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Collaborating Authors
Well Completion
For the past four decades, plenty of researches and practices have been executed on EGS. A systematic review of existing EGS projects was provided by Breede et al. which transpires that EGS is still on a learning curve (Breede et al., 2013). One major challenge for EGS development is to improve the hydraulic performance of reservoir, whose natural permeability is very low. Therefore, hydraulic stimulation has been an essential operation to increase the reservoir permeability. Basically, hydrofracturing and hydroshearing concepts have been tested over the previous EGS developing experience and most of the field tests and observations support the idea of hydroshearing (Jung, 2013). However, hydrofracturing mechanism cannot be excluded. Some of the field stimulation tests indicated hydraulic fracturing did occur, for example stimulation of Jolokia#1 well in Cooper Basin EGS Project, Australia and stimulation of Gt GrSk 4/05 well in Groschonebeck EGS site, Germany (Zimmerman et al., 2008). Actually, generation of new fractures by hydraulic fracturing is still necessary to connect natural fractures in case that there is no natural fracture to directly cross the pressurized injection interval (Ito & Hayashi, 2003). Compared with common hydraulic fracturing in hydrocarbon field, there are at least three distinctive features in terms of hydraulic fracturing conditions in EGS stimulation: 1) EGS well is usually completed with a long open section with interval of tens to hundreds of meters; 2) isolation packer application is very limited and 3) deviated well design with varying well trajectory can be adopted to favor heat extraction.
- Oceania > Australia > Queensland (0.34)
- Oceania > Australia > South Australia (0.24)
- Energy > Renewable > Geothermal > Geothermal Resource (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource for Power Generation > Enhanced Geothermal System (0.42)
- Oceania > Australia > South Australia > Cooper Basin (0.99)
- Oceania > Australia > Queensland > Cooper Basin (0.99)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Abstract In order to understand the mechanics of hydraulic fracturing considering the fluid viscosity and the fluid injection rate, a series of experiments for hydraulic fracturing were performed in laboratory condition. Four kinds of fluid (1, 100, 500, 1000 cSt) were injected at various flow rate (2, 10, 50 ml/min). Bonded particle model with hydro-mechanical coupling analysis was validated to simulate hydraulic fracturing and numerical moment tensor inversion technique was applied to simulation to investigate the mechanism of microcracking of hydraulic fracturing. The effect of the fluid viscosity and the injection rate are closely associated with the fluid infiltration and the crack growth. When a low viscosity fluid or a low injection rate is used, the fluid infiltration can easily occur. The hydraulic fracturing process and the effect of fluid infiltration can be successfully reproduced by a bonded particle model.
- North America > United States (0.28)
- Asia > Japan (0.18)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.97)
Abstract To satisfy the need for development of transportation infrastructure, hydropower, water supply, etc., more long, deep, and large diameter tunnels and underground caverns are being, or will be, constructed in China. Commonly, they may be characterised as being under heavy overburden, of complicated engineering design, under difficult geological conditions, requiring sophisticated project management, etc. This keynote address presents an overview of some practical challenges, recent developments, and technical progress, based on lessons learned from successful construction of deep headrace tunnels at Jinping II hydropower station. Geomechanical challenges overcome during construction are reviewed and summarised: these include the control of large deformations or soft rock squeezing, the prediction of, and risk mitigation against, severe rock-bursts, the forecasting and treatment of high pressure groundwater with associated flow issues, etc. Some innovative and effective analysis methods and engineering approaches are illustrated: they were applied to overcome the aforementioned underground engineering hazards. The experience accumulated during the construction of the tunnels at Jinping II hydropower station provides a valuable reference for similar projects in the future.
- Geology > Rock Type > Sedimentary Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Hydroelectric (0.93)
- Energy > Power Industry > Utilities (0.93)
- Materials > Metals & Mining (0.68)
Abstract The paper presents a numerical procedure based on Smoothed Particle Hydrodynamics (SPH) framework to analyze the fracture and fragmentation process of rock medium under dynamic stress wave followed by gas expansion. To analyze the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation, a rectangular rock mass with/without rock joint containing a single centrally located source of explosive were numerically blasted in the proposed SPH framework. This paper uses modified Grady-Kipp continuum damage model to analyze dynamic fracture behavior of rock mass in tension due to blast loading. For shear failure, Drucker-Prager yield criterion with associative rule is employed in the constitutive model for plastic deformation. The damage pattern around the blasthole and the formation of tensile cracks near free surfaces were subsequently simulated using the developed numerical tool. It is found that the developed procedure has the potential to provide valuable information to understand the physical phenomena those occur in the failure process of rock mass under blast induced dynamic loads.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.31)
Abstract This paper proposes a new continuum damage model accounting for inertial effects (Keita et al 2014) to analyze the fracture behavior of rock in tension due to blasting. The two-scale damage model is fully deduced from small-scale descriptions of dynamic micro-cracks propagation under tensile loading (mode I). An appropriate micro-mechanical energy analysis is combined with homogenization based on asymptotic developments in order to obtain the macroscopic evolution law for damage (Dascalu et al 2008). The global macroscopic response predicted by the model is obtained by implementation of the dynamic damage law in a transient finite elements code. The damage pattern around the blasthole was simulated. Numerical simulations were able to illustrate the ability of the model to reproduce the radial cracks zone due to rock blasting. The influences of microstructural size and of micro-cracks orientation on damage distribution around the blasthole have been determined.
- Data Science & Engineering Analytics > Information Management and Systems (0.67)
- Reservoir Description and Dynamics (0.52)
- Well Completion > Hydraulic Fracturing (0.47)
Study on the Natural Fracture’s Effect on Hydraulic Crack’s Propagation in Coal Seam
Song, Chenpeng (State Key Laboratory of Coal Mine Disaster Dynamics and Control) | Lu, Yiyu (State Key Laboratory of Coal Mine Disaster Dynamics and Control) | Jia, Yunzhong (State Key Laboratory of Coal Mine Disaster Dynamics and Control)
Abstract To investigate the natural fracture's effect on hydraulic fracturing crack propagation in the coal seam, the two-dimensional model of hydraulic fracturing crack intersecting natural fractures is built. Based on it, the laws of crack propagation and failure mechanism of natural fractures are studied by using the method of theoretical analysis and numerical simulation. The research suggests that angle of interaction between main crack and natural fracture, the horizontal differential principal stress and the development degree of natural fractures are the three main factors that affect direction of crack propagation. The direction of the propagation of crack tends along natural fracture due to shear failure in condition of low horizontal differential principal stress and low angle of interaction; Besides, with the increase of horizontal differential principal stress or angle of interaction, the propagating fracture tends to cross the natural fracture. The small size of natural fracture had little or no effect on the direction of the propagation of hydraulic fracture whereas the propagating fracture turns to natural fracture's direction when the size of natural fracture is large.
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
Abstract While the fracture (rupture) dynamics of strike-slip earthquakes has been clarified to a practically acceptable level, the mechanical characteristics of shallow dip-slip seismic events remain unexplained owing to the shortage of the near-field seismological observations and the analytical difficulties at the rupture tip of an interface (fault plane) in the proximity of a free surface. In this contribution, utilizing the techniques of finite difference modeling and dynamic photoelasticity, the fracture dynamics of a dip-slip fault plane located near a free surface is studied numerically as well as experimentally. Each two-dimensional fracture model may contain a flat fault plane (initially welded interface) that dips either vertically or at an angle (e.g. 45 degrees) in a monolithic linear elastic medium (representing rocks). The time-dependent development of wave field associated with the crack-like rupture along every fault plane is recorded. Both numerical and experimental observations indicate when the fault rupture that is initiated at some depth approaches the free surface, four Rayleigh-type waves are produced. Two of them move along the free surface as Rayleigh surface waves into the opposite directions (in the hanging wall or footwall) to the far field, and the other two propagate back downwards along the fractured interface into depth. These downward interface waves may considerably govern the stopping phase of the dynamic fracture, and according to the seismological recordings, they seem to have existed during the rupture process of the 2011 off the Pacific coast of Tohoku, Japan, earthquake. In the case of an inclined fault plane, the interface and Rayleigh waves interact with each other and a shear wave possessing concentrated energy (corner wave) is generated and causes stronger disturbances in the hanging wall. The existence of the downward interface and corner waves, first numerically predicted in 2005 by Uenishi and Madariaga, seems to have been confirmed by this series of laboratory fracture experiments.
- North America > United States (0.70)
- Asia > Japan > Tōhoku (0.25)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Structural Geology > Fault (1.00)
- North America > United States > Wyoming > Great Basin (0.99)
- North America > United States > Utah > Great Basin (0.99)
- North America > United States > Oregon > Great Basin (0.99)
- (3 more...)
Abstract A hybrid finite-discrete element method is introduced to simulate dynamic fracture of rock and resultant fragment arching caused by rock blast. Three typical examples, i.e. blast in a rock mass with a single borehole and a free surface, simultaneous blast, and consecutive blast with various delay times, are modelled and the obtained stress wave propagation, fracture process and resultant fragment movement are compared with those well documented in literatures. It is found that the hybrid finite-discrete element method reproduces the dynamic fracture of rock in rock blast from the stress wave propagation to the formations of crushed zone and cracked zone around the boreholes, the propagation of long radial cracks resulting in rock fracture, the casting of resultant fragments into air, and the fragment arching. It is concluded that the hybrid finite-discrete element method is a valuable numerical tool for the study on rock blast and a more advanced numerical method compared with the finite element method or discrete element method in terms of modelling dynamic fracture of rock.
Observation of Fracture Process of Rocks Subjected to Freeze-Thaw Cycles Using X-ray CT
Kodama, J. (Hokkaido University) | Nakaya, M. (Hazama-ando Co. Ltd.) | Nara, Y. (Tottori University) | Goto, T. (Muroran Institute of Technology) | Fukuda, D. (Hokkaido University) | Fujii, Y. (Hokkaido University) | Kaneko, K. (Horonobe Institute for the Subsurface Environment Technology)
Abstract Understanding fracture process of rocks exposed to freeze-thaw cycles is a fundamental issue for stability assessment of a rock fill dam as well as a rock slope, especially in cold weather regions. In this study, cyclic freeze-thaw tests were carried out on rock samples in order to characterize fracture propagation by freeze-thaw action. The fracture process was characterized by macroscopic observation by digital camera and changes in water absorption. Fracture initiation and propagation inside of the specimen were also observed using X-ray CT scanner. It was found that the fracture process depends on the rock type. For rocks which possess preferred orientation of pre-existing fractures and remarkable anisotropy in P-wave velocity, only one fracture propagated dominantly and split the rock specimen in half. Gradual increase in aperture of the fracture was observed not only on surfaces but also inside of the specimen. On the other hand, for isotropic rock, propagation and branching of several fractures occurred and rock samples were split into several parts. These fracture processes were confirmed by change in water absorption. Water absorption of the anisotropic rock tended to increase gradually with freeze-thaw cycles, but suddenly decreased to the initial value at the occurrence of split. In contrast, water absorption of the isotropic rock continued to increase even after sample split occurred.
- Energy > Oil & Gas > Upstream (0.74)
- Health & Medicine (0.57)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.75)
Abstract The strength and the energy required for rock fracturing depend on the strain rate. However, the strain rate dependence of them under dynamic loading has not yet been fully understood. In this study, the author conducted static and impact three-point bending tests on specimens of andesite and gabbro, and explored the effect of strain rate on the bending strength and the absorbed energy required for fracturing. As a result of the tests, the bending strength of the rocks linearly increased from ca. 20 to 80 MPa with increase of the strain rate from 10 to ca. 50 s. The absorbed energy required for fracturing also increased from ca. 0.5 to 15 J per unit area with the increase of the strain rates. It increased rapidly and linearly with the strain rate in the strain rate region above 20 s. This change in the relationship between the strain rate and the absorbed energy required for fracturing would reflect a transition of the fracturing mechanism from the thermo-activation to the macro-viscosity.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)