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1
Schoenberg, Michael, and Colin M. Sayers. "Seismic anisotropy of fractured rock." GEOPHYSICS 60, no. 1 (January 1995): 204–11. http://dx.doi.org/10.1190/1.1443748.
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A simple method for including the effects of geologically realistic fractures on the seismic propagation through fractured rocks can be obtained by writing the effective compliance tensor of the fractured rock as the sum of the compliance tensor of the unfractured background rock and the compliance tensors for each set of parallel fractures or aligned fractures. The compliance tensor of each fracture set is derivable from a second rank fracture compliance tensor. For a rotationally symmetric set of fractures, the fracture compliance tensor depends on only two fracture compliances, one controlling fracture compliance normal, the other, tangential, to the plane of the fractures. The stiffness tensor, which is more useful in the consideration of elastic wave propagation through rocks, can then be obtained by inversion. The components of the excess fracture compliance tensor represent the maximum amount of information that can be obtained from seismic data. If the background rock is isotropic and the normal and shear compliance of each fracture are equal, although different from those of other fractures, the effective elastic behavior of the fractured rock is orthorhombic for any orientation distribution of fractures. A comparison of the theory with recent ultrasonic experiments on a simulated fractured medium shows near equality of the normal and shear compliance for the case of air‐filled fractures.
2
Roshankhah, Shahrzad, Arman K. Nejad, Orlando Teran, and Kami Mohammadi. "Modelling the variation in the behaviour of pre-fractured rocks subjected to hydraulic fracturing with permeability of the rock matrix using finite-discrete element method." E3S Web of Conferences 205 (2020): 08001. http://dx.doi.org/10.1051/e3sconf/202020508001.
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In this study, we present the results of two-dimensional numerical simulations for the effects of rock matrix permeability on the behaviour of hydraulic fractures in intact and pre-fractured rocks. The simulations are performed using the Finite-Discrete Element Method (FDEM). In this method, the deformation and fluid pressure fields within the porous rock blocks, pre-existing fracture network, and hydraulically induced fractures are calculated through a fully coupled hydromechanical scheme. Furthermore, new fractures can initiate in crack elements located between each pair of finite elements and can propagate in any path that the boundary and loading conditions require according to non-linear fracture mechanics criteria. Fluid channels are also defined between pairs of finite elements simulating the inter-connected flow paths through porous media. Four models of the rock mass are created in this study: (i) homogeneous-impermeable, (ii) homogeneous-permeable, (iii) heterogeneous-impermeable matrix, and (iv) heterogeneous-permeable matrix. Heterogeneous rock masses contain a discrete fracture network (natural fractures) in the rock mass structure. Hydraulic fracturing is modelled in domains of 40×40 m2 with the four different structures and mass transport capacities, and the results are compared to each other. The results highlight the significant effect of diffusive fluid flow through rock blocks, in addition to the flow through fracture network, on the global hydromechanical behaviour of the rock mass. These results help to understand the governing hydromechanical processes taking place in fractured rocks with matrix of different permeability, such as granites, shales, carbonate rocks, and sandstones and the extent of complexities required to model their behaviour to achieve reasonable accuracy.
3
Wang, E. Z., Z. Q. Yue, L. G. Tham, Y. Tsui, and H. T. Wang. "A dual fracture model to simulate large-scale flow through fractured rocks." Canadian Geotechnical Journal 39, no. 6 (December 1, 2002): 1302–12. http://dx.doi.org/10.1139/t02-068.
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Discrete fracture network models can be used to study groundwater flow in fractured rock masses. However, one may find that it is not easy to apply such models to practical projects as it is difficult to investigate every fracture and measure its hydraulic parameters. To overcome such difficulties, a dual fracture model is proposed. Taking into account the hydraulic characteristics of the various elements of the fracture system, a hydrogeological medium is assumed to consist of two components: the dominant fracture network and the fractured rock matrix. As the dominant fracture network consists of large fractures and faults, it controls the groundwater flow in rock masses. Depending on the permeabilities of the in-fill materials, these fractures and faults may serve as channels or barriers of the flow. The fractured rock matrix, which includes rock blocks and numerous small fractures, plays a secondary role in groundwater flow in such medium. Although the small fractures and rock blocks possess low permeability, their numbers and their total porosity are relatively large. Therefore, they provide large volume for groundwater storage. In this paper, the application of the proposed model to simulate the groundwater flow for a hydropower station before and after reservoir storage is reported. The implications of the results on the design of the station are also highlighted.Key words: seepage flow, dual fracture model, dominant fracture, fractured rock matrix, case studies, rock-filled dam.
4
LV, WEIFENG, GUOLIANG YAN, YONGDONG LIU, XUEFENG LIU, DONGXING DU, and RONG WANG. "EFFECT OF FRACTAL FRACTURES ON PERMEABILITY IN THREE-DIMENSIONAL DIGITAL ROCKS." Fractals 27, no. 01 (February 2019): 1940015. http://dx.doi.org/10.1142/s0218348x19400152.
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The fracture has great impact on the flow behavior in fractured reservoirs. Fracture traces are usually self-similar and scale-independent, which makes the fractal theory become a powerful tool to characterize fracture. To obtain three-dimensional (3D) digital rocks reflecting the properties of fractured reservoirs, we first generate discrete fracture networks by stochastic modeling based on the fractal theory. These fracture networks are then added to the existing digital rocks of rock matrixes. We combine two low-permeable cores as rock matrixes with a group of discrete fracture networks with fractal characteristics. Various types of fractured digital rocks are obtained by adjusting different fracture parameters. Pore network models are extracted from the 3D fractured digital rock. Then the permeability is predicted by Darcy law to investigate the impacts of fracture properties to the absolute permeability. The permeability of fractured rock is subject to exponential increases with fracture aperture. The relationship between the permeability and the fractal dimension of fracture centers is exponential, as well as the relationship between permeability and the fractal dimension of fracture lengths.
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Xu, Chaoshui, Shaoqun Dong, Hang Wang, Zhihe Wang, Feng Xiong, Qinghui Jiang, Lianbo Zeng, Leon Faulkner, Zhao Feng Tian, and Peter Dowd. "Modelling of Coupled Hydro-Thermo-Chemical Fluid Flow through Rock Fracture Networks and Its Applications." Geosciences 11, no. 4 (March 29, 2021): 153. http://dx.doi.org/10.3390/geosciences11040153.
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Most rock masses contain natural fractures. In many engineering applications, a detailed understanding of the characteristics of fluid flow through a fractured rock mass is critically important for design, performance analysis, and uncertainty/risk assessment. In this context, rock fractures and fracture networks play a decisive role in conducting fluid through the rock mass as the permeability of fractures is in general orders of magnitudes greater than that of intact rock matrices, particularly in hard rock settings. This paper reviews the modelling methods developed over the past four decades for the generation of representative fracture networks in rock masses. It then reviews some of the authors’ recent developments in numerical modelling and experimental studies of linear and non-linear fluid flow through fractures and fracture networks, including challenging issues such as fracture wall roughness, aperture variations, flow tortuosity, fracture intersection geometry, fracture connectivity, and inertia effects at high Reynolds numbers. Finally, it provides a brief review of two applications of methods developed by the authors: the Habanero coupled hydro-thermal heat extraction model for fractured reservoirs and the Kapunda in-situ recovery of copper minerals from fractures, which is based on a coupled hydro-chemical model.
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Han, Tongcheng, and Sam Yang. "Dielectric properties of fractured carbonate rocks from finite-difference modeling." GEOPHYSICS 84, no. 1 (January 1, 2019): MR37—MR44. http://dx.doi.org/10.1190/geo2018-0003.1.
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Fractures are common features in virtually all types of geologic rocks and tend to dominate their mechanical and hydraulic properties. Detection and characterization of fractures in rocks are of interest to a variety of geophysical applications. We have investigated the frequency-dependent dielectric properties of fractured porous carbonate rocks in the frequency range [Formula: see text] and their relationships with different types of fluids filling the fractures, fracture connectivity, and directions of electrical field applied to the rocks using numerical simulation methods based on a 3D finite-difference model. We tested the validity of the modeling method on a spherical-shell model with the theoretical analytical solutions. The two fractures in the two digital carbonate rocks have the same length, but in one rock, they intersect and in the other sample they do not. The fractures in the brine-saturated digital rocks are filled either with oil or with the same brine as in the background rock. We found that although conductivity and relative permittivity are sensitive to the fracture-filling fluids, the dielectric loss factor is the best parameter discriminating the fluids. When filled with brine, the fracture connectivity does not affect the dielectric properties of the rocks. When filled with oil, the fracture connectivity can only be detected if the electrical field is parallel to the longer fracture orientation. The results provide new insights into the frequency-dependent dielectric responses of fractured sedimentary rocks and will help with the interpretation of the dielectric data acquired from rocks with fractures.
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Pan, Bin, and Yang Song Zhang. "Searching for the Shortest Seepage Path of 3D Network in Fractured Rock Masses." Applied Mechanics and Materials 580-583 (July 2014): 857–61. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.857.
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Fractured rock is a combination of rocks and fractures,the fractures which are ubiquitously distributed in fractured rock mass often constitute the flow and migration path of underground fluid and radionuclide.Discrete Fracture Network Model (DFN) was built with in-situ observations to evaluate the hydraulic conductivity tensor of rock masses.The fractures relation pattern with corresponding algorithm is given on the basis of computational geometric,and then the graph theory is employed as the mathematical model to represent the mutual positional relation of fractures.And then,with the use of Dijkstra algorithm, the hydraulic conductivity tensor could be obtained.
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Jiang, Lu, and Yang Song Zhang. "The Research on Mean Spacing of Rock Fracture." Applied Mechanics and Materials 580-583 (July 2014): 219–23. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.219.
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The mean spacing of rock fracture is a very important parameter base to evaluate rock mass,a number of rock studies base on it. Object of this paper is Beishan preselected area in Gansu Province, China. A uthor use GPS-RTK to measure the fracture’s endpoints and inflection, then process the resulting coordinate, building a three-dimensional model of rock fracture by using three-dimensional software and meshing the three-dimensional model, Through the analysis of fractures in each grid to calculate the linear density of rock fracture, after the orientation and inclination correction on linear density, it can be converted to an mean spacing of rock fractures. The mean spacing of rock fracture can be directly used for rock mass classification in GSI rock systems, and has a great significance in rock engineering studies.
9
Sicking, Charles, and Peter Malin. "Fracture Seismic: Mapping Subsurface Connectivity." Geosciences 9, no. 12 (December 6, 2019): 508. http://dx.doi.org/10.3390/geosciences9120508.
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Fracture seismic is the method for recording and analyzing passive seismic data for mapping the fractures in the subsurface. Fracture seismic is able to map the fractures because of two types of mechanical actions in the fractures. First, in cohesive rock, fractures can emit short duration energy pulses when growing at their tips through opening and shearing. The industrial practice of recording and analyzing these short duration events is commonly called micro-seismic. Second, coupled rock–fracture–fluid interactions take place during earth deformations and this generates signals unique to the fracture’s physical characteristics. This signal appears as harmonic resonance of the entire, fluid-filled fracture. These signals can be initiated by both external and internal changes in local pressure, e.g., a passing seismic wave, tectonic deformations, and injection during a hydraulic well treatment. Fracture seismic is used to map the location, spatial extent, and physical characteristics of fractures. The strongest fracture seismic signals come from connected fluid-pathways. Fracture seismic observations recorded before, during, and after hydraulic stimulations show that such treatments primarily open pre-existing fractures and weak zones in the rocks. Time-lapse fracture seismic methods map the flow of fluids in the rocks and reveal how the reservoir connectivity changes over time. We present examples that support these findings and suggest that the fracture seismic method should become an important exploration, reservoir management, production, and civil safety tool for the subsurface energy industry.
10
Lyu, XianZhou, Zenghui Zhao, Xiaojie Wang, and Weiming Wang. "Study on the Permeability of Weakly Cemented Sandstones." Geofluids 2019 (January 15, 2019): 1–14. http://dx.doi.org/10.1155/2019/8310128.
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Fractured rocks are a type of complex media that widely exist in various projects including energy, hydraulic, and underground space engineering, whose permeability properties are a hotspot in current rock mechanics domain. Aiming at investigating the seepage characteristics of the fracture surfaces in different rock strata, uniaxial compressive test and permeability test were performed on single-fracture homogenous and heterogeneous rocks. Specifically, rock’s physical and mechanical parameters were measured in uniaxial tests while the initial width of the single fracture was determined through CT scanning. In combination with test results and the calculation model of the displacement of single-fracture heterogeneous rock under triaxial stress condition, the calculation formula of the permeability coefficient of single-fracture heterogeneous rock was derived. Results show that hydraulic pressure in the fracture can affect the permeability coefficient of the fractured rock. Hydraulic fracturing effect occurred with the increase of hydraulic pressure in the fracture, which then generates slight normal deformations of the rock masses on both two sides of the fracture surface, decreases the contact area in the fracture, and leads to the increases of both fracture width and permeability coefficient. For single-fracture rock, the lithological properties of the rock masses on both two sides of the fracture surface impose significant effects on the permeability coefficient. Under same hydraulic pressure and confining pressure, the permeability coefficient of single-fracture coarse sandstone is greatest, followed by that of single-fracture heterogeneous rock, and finally by single-fracture fine sandstone. Theoretical calculation results agree well with the test results, suggesting that the derived theoretical formula can adequately describe the variation tendencies of permeability coefficient with confining pressure and hydraulic pressure in the fracture.
11
Stesky, R. M. "Electrical conductivity of brine‐saturated fractured rock." GEOPHYSICS 51, no. 8 (August 1986): 1585–93. http://dx.doi.org/10.1190/1.1442209.
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A theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors: fluid and rock conductivities, initial fracture aperture and contact area, fracture surface geometry (asperity height distribution and tip curvature), elastic moduli of the rock, and confining pressure or normal stress acting across the fracture. The conductivity in the fracture plane decreases approximately in proportion to log pressure, but the conductivity is influenced by the increased contact area, and hence flow‐path tortuosity, along the fracture surface at elevated pressures. Electrical conductivity in fractures is more affected by flow‐path tortuosity than is permeability. The dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground, saw‐cut surfaces in a variety of rocks under confining pressures to 200 MPa. The conductivity decreased approximately in proportion to log pressure (there was little effect of increased contact area, and hence tortuosity), which suggests that the contact area may not exceed a few percent of the total apparent area. Measurements of gas permeability through the same split cores showed that when the asperity deformation remained largely elastic, permeability and conductivity had a power of 3 relationship. When asperity collapse occurred, as in a dolomitic marble, the powerlaw relation no longer held; permeability decreased more rapidly under pressure than did conductivity. The different influences of porosity and flow aperture may account for the different behaviors of the two transport properties. The theory suggests a number of ways in which fracture parameters may be extracted from field data. Some of the methods rely on the scale dependence and pressure dependence of the fractured‐rock conductivity; other methods require correlating between different physical properties, such as seismic velocity, which are influenced by the presence of fractures.
12
Zhou, Xin, Jianping Chen, Yunkai Ruan, Wen Zhang, Shengyuan Song, and Jiewei Zhan. "Demarcation of Structural Domains in Fractured Rock Masses Using a Three-Parameter Simultaneous Analysis Method." Advances in Civil Engineering 2018 (December 6, 2018): 1–13. http://dx.doi.org/10.1155/2018/9358098.
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A structural domain represents a volume of a rock mass with similar mechanical and hydrological properties. To demarcate structural domains (or statistically homogeneous regions) in fractured rock masses, this study proposes a three-parameter simultaneous analysis method (3PSAM) that simultaneously considers rock fracture orientation, trace length, and aperture to evaluate statistical homogeneity between two regions. First, a 102-patch three-dimensional Schmidt net, which represents a new comprehensive classification system, is established to characterize rock fractures based on their orientation and aperture. Two populations of rock fractures can then be projected to the corresponding patches. Second, the Wald–Wolfowitz runs test is used to measure the similarity between the two populations by considering the fracture trace lengths. The results obtained by applying the 3PSAM to seven simulated fracture populations show that the homogeneity is influenced by both the distributions of the fracture parameters and the sequences of the fracture parameters. The influence of a specific combination sequence makes it impractical to analyze the rock fracture parameters individually. Combined with previous methods, the 3PSAM provides reasonable and accurate results when it is applied to a fractured rock slope engineering case study in Dalian, China. The results show that each fracture population should be identified as an independent structural domain when using the 3PSAM. Only the 3PSAM identifies the west exploratory trench 2 and the east exploratory trench as being nonhomogeneous because the difference in the aperture of the two fracture populations is considered. The benefit of the 3PSAM is that it simultaneously considers three parameters in the demarcation of structural domains.
13
Dang, Hong-Lam, Duc Phi Do, and Dashnor Hoxha. "Effective Elastic and Hydraulic Properties of Fractured Rock Masses with High Contrast of Permeability: Numerical Calculation by an Embedded Fracture Continuum Approach." Advances in Civil Engineering 2019 (February 3, 2019): 1–21. http://dx.doi.org/10.1155/2019/7560724.
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In this work, the hydromechanical modeling of the fractured rock masses was conducted based on a new numerical simulation method named as embedded fracture continuum (EFC) approach. As the principal advantage, this approach allows to simplify the meshing procedure by using the simple Cartesian meshes to model the fractures that can be explicitly introduced in the porous medium based on the notion of fracture cells. These last elements represent the grid cells intersected by at least one fracture in the medium. Each fracture cell in the EFC approach present a continuum porous medium whose hydromechanical properties are calculated from ones of the matrix and ones of the intersected fractures, thanks for using the well-known solution of the joint model. The determination of the hydromechanical properties of the fracture cells as presented in this work allows to provide the theoretical base and to complete some simple approximations introduced in the literature. Through different verification tests, the capability of the developed EFC approach to model the hydromechanical behavior of fractured rock was highlighted. An analysis of different parameters notably the influence of the fracture cell size on the precision of the proposed approach was also conducted. This novel approach was then applied to investigate the effective permeability and elastic compliance tensor of a fractured rock masses taken from a real field, the Sellafield site. The comparison of the results calculated from this approach with ones conducted in the literature based on the distinct element code (UDEC) presents a good agreement. However, unlike the previous studies using UDEC, which limits only in the case of fractured rock masses without dead-end fractures, our approach allows accounting for this kind of fractures in the medium. The numerical simulations show that the dead-end fractures could have a considerable contribution on the effective compliance moduli, while their effect can be neglected to calculate the overall permeability of the of fractured rock masses.
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Hong-Lam, DANG, and THINH Phi Hong. "A methodology of re-generating a representative element volume of fractured rock mass." Transport and Communications Science Journal 71, no. 4 (May 28, 2020): 347–58. http://dx.doi.org/10.25073/tcsj.71.4.4.
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In simulation of fractured rock mass such as mechanical calculation, hydraulic calculation or coupled hydro-mechanical calculation, the representative element volume of fractured rock mass in the simulating code is very important and give the success of simulation works. The difficulties of how to make a representative element volume are come from the numerous fractures distributed in different orientation, length, location of the actual fracture network. Based on study of fracture characteristics of some fractured sites in the world, the paper presented some main items concerning to the fracture properties. A methodology of re-generating a representative element volume of fractured rock mass by DEAL.II code was presented in this paper. Finally, some applications were introduced to highlight the performance as well as efficiency of this methodology.
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Wang, Xiaolin, Liyuan Yu, and Hanqing Yang. "Correlations between Geometric Properties and Permeability of 2D Fracture Networks." Advances in Civil Engineering 2021 (January 25, 2021): 1–7. http://dx.doi.org/10.1155/2021/6645238.
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The equivalent permeability of fractured rock masses plays an important role in understanding the fluid flow and solute transport properties in underground engineering, yet the effective predictive models have not been proposed. This study established mathematical expressions to link permeability of 2D fracture networks to the geometric properties of fractured rock masses, including number density of fracture lines, total length of fractures per square meter, and fractal dimensions of fracture network structures and intersections. The results show that the equivalent permeability has power law relationships with the geometric properties of fracture networks. The fractal dimensions that can be easily obtained from an engineering site can be used to predict the permeability of a rock fracture network. When the fractal dimensions of fracture network structures and intersections exceed the critical values, the effect of randomness of fracture locations is negligible. The equivalent permeability of a fracture network increases with the increment of fracture density and/or fractal dimensions proportionally.
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Tan, Wenhui, and Pengfei Wang. "Experimental Study on Seepage Properties of Jointed Rock-Like Samples Based on 3D Printing Techniques." Advances in Civil Engineering 2020 (January 21, 2020): 1–10. http://dx.doi.org/10.1155/2020/9403968.
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Sample making of fractured rock mass is a big problem in rock mechanical test. The specimens prepared by traditional rock core drilling have some disadvantages such as unclear internal structure and great difference in mechanical properties; while, the samples prepared by inserting and seaming method have some other disadvantages such as hard to control the attitude of precast-joints, low accuracy. A method for preparing fractured rock-like samples based on 3D printing technology is introduced in this paper, and the seepage characteristics of fractured rock-like samples is studied by seepage experiments. Firstly, the standard profile curves of 10 grades of joint roughness are digitized and 10 groups of 3D digital fracture models are established with different roughness and thickness (i.e., 1.5, 3.0, and 5.0 mm, respectively). 30 fracture inserts are produced by 3D printing technology. Then, rock-like specimens with through-filling fractures are poured with molds. Finally, the permeability tests of the prepared rock-like specimens are carried out to study the seepage characteristics of fractures with different roughness and gap widths under different confining pressures. The results show that 3D printing technology provides an effective way for production of complex crack samples in laboratory test and the comparative analysis of tests. The seepage characteristics of fractures are well studied. When the gap width is small, the permeability decreases with the increase of roughness, and the influence of roughness on fracture permeability decreases rapidly with the increase of confining pressure and gap width. The permeability of through-filling fractures with different roughness and gap width decreases with the increase of confining pressure. The relationship between confining pressure and fracture permeability can be described by the power function. 3D printing technology overcomes the shortcomings of traditional specimen preparation methods and greatly improves the precision of crack inserts. The jointed rock-like model established by the method revealed the influence of fracture characteristics on seepage flow very well.
17
Pang, Shuo, Alexey Stovas, and Huilin Xing. "Frequency-dependent anisotropy in partially saturated porous rock with multiple sets of mesoscale fractures." Geophysical Journal International 227, no. 1 (May 24, 2021): 147–61. http://dx.doi.org/10.1093/gji/ggab204.
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SUMMARY Accurate modelling of the frequency-dependence of seismic wave velocity related to fracture system and fluid content is crucial to the quantitative interpretation of seismic data in fractured reservoirs. Both mesoscale fractures and patchy saturation effects can cause significant velocity dispersion and attenuation in the seismic frequency band due to wave-induced fluid flow (WIFF) mechanism. Considering the coupled impact of ‘mesoscale fractures’ and ‘patchy saturation’, we derive expressions for the frequency-dependent anisotropy in partially saturated porous rock containing two fracture sets with different orientations, sizes and connectivities. Especially, we simplify the rock-physics model as an orthorhombic (ORT) media by assuming the mesoscale fractures to be orthogonal and give the explicit expressions for frequency-dependent elastic constants. Finally, we give the expressions for the frequency-dependent phase velocity in patchy saturated and fractured ORT media and investigate the effect of patchy saturation on P-wave velocity at different polar and azimuth angles. In this paper, we investigate the effects of fluid saturation and fluid pressure on frequency-dependent velocities and Thomsen anisotropy parameters. Also, the effect of the relative permeability is very noticeable. The relaxation frequency can be lower in partially saturated fractured rocks compared with the fully saturated case, which makes the rock have a larger stiffness. The non-monotonic relationships between frequency-dependent anisotropy and fluid saturation add complexity to seismic forward modelling and inversion in reservoirs with complex fracture patterns.
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Cheng, Hua, Xiangyang Liu, Jian Lin, Liangliang Zhang, Mingjing Li, and Chuanxin Rong. "Study on Fracturing and Diffusion Mechanism of Nonslab Fracturing Grouting." Geofluids 2020 (August 12, 2020): 1–9. http://dx.doi.org/10.1155/2020/8838135.
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The coupling effect of a slurry and the fractured rock layer controls a spatial attenuation of the fracture channel width and grouting pressure from a grouting hole to the slurry top of fracture diffusion. This paper comprehensively considers the influencing factors such as the mechanical properties of the injected rock mass and the time-varying characteristics of the serous viscosity and introduces the control equation of the fracture channel width to establish a single-fracture nonslab fracturing grouting model. Combining the motion law of the slurry with the extension form of fracture, the equation of slurry diffusion motion, considering the fracture geometry and the time-varying characteristics of the serous viscosity, is derived. Comparing this equation with the existing theories and experiments, the validity and reliability of the theory are verified. In this paper, the effects of rock elastic modulus, slurry viscosity, and grouting rate on the fracturing grouting diffusion law of rock mass are analyzed. It is pointed out that when fracturing grouting in deep rock layers, a larger initial grouting rate and grouting pressure should be selected in the early stages of grouting to generate or penetrate fractures in the rock layer. Also, when the grouting pressure is stable, it is appropriate to increase the viscosity so that the slurry can quickly gel in the fractures thus sealing the fractures.
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Huang, Zhaoqin, Jun Yao, Yajun Li, Chenchen Wang, and Xinrui Lv. "Numerical Calculation of Equivalent Permeability Tensor for Fractured Vuggy Porous Media Based on Homogenization Theory." Communications in Computational Physics 9, no. 1 (January 2011): 180–204. http://dx.doi.org/10.4208/cicp.150709.130410a.
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AbstractA numerical procedure for the evaluation of equivalent permeability tensor for fractured vuggy porous media is presented. At first we proposed a new conceptual model, i.e., discrete fracture-vug network model, to model the realistic fluid flow in fractured vuggy porous medium on fine scale. This new model consists of three systems: rock matrix system, fractures system, and vugs system. The fractures and vugs are embedded in porous rock, and the isolated vugs could be connected via discrete fracture network. The flow in porous rock and fractures follows Darcy’s law, and the vugs system is free fluid region. Based on two-scale homogenization theory, we obtained an equivalent macroscopic Darcy’s law on coarse scale from fine-scale discrete fracture-vug network model. A finite element numerical formulation for homogenization equations is developed. The method is verified through application to a periodic model problem and then is applied to the calculation of equivalent permeability tensor of porous media with complex fracture-vug networks. The applicability and validity of the method for these more general fractured vuggy systems are assessed through a simple test of the coarse-scale model.
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Strauhal, Thomas, and Christian Zangerl. "The Impact of Fracture Persistence and Intact Rock Bridge Failure on the In Situ Block Area Distribution." Applied Sciences 11, no. 9 (April 27, 2021): 3973. http://dx.doi.org/10.3390/app11093973.
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The in situ block size distribution is an essential characteristic of fractured rock masses and impacts the assessment of rockfall hazards and other fields of rock mechanics. The block size distribution can be estimated rather easily for fully persistent fractures, but it is a challenge to determine this parameter when non-persistent fractures in a rock mass should be considered. In many approaches, the block size distribution is estimated by assuming that the fractures are fully persistent, resulting in an underestimation of the block sizes for many fracture geometries. In addition, the block size distribution is influenced by intact rock bridge failure, especially in rock masses with non-persistent fractures, either in a short-term perspective during a slope failure event when the rock mass increasingly disintegrates or in a long-term view when the rock mass progressively weakens. The quantification of intact rock bridge failure in a rock mass is highly complex, comprising fracture coalescence and crack growth driven by time-dependent changes of the in situ stresses due to thermal, freezing-thawing, and pore water pressure fluctuations. This contribution presents stochastic analyses of the two-dimensional in situ block area distribution and the mean block area of non-persistent fracture networks. The applied 2D discrete fracture network approach takes into account the potential failure of intact rock bridges based on a pre-defined threshold length and relies on input parameters that can be easily measured in the field by classical discontinuity mapping methods (e.g., scanline mapping). In addition, on the basis of these discrete fracture network analyses, an empirical relationship was determined between (i) the mean block area for persistent fractures, (ii) the mean block area for non-persistent fractures, and (iii) the mean interconnectivity factor. The further adaptation of this 2D approach to 3D block geometries is discussed on the basis of general considerations. The calculations carried out in this contribution highlight the large impact of non-persistent fractures and intact rock bridge failure for rock mass characterization, e.g., rockfall assessment.
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Weber, Samuel, Jan Beutel, Jérome Faillettaz, Andreas Hasler, Michael Krautblatter, and Andreas Vieli. "Quantifying irreversible movement in steep, fractured bedrock permafrost on Matterhorn (CH)." Cryosphere 11, no. 1 (February 16, 2017): 567–83. http://dx.doi.org/10.5194/tc-11-567-2017.
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Abstract. Understanding rock slope kinematics in steep, fractured bedrock permafrost is a challenging task. Recent laboratory studies have provided enhanced understanding of rock fatigue and fracturing in cold environments but were not successfully confirmed by field studies. This study presents a unique time series of fracture kinematics, rock temperatures and environmental conditions at 3500 m a. s. l. on the steep, strongly fractured Hörnligrat of the Matterhorn (Swiss Alps). Thanks to 8 years of continuous data, the longer-term evolution of fracture kinematics in permafrost can be analyzed with an unprecedented level of detail. Evidence for common trends in spatiotemporal pattern of fracture kinematics could be found: a partly reversible seasonal movement can be observed at all locations, with variable amplitudes. In the wider context of rock slope stability assessment, we propose separating reversible (elastic) components of fracture kinematics, caused by thermoelastic strains, from the irreversible (plastic) component due to other processes. A regression analysis between temperature and fracture displacement shows that all instrumented fractures exhibit reversible displacements that dominate fracture kinematics in winter. Furthermore, removing this reversible component from the observed displacement enables us to quantify the irreversible component. From this, a new metric – termed index of irreversibility – is proposed to quantify relative irreversibility of fracture kinematics. This new index can identify periods when fracture displacements are dominated by irreversible processes. For many sensors, irreversible enhanced fracture displacement is observed in summer and its initiation coincides with the onset of positive rock temperatures. This likely indicates thawing-related processes, such as meltwater percolation into fractures, as a forcing mechanism for irreversible displacements. For a few instrumented fractures, irreversible displacements were found at the onset of the freezing period, suggesting that cryogenic processes act as a driving factor through increasing ice pressure. The proposed analysis provides a tool for investigating and better understanding processes related to irreversible kinematics.
22
Zheng, Yongxiang, Jianjun Liu, and Yun Lei. "The Propagation Behavior of Hydraulic Fracture in Rock Mass with Cemented Joints." Geofluids 2019 (June 27, 2019): 1–15. http://dx.doi.org/10.1155/2019/5406870.
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The formation of the fracture network in shale hydraulic fracturing is the key to the successful development of shale gas. In order to analyze the mechanism of hydraulic fracturing fracture propagation in cemented fractured formations, a numerical simulation about fracture behavior in cemented joints was conducted based firstly on the block discrete element. And the critical pressure of three fracture propagation modes under the intersection of hydraulic fracturing fracture and closed natural fracture is derived, and the parameter analysis is carried out by univariate analysis and the response surface method (RSM). The results show that at a low intersecting angle, hydraulic fractures will turn and move forward at the same time, forming intersecting fractures. At medium angles, the cracks only turn. At high angles, the crack will expand directly forward without turning. In conclusion, low-angle intersecting fractures are more likely to form complex fracture networks, followed by medium-angle intersecting fractures, and high-angle intersecting fractures have more difficulty in forming fracture networks. The research results have important theoretical guiding significance for the hydraulic fracturing design.
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Ni, Lin, Xue Zhang, Liangchao Zou, and Jinsong Huang. "Phase-field modeling of hydraulic fracture network propagation in poroelastic rocks." Computational Geosciences 24, no. 5 (April 19, 2020): 1767–82. http://dx.doi.org/10.1007/s10596-020-09955-4.
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Abstract Modeling of hydraulic fracturing processes is of great importance in computational geosciences. In this paper, a phase-field model is developed and applied for investigating the hydraulic fracturing propagation in saturated poroelastic rocks with pre-existing fractures. The phase-field model replaces discrete, discontinuous fractures by continuous diffused damage field, and thus is capable of simulating complex cracking phenomena such as crack branching and coalescence. Specifically, hydraulic fracturing propagation in a rock sample of a single pre-existing natural fracture or natural fracture networks is simulated using the proposed model. It is shown that distance between fractures plays a significant role in the determination of propagation direction of hydraulic fracture. While the rock permeability has a limited influence on the final crack topology induced by hydraulic fracturing, it considerably impacts the distribution of the fluid pressure in rocks. The propagation of hydraulic fractures driven by the injected fluid increases the connectivity of the natural fracture networks, which consequently enhances the effective permeability of the rocks.
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FAN, L. F., X. W. YI, and G. W. MA. "NUMERICAL MANIFOLD METHOD (NMM) SIMULATION OF STRESS WAVE PROPAGATION THROUGH FRACTURED ROCK MASS." International Journal of Applied Mechanics 05, no. 02 (June 2013): 1350022. http://dx.doi.org/10.1142/s1758825113500221.
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The present work is devoted to the simulation of stress wave propagation through fractured elastic media, such as rock mass, by using the numerical manifold method (NMM). A single fracture is used to verify the capability and accuracy of the NMM in modeling fractured rock mass. The frequency-dependence on stress wave transmission across a fracture is analyzed. The influence of the fracture specific stiffness on the wave attenuation and effective wave velocity is discussed. The results from the NMM have a good agreement with those obtained from a theoretical displacement discontinuity method (DDM). Taking the advantage that the NMM is able to simulate highly fractured elastic media with a consistent mathematical cover system, a numerical example of stress wave propagation through a fractured rock mass with numerous inherent fractures is presented. It is showed that the results are reasonable and the NMM has a high efficiency in simulating stress wave propagation through highly fractured rock mass. A safety assessment of a tunnel under blast is conducted by using the NMM subsequently. The potential application of the NMM to a more complex fractured rock mass is demonstrated.
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Men, Xiao Xi, C. A. Tang, and Zhi Hui Han. "Numerical Simulation on Propagation Mechanism of Hydraulic Fracture in Fractured Rockmass." Applied Mechanics and Materials 488-489 (January 2014): 417–20. http://dx.doi.org/10.4028/www.scientific.net/amm.488-489.417.
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Hydraulic fracturing process in fractured rockmass which with an existing single natural fracture at its various conditions: its different angles and different lengths was simulated by using RFPA2D(2.0)-Flow version which adopts the finite element method and considers the heterogeneous characteristics of rock in meso-scale, creates seepage-stress-failure coupling model. The effect tendency of natural fractures angle and length on the seepage characteristics of fractured rockmass was given through the description of tensile fracture initiation and propagation in the rock specimens. The simulation results show that the effect of these two factors on fractures initiation, propagation and rockmass stability under the hydraulic fracturing could be remarkable.
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Wu, Yuexiu, Quansheng Liu, Andrew H. C. Chan, and Hongyuan Liu. "Implementation of a Time-Domain Random-Walk Method into a Discrete Element Method to Simulate Nuclide Transport in Fractured Rock Masses." Geofluids 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/5940380.
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It is essential to study nuclide transport with underground water in fractured rock masses in order to evaluate potential radionuclide leakage in nuclear waste disposal. A time-domain random-walk (TDRW) method was firstly implemented into a discrete element method (DEM), that is, UDEC, in this paper to address the pressing challenges of modelling the nuclide transport in fractured rock masses such as massive fractures and coupled hydromechanical effect. The implementation was then validated against analytical solutions for nuclide transport in a single fracture and a simple fracture network. After that, the proposed implementation was applied to model the nuclide transport in a complex fracture network investigated in the DECOVALEX 2011 project to analyze the effect of matrix diffusion and stress on the nuclide transport in the fractured rock masses. It was concluded that the implementation of the TDRW method into UDEC provided a valuable tool to study the nuclide transport in the fractured rock masses. Moreover, it was found that the total travel time of the nuclide particles in the fractured rock masses with the matrix diffusion and external stress modelled was much longer than that without the matrix diffusion and external stress modelled.
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Boadu, Fred K., Joseph Gyamfi, and Emmanuel Owusu. "Determining subsurface fracture characteristics from azimuthal resistivity surveys: A case study at Nsawam, Ghana." GEOPHYSICS 70, no. 5 (September 2005): B35—B42. http://dx.doi.org/10.1190/1.2073888.
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We conducted azimuthal resistivity surveys (ARS) using the square-array configuration to characterize the subsurface fractured rock mass at selected farmland sites in Nsawam District, Ghana. This study is the first of its kind in Ghana, and it provides useful information for future hydrological studies of the area, where groundwater is suspected to be contaminated as a result of the indiscriminate use of pesticides and fertilizers by local farmers. We estimate the fracture orientation, fracture porosity, and coefficient of anisotropy of the fractured rock mass at the selected sites from the azimuthal resistivity measurements; the specific surface area is estimated from field geological mapping of outcrops. High correlations exist between the specific surface area and the real and imaginary parts of the measured resistivity of the fractured rock mass. Fractures at localities with relatively high values of coefficient of anisotropy possess relatively high fracture porosity and relatively low specific surface area and are thus more likely to be intensely fractured and permeable. Results from this integrated geological and geophysical study indicate two dominant fracture directions in the study area, with other minor orientations that may influence groundwater and contaminant transport. The dominant orientations of the fracture systems at Kitase are northwest-southeast in the northern part and northeast-southwest in the southern part. At Amanfrom, the fractures are oriented northwest-southeast, and at Nsakye they are northeast-southwest. These sources of information from a noninvasive geophysical method are useful in assessing the transport properties of the fractured rock mass in the study area.
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Han, Feng Shan, and Li Song. "Numerical Investigation for Fracture Saturation in Multilayer Sedimentary Rock in Unsymmetrical Case." Advanced Materials Research 690-693 (May 2013): 3050–53. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.3050.
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Opening mode fractures in multilayer sedimentary rock often are periodically distributed with fracture spacing scaled to the thickness of the fractured layer. In this paper, based on Rock Failure Process Analysis Code RFPA2D, a three layer model with a central layer and with the different thickness top and bottom layer, progressive formation in multilayer sedimentary rock at fracture saturation in unsymmetrical case is simulated. We investigate the change of the critical fracture spacing to layer thickness ratio as a function of the thickness of the top layer where the bottom layers is much thicker (5 times) than the fractured layer called the unsymmetrical case, in this unsymmetrical case, fracture saturation is simulated. By numerical simulation of RFPA2D, the critical spacing to layer thickness ratio decreases and tend to the same constant value as the thickness of the top layer increases. Numerical simulation shown that for the unsymmetrical case, if the adjacent layers are thicker than 1.5 times the thickness of the fractured layer, the multilayer sedimentary rock can be treated approximately as a system with infinitely thick top and bottom layers at fracture saturation.That should be useful in the design of engineering systems and in the prediction of fracture spacing in hydrocarbon reservoirs and groundwater aquifers.
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Kang, Yong Shui, Quan Sheng Liu, Kai Shi, and Xiao Yan Liu. "Research on Modeling Method for Freezing Tunnel with Fractured Surrounding Rock." Advanced Materials Research 455-456 (January 2012): 1591–95. http://dx.doi.org/10.4028/www.scientific.net/amr.455-456.1591.
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The modeling method for freezing tunnel with fractured surrounding rock is discussed. Frost weathering of rock in cold regions poses serious threat to the stability of geotechnical engineering. Fracture in the freezing rock plays an important role in the mechanical features of the rock mass. However, most of the previous study on freezing rock considered the rock as continuous media, in which the effects of fracture are not reflected sufficiently. This paper overcomes the above-mentioned insufficient and considers the fracture as an important factor while modeling. The model of frost fracture is built by AutoCAD and then transferred into ANSYS for meshing, and finally imported into FLAC3D for calculating by converting procedure. The method of equivalent coefficient of thermal expansion is used to simulate the expansion of water while freezing. The stress and thermal fields after some steps of calculation are ultimately simulated and the influence of fractures is reflected in the results.
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Liu, Yuetian, Zupeng Ding, Kun Ao, Yong Zhang, and Jun Wei. "Manufacturing Method of Large-Scale Fractured Porous Media for Experimental Reservoir Simulation." SPE Journal 18, no. 06 (March 7, 2013): 1081–91. http://dx.doi.org/10.2118/163108-pa.
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Summary A new manufacturing method for a fractured porous model for macroscopic experimental simulation of an oil reservoir is presented to reduce significantly the uncertainty of reservoir numerical simulation. Large numbers of small-cube rocks with the same size made from natural rocks of selected outcrops are bonded in specific ways to form a big rock. The bonded faces among the small rocks compose a 3D fracture system in the big rock. The big rock is the fractured porous medium of the models for experimental reservoir simulation. Every small rock exists as a particle of the fractured medium. Because the number, size, and positions of small rocks can be adjusted optionally, the size and shape of the fractured media can also be adjusted optionally. With the selection of suitable rocks, adhesives, and bonding patterns, the distributions of physical properties in fractured media (e.g., fracture density, permeability, porosity, imbibition) are quantitatively controlled, and they can be heterogeneous and anisotropic in accordance with objective reservoirs. Experimental models made of the fractured media can fully satisfy similarity criteria. The application example in this paper showed that experimental models can be used not only to simulate and forecast directly the exploitation processes of the fractured porous-media reservoirs but also to verify and/or modify numerical reservoir simulation.
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Guo, Ning, Changhong Li, Hao Liu, and Yu Wang. "Dynamic Fracture and Energy Evolution Characterization of Naturally Fractured Granite Subjected to Multilevel Cyclic Loads." Geofluids 2021 (February 20, 2021): 1–16. http://dx.doi.org/10.1155/2021/6685123.
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Naturally fractured rock mass is susceptible to stress disturbance and could result in the stimulation of natural fractures and even serious geological hazards. In this work, multilevel uniaxial fatigue loading experiments were carried out to reveal the fracture and energy evolution of naturally fractured granite using stress-strain descriptions and energy evolution analysis. Results reveal the influence of natural fracture on mechanical properties of granite, regarding the fatigue lifetime, fatigue deformation characteristics, fatigue damage, energy evolution, and fatigue failure pattern. Volumetric and shear processes caused by the sliding and shearing along the natural fracture control the whole failure process. The energy dissipation and release characteristics are strongly impacted by natural fractures. The elastic energy and dissipated energy both decrease with increasing natural fracture volume, growth of the dissipated energy becomes faster for rock near to failure. It is proved that the dissipated energy is mainly used to activate the preexisting natural fractures.
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LIU, RICHENG, BO LI, YUJING JIANG, HONGWEN JING, and LIYUAN YU. "RELATIONSHIP BETWEEN EQUIVALENT PERMEABILITY AND FRACTAL DIMENSION OF DUAL-POROSITY MEDIA SUBJECTED TO FLUID–ROCK REACTION UNDER TRIAXIAL STRESSES." Fractals 26, no. 05 (October 2018): 1850072. http://dx.doi.org/10.1142/s0218348x1850072x.
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Analytical solutions for hydraulic properties of dual-porosity media subjected to fluid–rock reaction under triaxial stresses are derived and the effects of inherent parameters of dual-porosity media and surrounding environments on the relative equivalent permeability are systematically investigated. The results show that the applied triaxial stresses close both fracture aperture and pore diameter, and decrease the equivalent permeabilities of both fractures and rock matrix. The fluid–rock reaction over time decreases the equivalent permeability of fractures, and increases the relative permeability that is the ratio of matrix permeability to fracture permeability. When the time is long, the reaction may be negligible and the relative permeability holds constants. The relative equivalent permeability is more sensitive to the fractal dimension of fracture aperture distribution than that to pore diameter distribution. The relative permeability is significantly influenced by both the maximum fracture aperture and the maximum pore diameter. The rougher fracture surface and the more tortuous capillary correspond to a longer distance that a particle needs to move, thereby resulting in the smaller permeability of fractures and matrix, respectively. In engineering practice, the inherent properties of dual-porosity media can be obtained through geological survey on the outcrops of fractured rock masses and experiments on rock matrix. The triaxial stress can be estimated through ground stress tests. Therefore, it is available to analytically characterize the hydraulic properties of dual-porosity media.
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Men, Xiaoxi, Jiren Li, and Zhihui Han. "Fracture Propagation Behavior of Jointed Rocks in Hydraulic Fracturing." Advances in Materials Science and Engineering 2018 (July 29, 2018): 1–12. http://dx.doi.org/10.1155/2018/9461284.
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Jointed rocks are typical examples of heterogeneous materials with joints. The existence of joints influences the physical properties of rock mass and propagation of fractures, which can affect production operations in engineering. A series of simulations is performed to understand the failure patterns and fracture propagation behavior of jointed rocks in hydraulic fracturing. Three points, that is, dip-angle joint, joint strength, and complex joints, are considered in the simulations. Results demonstrate three basic kinds of hydraulic fractures on jointed rock, namely, along the joint, across the joint, and partly along the joint and partly across the joint. The maximum principal stress is the control factor of fracture propagation in global scale, and the joint plane is the control factor of fracture propagation in local scale. In the propagation path, when the dip angle is small or the joint is weak, the fracture propagates along the joint; otherwise, the fracture propagates across the joint. In the multijoint interconnection models, hydraulic fractures propagate along joints in the tensile stress regions near the propagating fracture tip without dip angle limitation. Subsequently, the fractures connect with one another to form a complex fracture network based on the joint morphology.
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Liu, Jinhui, Yuli Zhou, and Jianguo Chen. "A Two-Dimensional Partitioning of Fracture–Matrix Flow in Fractured Reservoir Rock Using a Dual-Porosity Percolation Model." Energies 14, no. 8 (April 15, 2021): 2209. http://dx.doi.org/10.3390/en14082209.
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Fractures and micropores have varying contributions to the gas permeability of fractured reservoirs. The quantification of the contribution of fractures and micropores that form a dual-porosity system for gas permeability is critical when attempting to accurately evaluate gas production. However, due to insufficient knowledge of fracture–matrix flow partitioning in such dual-porosity systems, it is challenging for previous models to quantitatively characterize the fracture heterogeneity and accurately evaluate the gas flow and permeability in fractured rocks. In this study, we propose a dual-porosity percolation model to quantitatively investigate the contributions of fractures and matrix micropores towards the gas permeability of fractured rocks. Using percolation theory, we establish fracture networks with complex heterogeneity, which are characterized by various fracture densities and percolation probabilities within a porous matrix with various fracture/matrix permeability ratios. The compressible Navier–Stokes and Brinkman equations were adopted to describe the gas flow in the fractures and porous matrix, respectively. The simulation results indicate that the gas permeability of the dual-porosity system has an exponential relationship with the fracture density and matrix permeability. The contribution of fractures and matrix micropores toward gas permeability can be classified by establishing a two-dimensional partitioning of the fracture–matrix flow related to the fracture heterogeneity and fracture/matrix permeability ratio. The contribution of matrix micropores cannot be neglected if the fracture density is lower than a critical value.
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Gong, Lei, Shuai Gao, Xiaofei Fu, Shumin Chen, Bingyang Lyu, and Jiaqi Yao. "Fracture characteristics and their effects on hydrocarbon migration and accumulation in tight volcanic reservoirs: A case study of the Xujiaweizi fault depression, Songliao Basin, China." Interpretation 5, no. 4 (November 30, 2017): SP57—SP70. http://dx.doi.org/10.1190/int-2016-0227.1.
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The Xujiaweizi fault depression is located in the northern part of the Songliao Basin, China. The Yingcheng Formation of the Xujiaweizi fault depression is a fractured tight volcanic reservoir. Many primary pores exist in the tight volcanic reservoirs of the Yingcheng Formation, but their connectivity is very poor. The degree of development of tectonic fractures determines the reservoir quality and the probability of hydrocarbon accumulation. To elucidate the fracture characteristics and their effects on hydrocarbon migration and accumulation, we analyze the fracture genetic types, characteristics, and controlling factors using data from cores, image logs, and thin sections. Then, we evaluate the matching relationship between tectonic fractures and hydrocarbon migration and accumulation by combining the evolution of the source rocks, analysis of the gas-source fault activity period and evolution of the cap rock sealing ability. We find two types of fractures developed in tight volcanic rocks: primary fractures and secondary fractures. Primary fractures mainly include cooling contraction fractures and cryptoexplosive fractures. Secondary fractures could be further divided into tectonic fractures, dissolution fractures, and weathering fractures. Among them, tectonic fractures are dominant. The distribution of tectonic fractures is controlled by lithology, lithofacies, faults, rock anisotropy, and an unconformity. Tectonic fractures are mainly formed in three phases. The time when the second phase of tectonic fractures formed (the Late Quantou-Qingshankou period) coincided with the peak hydrocarbon generation of the source rocks of the Shahezi Formation. Also at that time, the gas-source faults were active and the cap rock had a good top-seal capacity. Thus, the Late Quantou-Qingshankou period was the main period of natural gas accumulation.
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Partsinevelou, Aikaterini-Sofia. "Using the SWAT model in analyzing hard rock hydrogeological environments. Application in Naxos Island, Greece." Bulletin of the Geological Society of Greece 51 (October 4, 2017): 18. http://dx.doi.org/10.12681/bgsg.11960.
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The main parameter that controls the groundwater flow regime in fractured aquifers is the fracture pattern. Its description is crucial for a hydrogeological study, as the hydraulic properties of hard rocks are mainly controlled by fracturing. The parameters of the fracture pattern that were analyzed in the study area were the frequency and spatial location of the fractures, the density of fractures and the degree of fracture intersection.Furthermore, a straight link between the fracture pattern and the hydrological conditions is important for a first analysis of the potential groundwater zones and their vulnerability in hard rock environments. To study this link, the SWAT hydrology model was applied in the study area. Using suitable territorial and meteorological data, the model simulates the parameters of the hydrological balance in each catchment of the hydrographical network.The analysis of the fracture pattern revealed that the fragmentation in all lithologies is characterized by high degree of uniformity. Very high density and interconnection density of the fractures are observed in areas where the alternations between different lithologies are very intense. Also the application of the SWAT model showed that the calculated hydrological parameters could be related to the fracture pattern, as high infiltration rates occur in areas where the density and the degree of interconnection of the fractures are also high.
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Liu, Xiaoli, Tao Liang, Sijing Wang, and Kumar Nawnit. "A Fractal Model for Characterizing Hydraulic Properties of Fractured Rock Mass under Mining Influence." Geofluids 2019 (December 20, 2019): 1–17. http://dx.doi.org/10.1155/2019/8391803.
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In this paper, two basic assumptions are introduced: (1) The number and length distribution of fractures in fractured rock mass are in accordance with the fractal law. (2) Fluid seepage in the fractures satisfies the cubic law. Based on these two assumptions, the fractal model of parallel seepage and radial seepage in fractured rock mass is established, and the seepage tensor of fracture network which reflects the geometric characteristics and fractal characteristics of fracture network under two kinds of seepage is derived. The influence of fracture geometry and fractal characteristics on permeability is analyzed, and the validity and accuracy of the model are verified by comparing the calculated results of the theoretical model and physical model test. The results show that the permeability coefficient K of fracture network is a function of the geometric (maximum crack length Lmax, fractured horizontal projection length L0, diameter calculation section porosity Φ, fracture strike α, and fracture angle θ) and fractal characteristics (fracture network fractal dimension Df and seepage flow fractal dimension DT). With the increase of fractal dimension Df, the permeability coefficient increases. With the increase of DT, the permeability coefficient decreases rapidly. And the larger the Df (Df>1.5), the greater the change of permeability coefficient K with DT.
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Grechka, Vladimir, and Mark Kachanov. "Effective elasticity of rocks with closely spaced and intersecting cracks." GEOPHYSICS 71, no. 3 (May 2006): D85—D91. http://dx.doi.org/10.1190/1.2197489.
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The noninteraction approximation (NIA) is the simplest effective media theory that describes the overall elasticity of fractured rocks. If the NIA is used for fracture characterization, its accuracy and the range of applicability must be estimated. We do it by performing a series of 3D finite element simulations of effective elasticity for models that contain several sets of fractures embedded in otherwise isotropic host rock. We intentionally place the cracks close to each other to create strong interactions in their local stress fields. In addition, we allow the cracks to intersect in such a way that they do not break a rock specimen apart. Perhaps surprisingly, we find that fracture interactions and intersections have little influence on the effective elasticity, and the NIA performs well in all cases. While it has a tendency to slightly underestimate the effective stiffnesses, the incurred errors are small; their typical magnitudes are just a few percent in the entire range of the crack densities expected in naturally fractured formations. In our view, this makes the noninteraction approximation the method of choice for fracture characterization.
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Al-Rubaie, Ali, and Hisham Khaled Ben Mahmud. "A numerical investigation on the performance of hydraulic fracturing in naturally fractured gas reservoirs based on stimulated rock volume." Journal of Petroleum Exploration and Production Technology 10, no. 8 (August 17, 2020): 3333–45. http://dx.doi.org/10.1007/s13202-020-00980-8.
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Abstract All reservoirs are fractured to some degree. Depending on the density, dimension, orientation and the cementation of natural fractures and the location where the hydraulic fracturing is done, preexisting natural fractures can impact hydraulic fracture propagation and the associated flow capacity. Understanding the interactions between hydraulic fracture and natural fractures is crucial in estimating fracture complexity, stimulated reservoir volume, drained reservoir volume and completion efficiency. However, because of the presence of natural fractures with diffuse penetration and different orientations, the operation is complicated in naturally fractured gas reservoirs. For this purpose, two numerical methods are proposed for simulating the hydraulic fracture in a naturally fractured gas reservoir. However, what hydraulic fracture looks like in the subsurface, especially in unconventional reservoirs, remain elusive, and many times, field observations contradict our common beliefs. In this study, the hydraulic fracture model is considered in terms of the state of tensions, on the interaction between the hydraulic fracture and the natural fracture (45°), and the effect of length and height of hydraulic fracture developed and how to distribute induced stress around the well. In order to determine the direction in which the hydraulic fracture is formed strikethrough, the finite difference method and the individual element for numerical solution are used and simulated. The results indicate that the optimum hydraulic fracture time was when the hydraulic fracture is able to connect natural fractures with large streams and connected to the well, and there is a fundamental difference between the tensile and shear opening. The analysis indicates that the growing hydraulic fracture, the tensile and shear stresses applied to the natural fracture.
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Tan, Ran, Junrui Chai, and Cheng Cao. "Experimental Investigation of the Permeability Measurement of Radial Flow through a Single Rough Fracture under Shearing Action." Advances in Civil Engineering 2019 (May 2, 2019): 1–13. http://dx.doi.org/10.1155/2019/6717295.
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Water flow is commonly observed in rock fractures, and this flow has considerable significance in many aspects of rock engineering. In this study, seepage-stress coupled tests were performed on fractured rock masses using a computer-controlled direct shear device for rock with seepage control. The flow direction was radial. Eight types of test case were designed, and subgroup tests with varied normal stress, shear velocity, and roughness of fracture surface were conducted. The failure state of the fracture surface after the shear test, changes in shear stress, and fissure width and permeability under the above conditions were analyzed. The results include the following: the grain size of gouge fragments produced in rough fracture decreased with an increase in normal stress during shearing; the grain size of gouge fragments affected the fracture permeability; and the influence of shear velocity on the test results was mainly reflected after the peak strength. Additionally, a new expression describing fluid flow through fracture gouge is proposed.
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Liu, Xianshan, and Ming Xu. "The Unsaturated Hydromechanical Coupling Model of Rock Slope Considering Rainfall Infiltration Using DDA." Geofluids 2017 (2017): 1–15. http://dx.doi.org/10.1155/2017/1513421.
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Water flow and hydromechanical coupling process in fractured rocks is more different from that in general porous media because of heterogeneous spatial fractures and possible fracture-dominated flow; a saturated-unsaturated hydromechanical coupling model using a discontinuous deformation analysis (DDA) similar to FEM and DEM was employed to analyze water movement in saturated-unsaturated deformed rocks, in which the Van-Genuchten model differently treated the rock and fractures permeable properties to describe the constitutive relationships. The calibrating results for the dam foundation indicated the validation and feasibility of the proposed model and are also in good agreement with the calculations based on DEM still demonstrating its superiority. And then, the rainfall infiltration in a reservoir rock slope was detailedly investigated to describe the water pressure on the fault surface and inside the rocks, displacement, and stress distribution under hydromechanical coupling conditions and uncoupling conditions. It was observed that greater rainfall intensity and longer rainfall time resulted in lower stability of the rock slope, and larger difference was very obvious between the hydromechanical coupling condition and uncoupling condition, demonstrating that rainfall intensity, rainfall time, and hydromechanical coupling effect had great influence on the saturated-unsaturated water flow behavior and mechanical response of the fractured rock slopes.
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Liu, Xiaoqiang, Zhanqing Qu, Tiankui Guo, Ying Sun, Zhifeng Shi, Luyang Chen, and Yunlong Li. "Numerical Simulation of Artificial Fracture Propagation in Shale Gas Reservoirs Based on FPS-Cohesive Finite Element Method." Geofluids 2019 (February 17, 2019): 1–16. http://dx.doi.org/10.1155/2019/9402392.
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The simulation of hydraulic fracturing by the conventional ABAQUS cohesive finite element method requires a preset fracture propagation path, which restricts its application to the hydraulic fracturing simulation of a naturally fractured reservoir under full coupling. Based on the further development of a cohesive finite element, a new dual-attribute element of pore fluid/stress element and cohesive element (PFS-Cohesive) method for a rock matrix is put forward to realize the simulation of an artificial fracture propagating along the arbitrary path. The effect of a single spontaneous fracture, two intersected natural fractures, and multiple intersected spontaneous fractures on the expansion of an artificial fracture is analyzed by this method. Numerical simulation results show that the in situ stress, approaching angle between the artificial fracture and natural fracture, and natural fracture cementation strength have a significant influence on the propagation morphology of the fracture. When two intersected natural fractures exist, the second one will inhibit the propagation of artificial fractures along the small angle of the first natural fractures. Under different in situ stress differences, the length as well as aperture of the hydraulic fracture in a rock matrix increases with the development of cementation superiority of natural fractures. And with the increasing of in situ horizontal stress differences, the length of the artificial fracture in a rock matrix decreases, while the aperture increases. The numerical simulation result of the influence of a single natural fracture on the propagation of an artificial fracture is in agreement with that of the experiment, which proves the accuracy of the PFS-Cohesive FEM for simulating hydraulic fracturing in shale gas reservoirs.
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Man, Ke, Yang Zhao, and He Fei Li. "Coordinate Transformation and the Volume Covering Fractal Algorithm of Rock Surface Morphology." Applied Mechanics and Materials 580-583 (July 2014): 966–70. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.966.
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The mechanics characteristics of the rock are mainly subjected by the joint and the fractures of the rock mass. For the joint, the surface morphology is especially the dominant influence factor. In order to describe the nature physics of rock surface, the surface morphology embarked on a fractured granite rock is described. And use the fractal dimension to calculate the volume of covering rock fracture surface, the relationship between fractal dimension and physical characteristics of rock surface.
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Tang, Qingteng, Wenbing Xie, Xingkai Wang, Zhili Su, and Jinhai Xu. "Numerical Study on Zonal Disintegration of Deep Rock Mass Using Three-Dimensional Bonded Block Model." Advances in Civil Engineering 2019 (October 27, 2019): 1–12. http://dx.doi.org/10.1155/2019/3589417.
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Zonal disintegration, a phenomenon of fractured zones and intact zones distributed alternately in deep rock mass, is different from the excavation-damaged zone of shallow rock mass. In this study, bonded block model of 3DEC was employed to study the fracture mode and origination condition of zonal disintegration. Initiation, propagation, and coalescence progress of fracture around the roadway boundary under different triaxial stress conditions are elaborated. Numerical simulation demonstrated that zonal disintegration may occur when the direction of maximum principal stress is parallel to the roadway axis. It is interesting to find that the fracture around the roadway boundary traced the line of a spiral line, while slip-line fractures distributed apart from the roadway boundary. The extent of the alternate fracture zone decreased as the confining pressure increased, and alternate fracture zone was no longer in existence when the confining pressure reaches a certain value. Effects of roadway shape on zonal disintegration were also studied, and the results indicated that the curvature of the fracture track line tends to be equal to the roadway boundary in shallow surrounding rock of the roadway, while the fractures in deep surrounding rock seems unaffected by the roadway shape. Those findings are of great significance to support design of deep underground openings.
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Gao, Mingzhong, Ting Ai, Zhiqiang Qiu, Zetian Zhang, and Jing Xie. "Analysis of gas migration patterns in fractured coal rocks under actual mining conditions." Thermal Science 21, suppl. 1 (2017): 275–84. http://dx.doi.org/10.2298/tsci17s1275g.
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Fracture fields in coal rocks are the main channels for gas seepage, migration, and extraction. The development, evolution, and spatial distribution of fractures in coal rocks directly affect the permeability of the coal rock as well as gas migration and flow. In this work, the Ji-15-14120 mining face at the No. 8 Coal Mine of Pingdingshan Tian?an Coal Mining Co. Ltd., Pingdingshan, China, was selected as the test site to develop a full-parameter fracture observation instrument and a dynamic fracture observation technique. The acquired video information of fractures in the walls of the boreholes was vectorized and converted to planarly expanded images on a computer-aided design platform. Based on the relative spatial distances between the openings of the boreholes, simultaneous planar images of isolated fractures in the walls of the boreholes along the mining direction were obtained from the boreholes located at various distances from the mining face. Using this information, a 3-D fracture network under mining conditions was established. The gas migration pattern was calculated using a COMSOL computation platform. The results showed that between 10 hours and 1 day the fracture network controlled the gas-flow, rather than the coal seam itself. After one day, the migration of gas was completely controlled by the fractures. The presence of fractures in the overlying rock enables the gas in coal seam to migrate more easily to the surrounding rocks or extraction tunnels situated relatively far away from the coal rock. These conclusions provide an important theoretical basis for gas extraction.
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Chen, Tao. "Equivalent Permeability Distribution for Fractured Porous Rocks: Correlating Fracture Aperture and Length." Geofluids 2020 (October 10, 2020): 1–12. http://dx.doi.org/10.1155/2020/8834666.
Full textAbstract:
Estimating equivalent permeability at grid block scale of numerical models is a critical issue for large-scale fractured porous rocks. However, it is difficult to constrain the permeability distributions for equivalent fracture models as these are strongly influenced by complex fracture properties. This study quantitatively investigated equivalent permeability distributions for fractured porous rocks, considering the impact of the correlated fracture aperture and length model. Two-dimensional discrete fracture models are generated with varied correlation exponent ranges from 0.5 to 1, which indicates different geomechanical properties of fractured porous rock. The equivalent fracture models are built by the multiple boundary upscaling method. Results indicate that the spatial distribution of equivalent permeability varied with the correlation exponent. When the minimum fracture length and the number of fractures increase, the process that the diagonal equivalent permeability tensor components change from a power law like to a lognormal like and to a normal-like distribution slows down as the correlation exponent increases. The average dimensionless equivalent permeability for the equivalent fracture models is well described by an exponential relationship with the correlation exponent. A power law model is built between the equivalent permeability of equivalent fracture models and fracture density of discrete fracture models for the correlated aperture-length models. The results demonstrate that both the fracture density and length-aperture model influence the equivalent permeability of equivalent fracture models interactively.
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Zhang, Lili, Lu Xia, and Qingchun Yu. "Determining the REV for Fracture Rock Mass Based on Seepage Theory." Geofluids 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/4129240.
Full textAbstract:
Seepage problems of the fractured rock mass have always been a heated topic within hydrogeology and engineering geology. The equivalent porous medium model method is the main method in the study of the seepage of the fractured rock mass and its engineering application. The key to the method is to determine a representative elementary volume (REV). The FractureToKarst software, that is, discrete element software, is a main analysis tool in this paper and developed by a number of authors. According to the standard of rock classification established by ISRM, this paper aims to discuss the existence and the size of REV of fractured rock masses with medium tractility and provide a general method to determine the existence of REV. It can be gleaned from the study that the existence condition of fractured rock mass with medium tractility features average fracture spacing smaller than 0.6 m. If average fracture spacing is larger than 0.6 m, there is no existence of REV. The rationality of the model is verified by a case study. The present research provides a method for the simulation of seepage field in fissured rocks.
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Rozov, Konstantin, Vyacheslav Rumynin, Anton Nikulenkov, and Polina Leskova. "Sorption of 137Cs, 90Sr, Se, 99Tc, 152(154)Eu, 239(240)Pu on fractured rocks of the Yeniseysky site (Nizhne-Kansky massif, Russia)." E3S Web of Conferences 98 (2019): 10007. http://dx.doi.org/10.1051/e3sconf/20199810007.
Full textAbstract:
The study demonstrates the effect of sorption properties of fractured host rocks from the Yeniseysky site (Nizhne-Kansky rock massif, Krasnoyarsk region) on the migration of dissolved radioactive components (137Cs, 90Sr, 79Se, 99Tc, 152(154)Eu, 239(240)Pu) in the deep geological conditions of a high-level radioactive waste repository. Estimates of radionuclide distribution coefficients between the aqueous solution and fractured rocks obtained from sorption experiments. The influence of various petrographic types and fracture-filling substances on the retardation of radioactive components has been investigated. Based on the results of sorption experiments, we concluded that the type and attributes of rock discontinuities, as well as the mineral composition of the material in fractures, are crucial for the immobilization of radionuclides during their migration through a geological environment.
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Lemieux, Jean-Michel, Donna Kirkwood, and René Therrien. "Fracture network analysis of the St-Eustache quarry, Quebec, Canada, for groundwater resources management." Canadian Geotechnical Journal 46, no. 7 (July 2009): 828–41. http://dx.doi.org/10.1139/t09-022.
Full textAbstract:
A detailed structural survey has been conducted on a fractured sedimentary rock formation in the St-Eustache quarry, Quebec, Canada, to supplement a hydrogeological study. The two main types of discontinuities in the quarry are horizontal bedding planes and vertical joints. The fracture network is classified as a stratabound network that could be considered as an equivalent porous medium (EPM) for groundwater flow for a volume of rock of 25 to 100 m3. Using detailed statistical data of the fracture network, a geometric model is used to infer a range of hydraulic conductivity values for the low permeability fractures not directly measured with hydraulic tests and treated as EPM for their interpretation. This analysis shows that the vertical and horizontal fractures have about the same permeability in the rock mass, except for a few high hydraulic-conductivity bedding planes. Hydraulic conductivity of single fractures ranges between 1.7 × 10−3 and 1.7 × 10−1 m/s. The porosity of the bulk rock mass inferred from fracture spacing measurements was found to be between 0.03% and 0.3%. Because vertical boreholes provide limited information on vertical fractures, the interpretation of hydraulic tests at the site was greatly improved by the structural surveys.
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Chen, Liang, Shaowu Fan, Can Zhao, Lang Zhang, and Zhiheng Cheng. "Calculation Method of Overburden Damage Height Based on Fracture Mechanics Analysis of Soft and Hard Rock Layers." Geofluids 2019 (February 27, 2019): 1–15. http://dx.doi.org/10.1155/2019/3790264.
Full textAbstract:
Under the geological condition of soft and hard rock interaction stratum, the overburden damage height can provide a quantitative support for the design of the locations of gas drainage boreholes in the roof mining fracture zone and the determination of the hydraulic fracture zone in coal seam mining. The interbedded structure of overlying mud rock and sandstone in the Lu’an mining area in Shanxi is a typical soft and hard rock interaction stratum. In view of the lack of soft rock fracture mechanics analysis and the improper calculation of the damage height of overburden rock caused by constant rock residual bulking coefficient to be used regularly in the analysis, in this paper, we constructed a fracture model of soft and hard strata by giving a quantitative classification criterion of soft and hard rocks and introducing a fracture failure criterion of soft rock strata and the space constraint condition of broken-expansion rock formation. Aiming at improving the calculation precision of overburden damage height, we presented a calculation method based on fracture mechanics analysis of soft and hard strata, which could delineate the extent of intact rock in overlying strata from bottom to top to determine the damage height of overburden rock. This research took Yuwu coal mine in Lu’an mining area as an example. Results showed that (1) by the calculation method, the overburden damage height of the N1102 fully mechanized caving face in Yuwu coal mine was 51.44 m, which was less than the value obtained by an actual borehole TV method as well as the numerical simulation result of 53.46 m, with a calculation accuracy about 96.22%, which is quite high for both. The calculation accuracy of the proposed method was higher than that of the three conventional theoretical methods, and it effectively solved the limitation of the fracture analysis method without the inclusion of the soft rock layer in design and the distortion problem due to the residual bulking coefficient to be improperly used in simulation. (2) There was no noticeable fractures in the broken soft rock zone, and the whole fractures were mainly low-angle rupture; the fractures in hard rock layer had obvious ruptures and multiangle cracks, and the average fracture width of soft rock was 2.8 mm smaller than that of hard rock. The fracture modes of soft rock and hard rock were mainly tensile failure and tensile shear failure, which verified the correctness of the fracture mechanics model of soft and hard rock layers constructed in this paper. (3) It is noticed that the tensile strength of rock in this method needs to be obtained through rock mechanics experiment on overlying strata in the study area, and our proposed method was applicable to the mining conditions of near horizontal coal seam. The calculation accuracy of this method meets the engineering error requirements and can be applied to the prediction of overburden damage height in near horizontal coal seam mining.