- Modeling and numerical analysis of granite rock specimen under mechanical loading and fire
- L.L.N. Mambou ; J-M. Ndjaka Bienvenu
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2015 , Volume: 7
- Rock Mechanics ; Discrete Element
- Description
- The effect of ISO 834 fire on the mechanical properties of granite rock specimen submitted to uniaxial loading is numerically investigated. Based on Newton's second law, the rate-equation model of granite rock specimen under mechanical load and fire is established. The effect of heat treatment on the mechanical performance of granite is analyzed at the center and the ends of specimen. At the free end of granite rock specimen, it is shown that from 20 °C to 500 °C, the internal stress and internal strain are weak; whereas above 500 °C, they start to increase rapidly, announcing the imminent collapse. At the center of specimen, the analysis of the internal stress and internal strain reveals that the fire reduces the mechanical performance of granite significantly. Moreover, it is found that after 3 min of exposure to fire, the mechanical energy necessary to fragment the granite can be reduced up to 80%.
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- Numerical analysis of thermal impact on hydro-mechanical properties of clay
- X. Wang ; H. Shao ; J. Hesser ; C. Zhang ; W. Wang. ; O. Kolditz
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2014 , Volume: 6
- Soil Mechanics ; Discrete Element
- Description
- As is known, high-level radioactive waste (HLW) is commonly heat-emitting. Heat output from HLW will dissipate through the surrounding rocks and induce complex thermo-hydro-mechanical-chemical (THMC) processes. In highly consolidated clayey rocks, thermal effects are particularly significant because of their very low permeability and water-saturated state. Thermal impact on the integrity of the geological barriers is of most importance with regard to the long-term safety of repositories. This study focuses on numerical analysis of thermal effects on hydro-mechanical properties of clayey rock using a coupled thermo-mechanical multiphase flow (TH2M) model which is implemented in the finite element programme OpenGeoSys (OGS). The material properties of the numerical model are characterised by a transversal isotropic elastic model based on Hooke's law, a non-isothermal multiphase flow model based on van Genuchten function and Darcy's law, and a transversal isotropic heat transport model based on Fourier's law. In the numerical approaches, special attention has been paid to the thermal expansion of three different phases: gas, fluid and solid, which could induce changes in pore pressure and porosity. Furthermore, the strong swelling and shrinkage behaviours of clayey material are also considered in the present model. The model has been applied to simulate a laboratory heating experiment on claystone. The numerical model gives a satisfactory representation of the observed material behaviour in the laboratory experiment. The comparison of the calculated results with the laboratory findings verifies that the simulation with the present numerical model could provide a deeper understanding of the observed effects.
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- Development of Fracture Networks Through Hydraulic Fracture Growth in Naturally Fractured Reservoirs
- X. Zhang ; R. Jeffrey
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 7
- Year: 2013
- Discrete Element ; Mining
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- Quantitative Evaluation of Completion Techniques on Influencing Shale Fracture ‘Complexity’
- N. Nagel ; F. Zhang ; M. Sanchez-Nagel ; D. Walls
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 25
- Discrete Element ; Mining
- Description
- In many of the active shale plays, the extremely low permeability of the shale means simple,
bi-planar hydraulic fractures do not provide enough surface area to make an economic well.
In these cases, the optimal, economic completion requires stimulation of the natural fracture
system - often called increasing the ‘complexity’ of the stimulation. A number of different
multi-well completion techniques have been proposed to enhance shale complexity. The
‘simul-frac’ technique is where companion wells are stimulated at the same location at the
same time, whereas the ‘zipper-frac’ technique employs companion wells that are stimulated
in staggered locations at the same time. The intention with these techniques is to alter either
or both the stress field and the pore pressure field to enhance the shearing of natural fractures.
In this paper, we present the results of a numerical study to quantitatively evaluate the
effectiveness of multi-well completion techniques, particularly the ‘modified zipper-frac’
technique, to optimize shale completions. The study includes a parametric study of the effects
of in-situ stress conditions, natural fracture orientation and fracture friction, and hydraulic
fracture layout on changing near and far-field natural fracture shear (complexity). Changes in
the stress field, particularly shear stress, are considered the primary means of increasing
fracture complexity. The quantitative results of the study provide a means to optimize the
application and design of different multi-well completion techniques as a function of the
presented parameters. Optimized completion designs mean lower well costs, greater produc‐
tion and, ultimately, improved well economics.
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- Fracture Network Connectivity — A Key To Hydraulic Fracturing Effectiveness and Microseismicity Generation
- F. Zhang ; N. Nagel ; B. Lee ; M. Sanchez-Nagel
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 28
- Discrete Element
- Description
- In this work, the effect of fracture network connectivity on hydraulic fracturing effectiveness
was investigated using a discrete element numerical model. The simulation results show that natural fracture density can significantly affect the hydraulic fracturing effectiveness, which was characterized by either the ratio of stimulated natural fracture area to hydraulic fracture area or the leakoff ratio. The sparse DFN cases showed a flat microseismic distribution zone with few events, while the dense DFN cases showed a complex microseismic map which
indicated significant interaction between the hydraulic fracture and natural fractures. Further,
it was found that the initial natural fracture aperture affected the hydraulic fracturing effectiveness more for the dense natural fracture case than for the sparse (less dense) case. Overall, this work shows that fracture network connectivity plays a critical role in hydraulic fracturing effectiveness, which, in-turn, affects treating pressures, the created microseismicity and corresponding stimulated volume, and well production.
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- The XFEM With An Explicit-Implicit Crack Description For Hydraulic Fracture Problems
- N. Weber ; P. Siebert ; K. Willbrand ; M. Feinendegen ; C. Clauser ; T.P. Fries
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 35
- Discrete Element
- Description
- The Extended Finite Element Method (XFEM) approach is applied to the coupled problem
of fluid flow, solid deformation, and fracture propagation. The XFEM model description of
hydraulic fracture propagation is part of a joint project in which the developed numerical model will be verified against large-scale laboratory experiments. XFEM forms an important basis towards future combination with heat and mass transport simulators and extension to more complex fracture systems. The crack is described implicitly using three level-sets to evaluate enrichment functions. Additionally, an explicit crack representation is used to update the crack during propagation. The level-set functions are computed exactly from the explicit representation. This explicit/implicit representation is applied to a fluid-filled crack in
an impermeable, elastic solid and compared to the early-time solution of a plane-strain hydraulic fracture problem with a fluid lag.
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- An ABAQUS Implementation of the XFEM for Hydraulic Fracture Problems
- Z. Chen
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 36
- Discrete Element
- Description
- A new finite element has been implemented in ABAQUS to incorporate the extended finite
element method (XFEM) for the solution of hydraulic fracture problems. The proposed element includes the desired aspects of the XFEM so as to model crack propagation without explicit remeshing. In addition, the fluid pressure degrees of freedom have been defined on the element to describe the fluid flow within the crack and its contribution to the crack deformation. Thus the fluid flow and resulting crack propagation are fully coupled in a natural
way and are solved simultaneously. Verification of the element has been made by comparing the finite element results with the analytical solutions available in the literature.
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- The Fate of Injected Water in Shale Formations
- H. Jia ; J. McLennan ; M. Deo
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 40
- Discrete Element
- Description
- It is well known that only about a third of water injected for hydraulic fracturing of shales is recovered. It is important to understand the fate of this injected water. The amount of water infiltrating the matrix is determined by a number of parameters such as the pressure differential between the fracture and the matrix, the capillary pressure relationships in the fractures and in the matrix and other petrophysical properties of the formation. In this paper, we provide a breakdown for the various possible water losses depending on the reservoir, fracture and operating parameters. A set of capillary pressure relationships for the formation were first created based on the basic mineralogy and the total organic carbon (TOC) content. Fracture capillary pressure also changed depending on the concentrations and types of proppants in the fractures. Two basic end members can be defined – silicistic and dolomitic with different amounts of TOC. The capillary pressure relationships ranged from oil wet, neutral to water wet. Different porosity and permeability combinations were also
examined. Amounts of water relative to the total amount injected that would infiltrate the formation were compiled as the operating conditions (pressures) and formation properties
changed. This calculation shows that the infiltration due to the various phenomena are not
sufficient to account for the water losses if the formations are strongly oil wet. In addition,
situations where water blockages occur due to these multiphase flow effects were identified
and the loss of productivity due to this phenomenon was quantified both for gas and for oil production. The study was conducted using a discrete-fracture network simulator developed at the University of Utah. A realistic (non-orthogonal) representation of a complex fracture network was employed in the study. Realistic representation of distribution and retention of these aqueous fracturing fluids is essential for optimizing hydraulic fracturing treatment volumes.
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- Three dimensional discrete element simulation of trapdoor unloading and gravity flow of sandy granular material
- R.P. Orense ; M.J. Pender ; Y. Toyosawa ; K. Itoh ; N. Kikkawa
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Tunneling ; Discrete Element
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- Particulate Modeling of Sand Slurry Flow Retardation
- M. Gutierrez ; I. Tomac
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Discrete Element
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- DEM simulation of effect of confining pressure on ballast behaviour
- P.K. Thakur ; B. Indraratna ; J.S. Vinod
- 17th International Conference on Soil Mechanics and Geotechnical Engineering (Alexandria)
- Year: 2009
- Railway Geotechnics ; Discrete Element
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- Assessing the possible development of the Tessina landslide using numerical modelling
- L. Zabuski ; S. Silvano ; F. Tagliavini ; A. Pasuto ; M. Mantovani ; G. Marcato
- Book Title / Journal: International Conference : Landslide Processes - From Geomophologic Mapping to Dynamic Modelling in Strassbourg France
- Year: 2009 , Series: Chapter 3: Landslide modeling - Methods for hazard and risk quantification
- Landslides ; Slope Stability ; Discrete Element
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- Main features of two simple bond contact models for bonded granulates: PFC model and Jiang model
- Mingjing Jiang ; Haibin Yan
- 17th International Conference on Soil Mechanics and Geotechnical Engineering (Alexandria)
- Year: 2009
- Soil Mechanics ; Discrete Element
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- Shortest link method for contact detection in discrete element method
- Jamshid Ghaboussi ; Y.M.A. Hashash ; Erfan G. Nezami ; Dawei Zhao
- International Journal for Numerical and Analytical Methods in Geomechanics 30(8): 783 - 801. John Wiley & Sons Ltd
- Year: 2006
- Discrete Element
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- Distinct element analysis of soil-pipeline interaction in sand under upward movement at deep embedment condition
- S. Yimsiri
- 16th International Conference on Soil Mechanics and Geotechnical Engineering (Osaka)
- Year: 2005
- Finite Element / Finite Difference ; Discrete Element
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