient detection of the fractured intervals based on the wellbore log data
Geomechanical analysis of the influence of CO2 injection location on fault stability
Get PDFLarge amounts of carbon dioxide (CO2) should be injected in deep saline formations to mitigate climate change, implying geomechanical challenges that require further understanding. Pressure build-up induced by CO2 injection will decrease the effective stresses and may affect fault stability. Geomechanical effects of overpressure induced by CO2 injection either in the hanging wall or in the foot wall on fault stability are investigated. CO2 injection in the presence of a low-permeable fault induces pressurization of the storage formation between the injection well and the fault. The low permeability of the fault hinders fluid flow across it and leads to smaller overpressure on the other side of the fault. This variability in the fluid pressure distribution gives rise to differential total stress changes around the fault that reduce its stability. Despite a significant pressure build-up induced by the fault, caprock stability around the injection well is not compromised and thus, CO2 leakage across the caprock is unlikely to happen. The decrease in fault stability is similar regardless of the side of the fault where CO2 is injected. Simulation results show that fault core permeability has a significant effect on fault stability, becoming less affected for high-permeable faults. An appropriate pressure management will allow storing large quantities of CO2 without inducing fault reactivation. © 2016 Institute of Rock and Soil Mechanics, Chinese Academy of SciencesThe first author acknowledges the support from the “EPFL Fellows” fellowship program co-funded by Marie Curie, FP7 (Grant No. 291771) and partial support from the “TRUST” project of the European Community's Seventh Framework Programme FP7/2007–2013 (Grant No. 309607) and the “FracRisk” project of the European Community's Horizon 2020 Framework Programme H2020-EU.3.3.2.3 (Grant No. 640979). Activities of the second author are sponsored by SCCER-SoE (Switzerland) (Grant No. KTI.2013.288) and Swiss Federal Office of Energy (SFOE) project CAPROCK (Grant No. 810008154). This publication has also been produced with partial support from the BIGCCS Centre (for the third author), performed under the Norwegian research program Centers for Environment-friendly Energy Research (FME). The third author acknowledges the following partners for their contributions: Gassco, Shell, Statoil, TOTAL, ENGIE, and the Research Council of Norway (193816/S60).Peer reviewe
Assessment of rock fracture initiation using acoustic emission
No full textIt is crucial to understand fracture initiation and propagation in rock as the induced fracture is widely applied in the petroleum industry and rock engineering, and fracture often acts as a precursor to ultimate failure. Due to the relative vast existence of granite and its wide application in tunneling, geothermal systems, and CO2 storage, fracture properties of granite are investigated in this study. Charcoal granite specimens of different sizes and geometries are tested under three- and four-point bending to investigate the effect of these parameters on the dimensions of the fracture process zone measured using acoustic emission (AE) technique. The effects of specimen size, geometry, and loading conditions are found to be more pronounced in the specimens with sizes that are commonly used in the laboratory, while the size effect is predicted to be less significant and eventually negligible as the specimen size increases. It is found that both the fracture process zone length and width increase with the specimen size. In addition, even though the span length is kept the same, the fracture process zone size increases with the increasing specimen depth. Loading condition and specimen geometry also influence the length of the fracture process zone, but have very little effect on its width. Fracture process zone in the post-peak regime is also investigated and found to be approximately constant size. It indicates that the fracture process zone is fully developed at peak load or even prior to it.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste
Laboratory-Scale Assessment of CO2 Sealing Potential of Heterogeneous Caprock
No full textGeologic carbon storage is widely recognized as a critical strategy for mitigating atmospheric carbon dioxide (CO2) levels, yet its effectiveness is contingent upon the integrity of caprock formations that prevent CO2 leakage. This study investigates the sealing potential of three representative caprock formations—Eau Claire Shale, Maquoketa Shale, and Opalinus Clay—by employing a comprehensive set of experimental approaches. Laboratory assessments include permeability tests, stepwise CO2 injection, imbibition experiments, and porosimetry-based estimation to evaluate the sealing potential of heterogeneous geomaterials. It appears that within each formation, sand-rich specimens exhibit significantly higher permeability and lower breakthrough pressures compared to their clay-rich counterparts, underscoring the influence of the lithological variation. An indirect method based on pore structure analysis tends to underestimate the sealing capacity, highlighting discrepancies caused by the confinement, pore structure anisotropy, and variations in geochemical interactions. A statistical analysis based on the data set from this study and the literature reveals that CO2 breakthrough pressure is positively correlated with the clay content, negatively correlated with the permeability and dominant pore size, and independent of its porosity. The sealing number is introduced to provide a quantitative framework for evaluating the sealing integrity of the tested caprock formations to withstand buoyant forces. This study highlights the critical role of heterogeneities in determining caprock sealing potential and emphasizes the importance of direct measurements, particularly the use of the stepwise method, for accurate assessment. Advanced imaging and geophysical monitoring, coupled with multi-scale experiments, are recommended to enhance the reliability of heterogeneous caprock integrity assessments.H.K. and R.M. acknowledge support from the U.S. National Science Foundation Faculty Early Career Development Program CMMI-2239630. The caprock cores are provided by the Illinois State Geological Survey and swisstopo. V.V. acknowledges funding from the European Union's Horizon Europe Research and Innovation Programme through the Doctoral Network of the Marie Sklodowska-Curie Actions SMILE (https://smile-msca-dn.eu/), under Grant 101073281. IMEDEA is an accredited “Maria de Maeztu Excellence Unit” (Grant CEX2021-001198, funded by MICIU/AEI/10.13039/501100011033).With funding from the Spanish government through the "Maria de Maeztu Centre of Excellence" accreditation (CEX2021-001198).Peer reviewe
Subcritical time-dependent response of Berea sandstone
Get PDFWith the increasing development of underground engineering projects in rock formations, construction and storage activities introduce stress disturbances within the subsurface layers. The response of rocks to these disturbances unfolds over extended periods, sometimes spanning months to years, giving rise to time-dependent deformation. Laboratory- and field-scale observations indicate that such time-dependent behavior can lead to significant changes in material properties, as well as the formation of micro- and macro-cracks within the intact rock. The presence of in-situ pore fluids further complicates the process by promoting the crack growth due to stress corrosion cracking and modifying the stress field during the diffusion process. All of these factors pose additional and unpredictable risks to engineering stability, even before the material reaches its apparent strength limit.
In this study, the constitutive model describing poro-visco-elasto-plastic behavior of a fluid-saturated rock is adopted. Inelastic time-dependent deformation of Berea sandstone is evaluated in the compression tests, with a stepwise loading method applied. To assess time-dependent behavior, axial and lateral strains are measured during uniaxial compression, as well as triaxial drained and undrained compression tests. Both shear and bulk viscosity are calculated to track changes across different loading stages. Additionally, acoustic emission is monitored throughout each experiment to observe the evolution of microcracks as the load increases. The evolution of permeability (closely related to deformation of the pore space) is also recorded at different stages of loading. This set of interrelated attributes offers a comprehensive and reliable characterization of the fundamental principles governing time-dependent deformation in rocks under different boundary conditions.
This study indicates that creep exhibits a linear trend at low-pressure stages, while, when deviatoric stress reaches 80% of the ultimate load-bearing capacity, all measured indicators show significant changes. Shear viscosity and bulk viscosity decrease with increase in deviatoric stress and this tendency accelerates while approaching failure. Permeability also decreases throughout the test and during each creep stage due to the compaction of the specimens. The acoustic emission activity, in general, is found to be well correlated with the loading stages during the creep tests, accelerating closer to failure. The findings of this study can be used for the assessment of subcritical behavior of rock under different drainage conditions.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-10-19 without embargo termsThe student, Shirui Ding, accepted the attached license on 2024-12-13 at 16:37.The student, Shirui Ding, submitted this Thesis for approval on 2024-12-13 at 16:49.This Thesis was approved for publication on 2024-12-16 at 11:45.DSpace SAF Submission Ingestion Package generated from Vireo submission #21598 on 2025-10-19 at 18:08:3
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