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1
Wang, Yueying, Jun Yao, Shuaishi Fu, Aimin Lv, Zhixue Sun e Kelvin Bongole. "Simulation of counter-current imbibition in water-wet fractured reservoirs based on discrete-fracture model". Open Physics 15, n. 1 (3 agosto 2017): 536–43. http://dx.doi.org/10.1515/phys-2017-0061.
Testo completoAbstract (sommario):
AbstractIsolated fractures usually exist in fractured media systems, where the capillary pressure in the fracture is lower than that of the matrix, causing the discrepancy in oil recoveries between fractured and non-fractured porous media. Experiments, analytical solutions and conventional simulation methods based on the continuum model approach are incompetent or insufficient in describing media containing isolated fractures. In this paper, the simulation of the counter-current imbibition in fractured media is based on the discrete-fracture model (DFM). The interlocking or arrangement of matrix and fracture system within the model resembles the traditional discrete fracture network model and the hybrid-mixed-finite-element method is employed to solve the associated equations. The Behbahani experimental data validates our simulation solution for consistency. The simulation results of the fractured media show that the isolated-fractures affect the imbibition in the matrix block. Moreover, the isolated fracture parameters such as fracture length and fracture location influence the trend of the recovery curves. Thus, the counter-current imbibition behavior of media with isolated fractures can be predicted using this method based on the discrete-fracture model.
2
Feng, Yueli, Yuetian Liu e Gang Lei. "Study on Stress-Dependent Permeability of Fracture Networks in Fractured Porous Media". Geofluids 2021 (24 giugno 2021): 1–19. http://dx.doi.org/10.1155/2021/7433547.
Testo completoAbstract (sommario):
In order to investigate the stress-sensitive characteristics of fracture networks under reservoir actual stress condition and its influence on the seepage in fractured porous media, we carried out permeability tests on experimental models with fracture networks under constant-volume boundary condition. In addition, a novel analytical stress-dependent permeability model of fracture networks in different directions was derived. Based on the test results and the proposed analytical model, the effects of various parameters (e.g., initial fracture aperture, fluid pressure, rock elastic modulus, effective-stress coefficient, and fracture dip) on deformation characteristics of fracture networks and the corresponding permeability tensor of fracture networks were studied. The research results show that, for a fractured porous media with a single group of fractures, the principal value of permeability is always parallel to the fracture-development direction. With increasing effective stress, the principal value of permeability decreases; however, the principal value direction remains unchanged. Moreover, for the fractured porous media with multiple sets of fractures, the principal direction of equivalent permeability will be inclined to the fractures with larger fracture aperture. Specifically, for the fractured porous media with two sets of intersecting fractures, the principal direction of equivalent permeability is parallel to the angular bisector of these two sets of intersecting fractures. Furthermore, the greater the difference of the fracture aperture change rate under effective stress, the more obvious the deviation of the permeability principal direction. The derived analytical model is of great theoretical and scientific significance to deepen the understanding of the stress-sensitive permeability of fractured reservoirs.
3
Yuan, Yingzhong, Wende Yan, Fengbo Chen, Jiqiang Li, Qianhua Xiao e Xiaoliang Huang. "Numerical Simulation for Shale Gas Flow in Complex Fracture System of Fractured Horizontal Well". International Journal of Nonlinear Sciences and Numerical Simulation 19, n. 3-4 (26 giugno 2018): 367–77. http://dx.doi.org/10.1515/ijnsns-2017-0135.
Testo completoAbstract (sommario):
AbstractComplex fracture systems including natural fractures and hydraulic fractures exist in shale gas reservoir with fractured horizontal well development. The flow of shale gas is a multi-scale flow process from microscopic nanometer pores to macroscopic large fractures. Due to the complexity of seepage mechanism and fracture parameters, it is difficult to realize fine numerical simulation for fractured horizontal wells in shale gas reservoirs. Mechanisms of adsorption–desorption on the surface of shale pores, slippage and Knudsen diffusion in the nanometer pores, Darcy and non-Darcy seepage in the matrix block and fractures are considered comprehensively in this paper. Through fine description of the complex fracture systems after horizontal well fracturing in shale gas reservoir, the problems of conventional corner point grids which are inflexible, directional, difficult to geometrically discretize arbitrarily oriented fractures are overcome. Discrete fracture network model based on unstructured perpendicular bisection grids is built in the numerical simulation. The results indicate that the discrete fracture network model can accurately describe fracture parameters including length, azimuth and density, and that the influences of fracture parameters on development effect of fractured horizontal well can be finely simulated. Cumulative production rate of shale gas is positively related to fracture half-length, fracture segments and fracture conductivity. When total fracture length is constant, fracturing effect is better if single fracture half-length or penetration ratio is relatively large and fracturing segments are moderate. Research results provide theoretical support for optimal design of fractured horizontal well in shale gas reservoir.
4
Schoenberg, Michael, e Colin M. Sayers. "Seismic anisotropy of fractured rock". GEOPHYSICS 60, n. 1 (gennaio 1995): 204–11. http://dx.doi.org/10.1190/1.1443748.
Testo completoAbstract (sommario):
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.
5
Abedi, Behbood, Mohammad Hossein Ghazanfari e Riyaz Kharrat. "Experimental Study of Polymer Flooding in Fractured Systems Using Five-Spot Glass Micromodel: The Role of Fracture Geometrical Properties". Energy Exploration & Exploitation 30, n. 5 (ottobre 2012): 689–705. http://dx.doi.org/10.1260/0144-5987.30.5.689.
Testo completoAbstract (sommario):
Water flooding is being widely used in the petroleum industry and has been considered as a simple inexpensive secondary recovery method. But in fractured formations, existence of fracture system in reservoir rock induces an adverse effect on oil recovery by water flooding. Polymer flooding has been successfully applied as an alternative enhanced oil recovery method in fractured formations. But, the role of fracture geometrical properties on macroscopic efficiency of polymer flooding is not yet well-understood, especially in fractured five-spot systems. In this work five-spot glass micromodel, because of micro-visibility, ease of multiple experimentations and also presence of the unexplored issues, was used to experimentally investigate the influence of fracture geometrical characteristics such as fracture orientation, fracture spacing, fracture overlap and etc on the macroscopic efficiency of polymer flooding. The tests were performed on the fractured models which are initially saturated with the crude oil at fixed flow rate conditions and in a horizontally mounting. The results revealed that the macroscopic efficiency of polymer flooding depends on fracture geometrical properties. Fracture orientation showed more imposing effect than other fracture geometrical properties, and fracture with 45 degree inclination to the mean flow direction, gives greatest oil recovery factor. Large spacing fractures give more recovery than small spacing ones and in case of overlapping, fractures with less overlapping help polymer to better propagate which could be related to their greater effective fracture length. This pre-called effect could be responsible to show how continuity and width to length ratio of fractures affect recovery factor, less fracture discontinuity as well as more length to width ratio of fracture give more swept zone. Also, increasing number of fractures decreases oil recovery factor. The results of this work can be helpful to better understanding the role of fracture geometrical properties on macroscopic efficiency of polymer flooding in five-spot fractured systems.
6
Shi, Shanzhi, Renyan Zhuo, Leiming Cheng, Yuankai Xiang, Xinfang Ma e Tao Wang. "Fracture Characteristics and Distribution in Slant Core from Conglomerate Hydraulic Fracturing Test Site (CHFTS) in Junggar Basin, Northwest China". Processes 10, n. 8 (19 agosto 2022): 1646. http://dx.doi.org/10.3390/pr10081646.
Testo completoAbstract (sommario):
Hydraulic fracture networks, especially fracture geometry, height growth, and proppant transport within the networks, present a critical influence on productivity evaluation and optimization of fracturing parameters. However, information about hydraulic fracture networks in post-fractured formations is seldom available. In this study, the characteristics (density and orientation) of hydraulic fractures were obtained from field observations of cores taken from conglomerate hydraulic fracturing test site (CHFTS). A large number of fractures were observed in the cores, and systematic fracture description was carried out. The fracture analysis data obtained includes fracture density, fracture depth, fracture orientation, morphology, fracture surface features, apertures, fill, fracture mechanical origin (type), etc. Our results show that 228 hydraulic fractures were intersected in a span of 293.71 m of slant core and composed of irregularly spaced single fractures and fracture swarms. One of the potential sources of the observed fracture swarms is near-wellbore tortuosity. Moreover, for regions far away from the wellbore, reservoir heterogeneity can promote complex hydraulic fracture trajectories. The hydraulic fractures were mainly cross-gravel and high-angle fractures and align with maximum horizontal stress (SHmax) ± 15°. The fracture density, orientations, and types obtained from the core fracture description provided valuable information regarding fracture growth behavior. For the near-wellbore area with a transverse distance of less than 25 m from the hydraulically-fractured wellbore, tensile fractures were dominant. While for the area far away from the wellbore, shear fractures were dominant. Our results provide improved understanding of the spatial hydraulic fracture dimensions, proppant distribution, and mechanism of hydraulic fracture formation. The dataset acquired can also be used to calibrate numerical models and characterize hydraulic fracture geometry and proppant distribution.
7
He, Jiwei, Qin Li, Guodong Jin, Sihai Li, Kunpeng Shi e Huilin Xing. "A Numerical Model for Pressure Analysis of a Well in Unconventional Fractured Reservoirs". Energies 16, n. 5 (6 marzo 2023): 2505. http://dx.doi.org/10.3390/en16052505.
Testo completoAbstract (sommario):
Fractured reservoirs are highly heterogeneous in both matrix and fracture properties, which results in significant variations in well production. Assessing and quantifying the influence of fractures on fluid flow is essential for developing unconventional reservoirs. The complicated effects of fractures in unconventional fractured reservoirs on fluid flow highly depend on fracture geometry, fracture distribution, and fracture properties, which can be reflected in pressure transient testing. The biggest challenge lies in delineating the pre-existing natural fracture distribution pattern, density, azimuth, and connectivity. Using the advanced finite element method, this paper builds a finely characterized near-wellbore model to numerically simulate the pressure transient testing process in naturally fractured reservoirs and further evaluates fracture-related effects to obtain a more accurate solution. First, the numerical program is benchmarked by the analytical solutions and numerical results of Eclipse. Next, different fracture models with single fractures or fracture networks are set up to investigate the effects of fracture parameters numerically (e.g., fracture location, fracture dip angle, fracture spacing, the ratio of fracture permeability to matrix permeability, fracture network orientation, horizontal fracture distribution, etc.) on pressure transient behaviors in naturally fractured reservoirs. Velocity and pressure profiles are presented to visualize and analyze their effects, and new features in the flow regimes of the derivative plots of the bottom-hole pressure are identified and discussed. Finally, based on geological and geophysical data, including image logs, core descriptions, wireline logs, and seismic and well test data, a practical fractured model of the Dalwogan 2 well in the Surat basin is built, analyzed, and compared with homogenous and measured data. The results show significance in characterizing the complex fracture networks in near-wellbore models of unconventional fractured reservoirs.
8
Al-Rubaie, Ali, e 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, n. 8 (17 agosto 2020): 3333–45. http://dx.doi.org/10.1007/s13202-020-00980-8.
Testo completoAbstract (sommario):
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.
9
Liu, Jinhui, Yuli Zhou e Jianguo Chen. "A Two-Dimensional Partitioning of Fracture–Matrix Flow in Fractured Reservoir Rock Using a Dual-Porosity Percolation Model". Energies 14, n. 8 (15 aprile 2021): 2209. http://dx.doi.org/10.3390/en14082209.
Testo completoAbstract (sommario):
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.
10
XU, PENG, HAICHENG LIU, AGUS PULUNG SASMITO, SHUXIA QIU e CUIHONG LI. "EFFECTIVE PERMEABILITY OF FRACTURED POROUS MEDIA WITH FRACTAL DUAL-POROSITY MODEL". Fractals 25, n. 04 (25 luglio 2017): 1740014. http://dx.doi.org/10.1142/s0218348x1740014x.
Testo completoAbstract (sommario):
As natural fractures show statistically fractal scaling laws, fractal geometry has been proposed and applied to model the fracture geometry and to study the hydraulic properties of fractured porous media. In this paper, a fractal dual-porosity model is developed to study the single-phase fluid flow through fractured porous media. An analytical expression for effective permeability of fractured porous media is derived, which depends on the fractal dimension and fracture aperture. The effect of fractal dimensions for fracture aperture distribution and tortuosity, the ratio of minimum to maximum fracture apertures and fracture fraction on the effective permeability have been discussed. In addition, a power law relationship between the effective permeability and fracture fraction is proposed to predict the equivalent hydraulic properties of fractured porous media. Compared with empirical formulas for effective permeability, the present fractal dual-porosity model can capture the statistical characteristics of fractures and shed light on the transport mechanism of fractured porous media.
11
Shi, Di, Liping Li, Jianjun Liu, Mingyang Wu, Yishan Pan e Jupeng Tang. "Effect of discrete fractures with or without roughness on seepage characteristics of fractured rocks". Physics of Fluids 34, n. 7 (luglio 2022): 073611. http://dx.doi.org/10.1063/5.0097025.
Testo completoAbstract (sommario):
This study proposes a new fractal permeability model for fractured rocks that comprehensively accounts for the geometric fracture characteristics and the fluid transport mechanism. Then, the permeability changes of fractured rocks are analyzed using discrete fracture networks (DFNs) with or without roughness and different geometry parameters in the DFN modeling and finite element simulation. The results show that the proposed permeability model well agrees with the experimental data, and the established DFN numerical model more realistically reflects the fracture network in fractured rocks. Fluctuation of tortuous fracture lines (rough fractures) increases the fracture intersection probability, consequently increasing the fracture intersection area or connecting adjacent fractures. Moreover, permeability increases with the fractal dimension Df, porosity ϕ, maximum fracture length lmax, and proportionality coefficient β, and it decreases with increasing fractal dimension DTf of fracture tortuosity. When the fracture proportionality coefficient is 0.001 ≤ β ≤ 0.01, different DFNs yield similar simulation results for permeability. However, with increasing fracture network complexity, the predictive model created using conventional DFN (C-DFN) increasingly overestimates the fractured rock permeability. Thus, building a permeability model for a fractured rock using rough DFN (R-DFN) is more effective than that using C-DFN. Our findings are helpful for real permeability predictions via DFN and analytical modeling.
12
Jiao, Chunyan, Yong Hu, Xuan Xu, Xiaobing Lu, Weijun Shen e Xinhai Hu. "Study on the effects of fracture on permeability with pore-fracture network model". Energy Exploration & Exploitation 36, n. 6 (28 maggio 2018): 1556–65. http://dx.doi.org/10.1177/0144598718777115.
Testo completoAbstract (sommario):
Reservoir quality and productivity of fractured gas reservoirs depend heavily on the degree of fracture development. The fracture evaluation of such reservoir media is the key to quantify reservoir characterization for the purposes such as well drilling and completion as well as development and simulation of fractured gas reservoirs. In this study, a pore-fracture network model was constructed to understand the effects of fracture on permeability in the reservoir media. The microstructure parameters of fractures including fracture length, fracture density, fracture number, and fracture radius were analyzed. Then two modes and effects of matrix and fracture network control were discussed. The results indicate that the network permeability in the fractured reservoir media will increase linearly with fracture length, fracture density, fracture number, and fracture radius. When the fracture radius exceeds 80 µm, the fracture radius has a little effect on network permeability. Within the fracture density less than 0.55, it belongs to the matrix control mode, while the fracture network control mode is dominant in the fracture density exceeding 0.55. The network permeability in the matrix and fracture network control modes is affected by fracture density and the ratio of fracture radius to pore radius. There is a great change in the critical density for the matrix network control compared with the fracture network control. This work can provide a better understanding of the relationship between matrix and fractures, and the effects of fracture on permeability so as to evaluate the fluid flow in the fractured reservoir media.
13
Liu, Hong, Jiang Xin Feng, Ya Long Zhang, Yi Xing Yue, Tao Zhang e Yu Pan. "Mechanism for Network Fracturing in Natural Fractured Reservoir". Advanced Materials Research 868 (dicembre 2013): 718–24. http://dx.doi.org/10.4028/www.scientific.net/amr.868.718.
Testo completoAbstract (sommario):
By the methods of in-house experiment and theory analysis, the fracture initiation, stretch and interconnected mechanism of natural fracture is studied in the fracturing process of main fracture and branch fracture extending. The results have shown that, the hydraulic fracture in fractured formation is composed of a few main fractures in large size and many s secondary fractures in small size. The main fracture has the extending trend with the maximum crustal stress direction. The direction of sub fracture is network along the maximum crustal stress. The higher the degree of natural fractures, the difference between maximum and minimum crustal stress smaller. And the natural fracture is easier to form larger fracture. Fracture orientation and fracture width are determined by different combinations of natural fractures and the relative orientation with the maximum crustal stress.
14
Zhao, Kai, Runsen Li, Haoran Lei, Wei Gao, Zhenwei Zhang, Xiaoyun Wang e Le Qu. "Numerical Simulation of Influencing Factors of Hydraulic Fracture Network Development in Reservoirs with Pre-Existing Fractures". Processes 10, n. 4 (15 aprile 2022): 773. http://dx.doi.org/10.3390/pr10040773.
Testo completoAbstract (sommario):
The intersection behavior of hydraulic fractures and single natural fractures has been studied in detail; however, in fractured reservoirs, natural fractures are numerous and interlaced and the intersection of hydraulic fractures and multiple natural fractures occurs during the fracturing process. This intersection behavior is more complex and there is a lack of research on this topic at present. In this study, a numerical simulation model of the interaction between hydraulic fractures and a series of natural fractures was established, the main factors that affect the formation scale of a fracture network during the hydraulic fracturing of a fractured reservoir were studied using the numerical simulation method, and the parameters were also studied. The results showed that the natural fracture trend, in situ stress difference, and injection flow rate have an impact on the scale of a fracture network. The larger the in situ stress difference, the smaller the scale of the fracture network, which gradually changes from multiple clusters of fractures to single fractures. The larger the injection flow rate, the larger the scale of the fracture network. In the uniform stress field, the direction of a natural fracture is closer to the direction of principal stress, so the lower the fracture extension pressure, the smaller the scale of the network. On the contrary, the farther away from the principal stress direction, the lower the fracture extension pressure and the higher the extension pressure, the larger the scale of the fracture network.
15
Zhang, Qinghe, Bing Zhang, Chen Chen, Ling Li, Xiaorui Wang, Bowen Jiang e Tianle Zheng. "A Test Method for Finding Early Dynamic Fracture of Rock: Using DIC and YOLOv5". Sensors 22, n. 17 (23 agosto 2022): 6320. http://dx.doi.org/10.3390/s22176320.
Testo completoAbstract (sommario):
Intelligent monitoring and early warning of rock mass failure is vital. To realize the early intelligent identification of dynamic fractures in the failure process of complex fractured rocks, 3D printing of the fracture network model was used to produce rock-like specimens containing 20 random joints. An algorithm for the early intelligent identification of dynamic fractures was proposed based on the YOLOv5 deep learning network model and DIC cloud. The results demonstrate an important relationship between the overall strength of the specimen with complex fractures and dynamic fracture propagation, and the overall specimen strength can be judged semi-quantitatively by counting dynamic fracture propagation. Before the initiation of each primary fracture, a strain concentration area appears, which indicates new fracture initiation. The dynamic evolution of primary fractures can be divided into four types: primary fractures, stress concentration areas, new fractures, and cross fractures. The cross fractures have the greatest impact on the overall strength of the specimen. The overall identification accuracy of the four types of fractures identified by the algorithm reached 88%, which shows that the method is fast, accurate, and effective for fracture identification and location, and classification of complex fractured rock masses.
16
Wang, E. Z., Z. Q. Yue, L. G. Tham, Y. Tsui e H. T. Wang. "A dual fracture model to simulate large-scale flow through fractured rocks". Canadian Geotechnical Journal 39, n. 6 (1 dicembre 2002): 1302–12. http://dx.doi.org/10.1139/t02-068.
Testo completoAbstract (sommario):
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.
17
Abdel-Rahman, Hoshang. "Causes and types of complete denture fracture". Zanco Journal of Medical Sciences 15, n. 3 (1 dicembre 2011): 36–40. http://dx.doi.org/10.15218/zjms.2011.031.
Testo completoAbstract (sommario):
Background and objectives: determine the causes and types of complete denture fractures. Methods: The study was performed in the Hawler medical university, college of Dentistry Department of Prosthodontics. The number of fractured complete denture collected was 290 from patients aged 35-80 years of both genders. The (causes of denture fracture, the type of fracture and the history of previous recurrent fractures) were recorded. Results: : The main cause of denture fracture was poor fitting (40%), followed by poor occlusal relation (21%). Midline fracture was the commonest type of fracture (59%). From the study (51%) of the dentures had previously been repaired once or more. The ratio of lower to upper complete denture fractures was approximately 3:1; most of the fractured dentures (56%) were those of males. Conclusion: The causes of the fracture were divided into material factors and clinical/ technical factors. Denture fractures can be reduced by following prosthodontic principles, analyzing proper fit, eliminating occlusal interferences and using high impact polymers or metal reinforced.
18
Fang, Xinding, Yingcai Zheng e Michael C. Fehler. "Fracture clustering effect on amplitude variation with offset and azimuth analyses". GEOPHYSICS 82, n. 1 (1 gennaio 2017): N13—N25. http://dx.doi.org/10.1190/geo2016-0045.1.
Testo completoAbstract (sommario):
Traditional amplitude variation with offset and azimuth (AVOAz) analysis for fracture characterization extracts fracture properties through analysis of reflection AVOAz to determine anisotropic parameters (e.g., Thomsen’s parameters) that are then related to fracture properties. The validity of this method relies on the basic assumption that a fractured unit can be viewed as an equivalent anisotropic medium. As a rule of thumb, this assumption is taken to be valid when the fracture spacing is less than [Formula: see text]. Under the effective medium assumption, diffractions from individual fractures destructively interfere and only specular reflections from boundaries of a fractured layer can be observed in seismic data. The effective medium theory has been widely used in fracture characterization, and its applicability has been validated through many field applications. However, through numerical simulations, we find that diffractions from fracture clusters can significantly distort the AVOAz signatures when a fracture system has irregular spacing even though the average fracture spacing is much smaller than a wavelength (e.g., [Formula: see text]). Contamination by diffractions from irregularly spaced fractures on reflections can substantially bias the fracture properties estimated from AVOAz analysis and may possibly lead to incorrect estimates of fracture properties. Additionally, through Monte Carlo simulations, we find that fracture spacing uncertainty inverted from amplitude variation with offset (AVO) analysis can be up to 10%–20% when fractures are not uniformly distributed, which should be the realistic state of fractures present in the earth. Also, AVOAz and AVO analysis gives more reliable estimates of fracture properties when reflections at the top of the fractured layer are used compared with those from the bottom of the layer.
19
Xue, Jiao, Hanming Gu e Chengguo Cai. "Model-based amplitude versus offset and azimuth inversion for estimating fracture parameters and fluid content". GEOPHYSICS 82, n. 2 (1 marzo 2017): M1—M17. http://dx.doi.org/10.1190/geo2016-0196.1.
Testo completoAbstract (sommario):
The normal-to-shear fracture compliance ratio is commonly used as a fluid indicator. In the seismic frequency range, the fluid indicator lies between the values for isolated fluid-filled fractures and dry fractures, and it is not easy to discriminate the fluid content. Assuming that the fracture surfaces are smooth, we use [Formula: see text], with [Formula: see text] and [Formula: see text] representing the normal fracture weakness of the saturated and dry rock, to indicate fluid types, and to define a fluid influencing factor. The fluid influencing factor is sensitive to the fluid properties, the aspect ratio of the fractures, and the frequency. Conventionally, the amplitude versus offset and azimuth (AVOA) inversion is formulated in terms of the contrasts of the fracture weaknesses across the interface, assuming that the fractures are vertical with the same symmetry axis. We consider fractures with arbitrary azimuths, and develop a method to estimate fracture parameters from wide-azimuth seismic data. The proposed AVOA inversion algorithm is tested on real 3D prestack seismic data from the Tarim Basin, China, and the inverted fracture density show good agreement with well log data, except that there are some discrepancies for one of the fractured reservoir sections. The discrepancies can be ascribed to neglect of the dip angle for the tilted fractures and the conjugate fracture sets, and to the validity of the linear-slip model. The fractured reservoirs are expected to be liquid saturated, under the assumption of smooth fractures. Overall, the inverted fracture density and fluid influencing factor can be potentially used for better well planning in fractured reservoirs and quantitatively estimating the fluid effects.
20
Chen, Zhiming, Xinwei Liao, Kamy Sepehrnoori e Wei Yu. "A Semianalytical Model for Pressure-Transient Analysis of Fractured Wells in Unconventional Plays With Arbitrarily Distributed Discrete Fractures". SPE Journal 23, n. 06 (7 settembre 2018): 2041–59. http://dx.doi.org/10.2118/187290-pa.
Testo completoAbstract (sommario):
Summary In this paper, we present an efficient semianalytical model for pressure-transient analysis in fractured wells by considering arbitrarily distributed fracture networks. The semianalytical model included three domains: matrix, hydraulic-fracture networks, and discrete natural fractures. Using the line-source function, we developed the diffusivity equation for fluid flow in matrix. By applying the vertex-analysis technique, we eliminated the flow interplay at fracture intersections and established the diffusivity equations for fluid flow in hydraulic-fracture networks and isolated natural fractures. The pressure-transient solution of these diffusivity equations was obtained using Laplace transforms and the Stehfest numerical inversion. Results showed that with the discrete natural fractures, a “V-shaped” pressure derivative (the classical dual-porosity feature of naturally fractured reservoirs) emerged. With the hydraulic-fracture networks, the reservoir system would exhibit pressure behaviors such as “pseudoboundary-dominated flow,” “fracture-interference flow,” and “fluid-feed flow.” All these pressure characteristics were dependent on the properties and geometries of natural/hydraulic fractures. In addition, through synthetic field application, we found that different (natural/hydraulic) fracture distributions and geometries had distinct behaviors of pressure derivatives, which may provide an effective tool to identify the properties of randomly distributed natural fractures as well as complex hydraulic fractures in unconventional plays.
21
Iftikhar, Javeria, Muhammad Nasir Saleem, Faiza Awais, Ayesha Naz, Adeel Tuasene, Zain Saleem e Khezran Qamar. "Frequency and Causes of Fracture of Acrylic Resin Complete Dentures in Edentulous patients". Pakistan Journal of Medical and Health Sciences 16, n. 7 (30 luglio 2022): 160–62. http://dx.doi.org/10.53350/pjmhs22167160.
Testo completoAbstract (sommario):
Background: The rehabilitation of edentulous patients requires acrylic resin complete dentures to fulfil their functional and esthetic needs. Fractures of dentures are one of the commonest complaints around the world. Aim: To evaluate the frequency of acrylic complete denture fractures among edentulous patients and find out their association with certain variables. Methodology: A cross sectional observational study was carried out in Prosthodontic department of Lahore Medical and Dental College, Lahore from 26th March 2020 to 26th September 2021. A total of 58 completely edentulous patients reported with fractured acrylic dentures were selected. Patients were evaluated both intra and extra orally to find out the cause and site of fracture. Various parameters namely, denture age, fracture sites, gender were statistically evaluated to find out their relationship with denture fracture. Results: Results showed that male patients; 56.9% were presenting more with fractured dentures than female; 43.10%. In males the midline denture fractures were most commonly seen 45.5%, whereas in females’ fracture at premolar area was commonly observed 28.0% however no statistical dependance between fractured dentures sites and gender was found. Denture fractures were most prevalent in mandibular arch 50% as compared to maxillary 39.7%. Mid line fracture was the commonest site observed in both maxillary 30.4% and mandibular arches 31.0%. Insignificant association between fracture sites and dental arches was seen. Maximum denture fractures were recorded in first 2 years of denture fabrication 55.2%. The most frequent cause of denture fracture was accidental falling 34.5%. Conclusion: The frequency of complete denture fracture is more in mandible as compared to maxilla and the main reason is patients’ negligence. The study also showed midline fracture of dentures to be the most frequent site of denture fracture. Keywords: Acrylic dentures, Complete dentures, Edentulism, Edentulous, Prosthesis, Tooth loss,
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Li, Liyong, e Seong H. Lee. "Efficient Field-Scale Simulation of Black Oil in a Naturally Fractured Reservoir Through Discrete Fracture Networks and Homogenized Media". SPE Reservoir Evaluation & Engineering 11, n. 04 (1 agosto 2008): 750–58. http://dx.doi.org/10.2118/103901-pa.
Testo completoAbstract (sommario):
Summary This paper describes a hybrid finite volume method, designed to simulate multiphase flow in a field-scale naturally fractured reservoir. Lee et al. (WRR 37:443-455, 2001) developed a hierarchical approach in which the permeability contribution from short fractures is derived in an analytical expression that from medium fractures is numerically solved using a boundary element method. The long fractures are modeled explicitly as major fluid conduits. Reservoirs with well-developed natural fractures include many complex fracture networks that cannot be easily modeled by simple long fracture formulation and/or homogenized single continuity model. We thus propose a numerically efficient hybrid method in which small and medium fractures are modeled by effective permeability, and large fractures are modeled by discrete fracture networks. A simple, systematic way is devised to calculate transport parameters between fracture networks and discretized, homogenized media. An efficient numerical algorithm is also devised to solve the dual system of fracture network and finite volume grid. Black oil formulation is implemented in the simulator to demonstrate practical applications of this hybrid finite volume method. Introduction Many reservoirs are highly fractured due to the complex tectonic movement and sedimentation process the formation has experienced. The permeability of a fracture is usually much larger than that of the rock matrix; as a result, the fluid will flow mostly through the fracture network, if the fractures are connected. This implies that the fracture connectivities and their distribution will determine fluid transport in a naturally fractured reservoir (Long and Witherspoon 1985). Because of statistically complex distribution of geological heterogeneity and multiple length and time scales in natural porous media, three approaches (Smith and Schwartz 1993) are commonly used in describing fluid flow and solute transport in naturally fractured formations:discrete fracture models;continuum models using effective properties for discrete grids; andhybrid models that combine discrete, large features and equivalent continuum. Currently, most reservoir simulators use dual continuum formulations (i.e., dual porosity/permeability) for naturally fractured reservoirs in which matrix blocks are divided by very regular fracture patterns (Kazemi et al. 1976, Van Golf-Racht 1982). Part of the primary input into these simulation models is the permeability of the fracture system assigned to the individual grid-blocks. This value can only be reasonably calculated if the fracture systems are regular and well connected. Field characterization studies have shown, however, that fracture systems are very irregular, often disconnected, and occur in swarms (Laubach 1991, Lorenz and Hill 1991, Narr et al. 2003). Most naturally fractured reservoirs include fractures of multiple- length scales. The effective grid-block permeability calculated by the boundary element method becomes expensive as the number of fractures increases. The calculated effective properties for grid-blocks also underestimates the properties for long fractures whose length scale is much larger than the grid-block size. Lee et al. (2001) proposed a hierarchical method to model fluid flow in a reservoir with multiple-length scaled fractures. They assumed that short fractures are randomly distributed and contribute to increasing the effective matrix permeability. An asymptotic solution representing the permeability contribution from short fractures was derived. With the short fracture contribution to permeability, the effective matrix permeability can be expressed in a general tensor form. Thus, they also developed a boundary element method for Darcy's equation with tensor permeability. For medium-length fractures in a grid-block, a coupled system of Poisson equations with tensor permeability was solved numerically using a boundary element method. The grid-block effective permeabilities were used with a finite difference simulator to compute flow through the fracture system. The simulator was enhanced to use a control-volume finite difference formulation (Lee et al. 1998, 2002) for general tensor permeability input (i.e., 9-point stencil for 2-D and 27-point stencil for 3-D). In addition, long fractures were explicitly modeled by using the transport index between fracture and matrix in a gridblock. In this paper we adopt their transport index concept and extend the hierarchical method:to include networks of long fractures;to model fracture as a two-dimensional plane; andto allow fractures to intersect with well bore. This generalization allows us to model a more realistic and complex fracture network that can be found in naturally fractured reservoirs. To demonstrate this new method for practical reservoir applications, we furthermore implement a black oil formulation in the simulator. We explicitly model long fractures as a two-dimensional plane that can penetrate several layers. The method, presented in this paper, allows a general description of fracture orientation in space. For simplicity of computational implementation however, both the medium-length and long fractures considered in this paper are assumed to be perpendicular to bedding boundaries. In addition, we derive a source/sink term to model the flux between matrix and long fracture networks. This source/sink allows for coupling multiphase flow equations in long fractures and matrix. The paper is organized as follows. In Section 2 black oil formulation is briefly summarized and the transport equations for three phase flow are presented. The fracture characterization and hierarchical modeling approach, based on fracture length, are discussed in Section 3. In Section 4 we review homogenization of short and medium fractures, which is part of our hierarchical approach to modeling flow in porous media with multiple length-scale fractures. In Section 5 we discuss a discrete network model of long fractures. We also derive transfer indices between fracture and effective matrix blocks. In Section 6 we present numerical examples for tracer transport in a model with simple fracture network, interactions of fractures and wells, and black oil production in a reservoir with a complex fracture network system. Finally, the summary of our main results and conclusion follows.
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Li, Jianxiong, Shiming Dong, Wen Hua, Xiaolong Li e Xin Pan. "Numerical Investigation of Hydraulic Fracture Propagation Based on Cohesive Zone Model in Naturally Fractured Formations". Processes 7, n. 1 (8 gennaio 2019): 28. http://dx.doi.org/10.3390/pr7010028.
Testo completoAbstract (sommario):
Complex propagation patterns of hydraulic fractures often play important roles in naturally fractured formations due to complex mechanisms. Therefore, understanding propagation patterns and the geometry of fractures is essential for hydraulic fracturing design. In this work, a seepage–stress–damage coupled model based on the finite pore pressure cohesive zone (PPCZ) method was developed to investigate hydraulic fracture propagation behavior in a naturally fractured reservoir. Compared with the traditional finite element method, the coupled model with global insertion cohesive elements realizes arbitrary propagation of fluid-driven fractures. Numerical simulations of multiple-cluster hydraulic fracturing were carried out to investigate the sensitivities of a multitude of parameters. The results reveal that stress interference from multiple-clusters is responsible for serious suppression and diversion of the fracture network. A lower stress difference benefits the fracture network and helps open natural fractures. By comparing the mechanism of fluid injection, the maximal fracture network can be achieved with various injection rates and viscosities at different fracturing stages. Cluster parameters, including the number of clusters and their spacing, were optimal, satisfying the requirement of creating a large fracture network. These results offer new insights into the propagation pattern of fluid driven fractures and should act as a guide for multiple-cluster hydraulic fracturing, which can help increase the hydraulic fracture volume in naturally fractured reservoirs.
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Zhang, Hai Yong, Shun Li He, Guo Hua Luan, Qiao Lu, Shao Yuan Mo, Zhang Zhang e Gang Lei. "Influence of Fracture Parameters on the Productivity of Fractured Horizontal Well Based on Fluid Mechanics in Tight Gas Reservoir". Advanced Materials Research 886 (gennaio 2014): 452–55. http://dx.doi.org/10.4028/www.scientific.net/amr.886.452.
Testo completoAbstract (sommario):
Multiple fractures are needed by hydraulic fracturing in order to improve the horizontal well productivity of a single well in tight gas reservoir. The calculation accuracy of productivity influences on the fracturing optimization results and the success ratio and effectiveness of fracturing treatment. This work focuses on analyzing the influence of fracture parameters on fractured horizontal well productivity in tight gas reservoir through establishing a productivity prediction model of fractured horizontal well, considering the interference between fracture and fracture and the wellbore pressure drop. Results show that the fracture parameters, such as fracture number, fracture interval, fracture conductivity and fracture length, have different influences on the productivity of fractured horizontal well and thus, the effects of fracture parameters should be taken into account when designing the fracturing treatment.
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Xu, Chaoshui, Shaoqun Dong, Hang Wang, Zhihe Wang, Feng Xiong, Qinghui Jiang, Lianbo Zeng, Leon Faulkner, Zhao Feng Tian e Peter Dowd. "Modelling of Coupled Hydro-Thermo-Chemical Fluid Flow through Rock Fracture Networks and Its Applications". Geosciences 11, n. 4 (29 marzo 2021): 153. http://dx.doi.org/10.3390/geosciences11040153.
Testo completoAbstract (sommario):
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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Zheng, Hanwen, Zhansong Zhang, Jianhong Guo, Sinan Fang e Can Wang. "Numerical Simulation Study on the Influence of Cracks in a Full-Size Core on the Resistivity Measurement Response". Energies 17, n. 6 (13 marzo 2024): 1386. http://dx.doi.org/10.3390/en17061386.
Testo completoAbstract (sommario):
The development of fractured oil fields poses a formidable challenge due to the intricate nature of fracture development and distribution. Fractures profoundly impact core resistivity, making it crucial to investigate the mechanism behind the resistivity response change in fracture cores. In this study, we employed the theory of a stable current field to perform a numerical simulation of the resistivity response of single-fracture and complex-fracture granite cores, using a full-size granite core with cracks as the model. We considered multiple parameters of the fracture itself and the formation to explore the resistivity response change mechanism of the fracture core. Our findings indicate that, in the case of a core with a single fracture, the angle, width, and length of the fracture (fracture occurrence) significantly affect core resistivity. When two fractures run parallel for a core with complex fractures, the change law of core resistivity is similar to that of a single fracture. However, if two fractures intersect, the relative position of the two fractures becomes a significant factor in addition to the width and length of the fracture. Interestingly, a 90° difference exists between the change law of core resistivity and the change law of the resistivity logging response. Furthermore, the core resistivity is affected by matrix resistivity and the resistivity of the mud filtrate, which emphasizes the need to calibrate the fracture dip angle calculated using dual laterolog resistivity with actual core data or special logging data in reservoirs with different geological backgrounds. In the face of multiple fractures, the dual laterolog method has multiple solutions. Our work provides a reference and theoretical basis for interpreting oil and gas in fractured reservoirs based on logging data and holds significant engineering guiding significance.
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Al Nefaie, Hamed, Zuhair Alsuhaymi, Ahmed Alzahrani, Abdulaziz Alghamdi, Emtenan Esmael, Nuran Eid, Eyad Agheel et al. "Fracture Patterns in Saudi Arabian Road Traffic Accidents Over the Last 12 Years: A Systematic Review". Journal of Healthcare Sciences 02, n. 11 (2022): 413–21. http://dx.doi.org/10.52533/johs.2022.21113.
Testo completoAbstract (sommario):
Background: Road traffic accidents are a major non-communicable epidemic that accounts for death and morbidity in the world today. Despite considerable attention given to health statistics of road traffic accidents (RTAs), the pattern of bone fracture aspects of injuries resulting from RTAs is not fully understood in Saudi Arabia. This review aimed to study the epidemiological pattern of fractures due to RTAs in Saudi Arabia. Methods: This systematic review was based on the latest evidence of RTA fractures in the Kingdom of Saudi Arabia (SAUDI ARABIA). All articles published during the last 12 years on road traffic accident-associated fractures in SAUDI ARABIA were analyzed. We examined 12 studies published between 2012 and 2022. Eleven included studies were cross-sectional studies and collected data retrospectively, while one study was a cohort. Results: A total of 4709 patients with fractures admitted in 2010–2022, followed by road traffic accidents, were included. Male patients accounted for 81.6% (n = 3843) of all fractures reported. The most commonly fractured body areas were the upper limb extremities (30.05%), followed by lower limb extremities (11.30%), head or skull fracture (10.53%), spine fracture (8.83%), ribs fracture (8.52%), neck fracture (8.09%), pelvis fracture (3.44%), clavicle fracture (1.89%), and sternal fracture (0.28%). Among the upper limb fractures, the femur bone was most fractured (17.06%), and the combined tibia patella and fibula accounted for 17.69% of upper limb fractures. Conclusion: Lower limb fractures, especially femur bone fractures, are prevalent in Saudi Arabia, and caused by RTAs, especially among young males. Therefore, the concerned authorities need to employ and implement stricter traffic rules to minimize the risk of RTA fractures and their subsequent increased morbidity and mortality rates
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Ren, Qingshan, Yaodong Jiang, Pengpeng Wang, Guangjie Wu e Nima Noraei Danesh. "Experimental and Numerical Simulation Study of Hydraulic Fracture Propagation during Coalbed Methane Development". Geofluids 2021 (17 agosto 2021): 1–12. http://dx.doi.org/10.1155/2021/3632997.
Testo completoAbstract (sommario):
The extraction of low-permeability coalbed methane (CBM) has the dual significance of energy utilization and safe mining. Understanding hydraulic fracturing mechanism is vital to successful development of CBM. Therefore, it is important to improve the law of hydraulic fracture propagation in coal and rigorously study the influencing factors. In this paper, laboratory experiments and numerical simulation methods were used to investigate the hydraulic fracture propagation law of coal in coalbed methane reservoir with natural fractures. The results show that the maximum and minimum horizontal in situ stress and the difference in stress significantly affect the direction of crack propagation. The elastic modulus of coal, the mechanical properties of natural fractures, and the injection rate can affect the fracture length, fracture width, and the amount of fracturing fluid injected. To ensure the effectiveness of hydraulic fracturing, a reservoir environment with a certain horizontal stress difference under specific reservoir conditions can ensure the increase of fractured reservoir and the controllability of fracture expansion direction. In order to increase the volume of fractured reservoir and fracture length, the pumping speed of fracturing fluid should not be too high. The existence of stress shadow effect causes the hydraulic fracture to propagate along the main fracture track, where the branch fracture cannot extend too far. Complex fractures are the main hydraulic fracture typology in coalbed methane reservoir with natural fractures. The results can provide a benchmark for optimal design of hydraulic fracturing in coalbed methane reservoirs.
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Cai, Ming, Hongliang Wu, Yi Xin, Peng Liu, Chengguang Zhang, Jun Tang, Minjie Lin e Lihong Tan. "Experimental Study on Shear Wave Transmission in Fractured Media". Sensors 22, n. 11 (26 maggio 2022): 4047. http://dx.doi.org/10.3390/s22114047.
Testo completoAbstract (sommario):
Unconventional oil and gas reservoirs have broad exploration and development prospects. Fracture parameters and effectiveness evaluation are two of the key tasks for the evaluation of these types of reservoirs. Array acoustic logging can be used for fracture evaluation to compensate for the deficiencies of the image logging fracture evaluation method. Therefore, to develop acoustic logging evaluation methods as well as nondestructive testing methods for fractures, experiments were conducted to study the shear wave transmission in fractured media. Experiment data demonstrate a good correlation between the shear wave attenuation coefficient and fracture width, and the shear wave attenuation coefficients rise logarithmically with the increase in the fracture width for all models with different porosities and distinct dip angles of fractures. The shear wave attenuation coefficient changes relatively faster with the fracture width when the fracture width is within 250 μm. In addition, the shear wave attenuation is affected by the core porosity and fracture dip angle. When the fracture width is constant, the shear wave attenuation caused by the 0° fracture is relatively larger and is obviously greater than that of the fractures at other angles, which is consistent with the existing experimental results. The results of this study can be used to guide further research on amplitude compensation methods for sonic signal transmission in fractured media and fracture evaluation methods.
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Sarda, S., L. Jeannin, R. Basquet e B. Bourbiaux. "Hydraulic Characterization of Fractured Reservoirs: Simulation on Discrete Fracture Models". SPE Reservoir Evaluation & Engineering 5, n. 02 (1 aprile 2002): 154–62. http://dx.doi.org/10.2118/77300-pa.
Testo completoAbstract (sommario):
Summary Advanced characterization methodology and software are now able to provide realistic pictures of fracture networks. However, these pictures must be validated against dynamic data like flowmeter, well-test, interference-test, or production data and calibrated in terms of hydraulic properties. This calibration and validation step is based on the simulation of those dynamic tests. What has to be overcome is the challenge of both accurately representing large and complex fracture networks and simulating matrix/ fracture exchanges with a minimum number of gridblocks. This paper presents an efficient, patented solution to tackle this problem. First, a method derived from the well-known dual-porosity concept is presented. The approach consists of developing an optimized, explicit representation of the fractured medium and specific treatments of matrix/fracture exchanges and matrix/matrix flows. In this approach, matrix blocks of different volumes and shapes are associated with each fracture cell depending on the local geometry of the surrounding fractures. The matrix-block geometry is determined with a rapid image-processing algorithm. The great advantage of this approach is that it can simulate local matrix/fracture exchanges on large fractured media in a much faster and more appropriate way. Indeed, the simulation can be carried out with a much smaller number of cells compared to a fully explicit discretization of both matrix and fracture media. The proposed approach presents other advantages owing to its great flexibility. Indeed, it accurately handles the cases in which flows are not controlled by fractures alone; either the fracture network may be not hydraulically connected from one well to another, or the matrix may have a high permeability in some places. Finally, well-test cases demonstrate the reliability of the method and its range of application. Introduction In recent years, numerous research programs have been focusing on the topic of fractured reservoirs. Major advances were made, and oil companies now benefit from efficient methodologies, tools, and software for fractured reservoir studies. Nowadays, a study of a fractured reservoir, from fracture detection to full-field simulation, includes the following main steps: geological fracture characterization, hydraulic characterization of fractures, upscaling of fracture properties, and fractured reservoir simulation. Research on fractured reservoir simulation has a long history. In the early 1960s, Barenblatt and Zheltov1 first introduced the dual-porosity concept, followed by Warren and Root,2 who proposed a simplified representation of fracture networks to be used in dual-porosity simulators. Based on this concept, reservoir simulators3 are now able to correctly reproduce the main driving mechanisms occurring in fractured reservoirs, such as water imbibition, gas/oil and water/oil gravity drainage, molecular diffusion, and convection in fractures. Even single-medium simulators can perform fractured reservoir simulation when adequate pseudocapillary pressure curves and pseudorelative permeability curves can be input. Indeed, except for particular cases such as thermal recovery processes, full-field simulation of fractured reservoirs is no longer a problem. Geological characterization of fractures progressed considerably in the 1990s. The challenge was to analyze and integrate all the available fracture data to provide a reliable description of the fracture network both at field scale and at local reservoir cell scale. Tools have been developed for merging seismic, borehole imaging, lithological, and outcrop data together with the help of geological and geomechanical rules.3 These tools benefited from the progress of seismic acquisition and borehole imaging. Indeed, accurate seismic data lead to reliable models of large-scale fracture networks, and borehole imaging gives the actual fracture description along the wells, which enables a reliable statistical determination of fracture attributes. Finally, these tools provide realistic pictures of fracture networks. They are applied successfully in numerous fractured-reservoir studies. The upscaling of fracture properties is the problem of translating the geological description of fracture networks into reservoir simulation parameters. Two approaches are possible. In the first one, the fractured reservoir is considered as a very heterogeneous matrix reservoir; therefore, one applies the classical techniques available for heterogeneous single-medium upscaling. The second approach is based on the dual-porosity concept and consists of upscaling the matrix and the fracture separately. Based on this second approach, methodologies and software were developed in the 1990s to calculate equivalent fracture parameters with respect to the dual-porosity concept (i.e., a fracture-permeability tensor with main flow directions and anisotropy and a shape factor that controls the matrix/fracture exchange kinetics3–5). For a given reservoir grid cell, the upscaling procedures consist of generating the corresponding 3D discrete fracture network and computing the equivalent parameters from this network. In particular, the permeability tensor is computed from the results of steady-state flow simulations in the discrete fracture network alone (without the matrix).
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Khurshid, Ilyas, Emad Walid AlShalabi, Hazim Al-Attar e Ahmed Khalifa AL-Neaimi. "Analysis of formation damage and fracture choking in hydraulically induced fractured reservoirs due to asphaltene deposition". Journal of Petroleum Exploration and Production Technology 10, n. 8 (22 maggio 2020): 3377–87. http://dx.doi.org/10.1007/s13202-020-00910-8.
Testo completoAbstract (sommario):
Abstract Hydraulically induced fractures provide a significant fraction of oil supply to the world from unconventional reservoirs due to their high permeability. However, these fractures might choke because of the deposition of organic and in-organic particles. Among organic particles, asphaltene deposition severely reduces reservoir permeability causing an exponential drop in production. In this work, a simulator is developed that predicts the performance of fractured reservoirs by solving the fluid flow governing equations for matrix and fractures. These flow equations were then incorporated with asphaltene deposition equations. Primarily, a numerical model is developed to predict the rate of asphaltene deposition and fracture choking in a radial geometry. It is found that asphaltene deposition could partially or completely choke fractures. Finally, the results are compared with the experimental data and determined various factors affecting fracture choking. From the detailed analysis, it is found that fracture choking is a few percent, but it increases with long production time. The sensitivity analysis was performed to investigate the effect of different influential parameters on permeability alteration of fractured reservoirs by asphaltene deposition. These parameters include fracture-to-matrix permeability ratio, production time, and asphaltene concentration. It is observed that, low fracture-to-matrix permeability ratio has a negligible effect on permeability of a reservoir. The developed model assumes negligible gravity and capillary forces. However, these forces might increase fracture choking in unconventional fractured reservoirs.
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Yu, Qingyan, Qi Wang, Pengcheng Liu, Jing Zhang, Qi Zhang, Xiaojuan Deng e Kai Feng. "Theoretical Study and Application of Rate Transient Analysis on Complex Fractured-Caved Carbonate Reservoirs". Geofluids 2021 (23 gennaio 2021): 1–15. http://dx.doi.org/10.1155/2021/6611957.
Testo completoAbstract (sommario):
Carbonate reservoirs are mainly fractured-caved reservoirs with very well-developed dissolved pores, fractures, and caves. They have strong heterogeneity with various types of reservoir pore spaces. Using seismic inversion and reservoir static characterization, the result shows that the fractured-caved carbonate rocks in China are mainly caves with poor connectivity and complex oil-water distribution. Large-scale dissolved caves are mostly discrete and isolated, while the fractures are complex and various. The fracture features are observed either as a single large fractures or as a local fracture network. The characteristics of fluid flow in fracture-caved reservoirs vary as a result of the different combinations of fractures and caves. Currently, the static characterization technology of fractured-caved reservoirs is influenced by the limited resolution of seismic data, leading to large interpretation errors. In contrast, the dynamic method is a more reliable and effective method to determine reservoir parameters. However, traditional seepage equations cannot accurately characterize the flow pattern of fractured-caved carbonate reservoirs. In the case of a single large-scale dissolved fractured-caved reservoir, oil wells are usually connected to large caves through large fractures or directly drilled into large dissolved caves. In this study, the large-scale dissolved caved reservoir is simplified into two cases: (1) a single-cave and single-fracture series model composed of a single-cave and a single-fracture and (2) a composite model of dissolved caves and surrounding fracture networks. Note that the flow in a large cave is considered as free flow due to its large scale. The flow in a large fracture connected to the cave is considered as flow through porous media, and the flow in the reservoir surrounding the fracture network is considered as multiple-porosity model seepage flow. The corresponding seepage-free flow coupling mathematical model of different fractured-caved reservoirs has been established on this basis. We also obtained the rate transient analysis type curves of the oil well, conducted sensitivity analysis of each parameter, constructed the corresponding rate transient analysis curves, analyzed sensitivities of each parameter, and finally designed a dynamic evaluation method of well and reservoir parameters for different types of fractured-caved carbonate reservoirs. This study extensively applies this method in the Halahatang Oilfield of China and evaluates parameters such as reservoir reserves and physical properties to provide rational guidance for developing fractured-caved carbonate reservoirs.
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Dershowitz, Bill, Paul LaPointe, Thorsten Eiben e Lingli Wei. "Integration of Discrete Feature Network Methods With Conventional Simulator Approaches". SPE Reservoir Evaluation & Engineering 3, n. 02 (1 aprile 2000): 165–70. http://dx.doi.org/10.2118/62498-pa.
Testo completoAbstract (sommario):
Summary The discrete feature network (DFN) approach offers many key advantages over conventional dual porosity (DP) approaches, particularly when issues of connectivity dominate recovery and reservoir stimulation in fractured and heterogeneous reservoirs. DP models have been developed for complex multiphase and thermal effects, and have been implemented for basin scale modeling. However, DP models address only the dual porosity nature of fractured reservoirs, generally simplifying connectivity and scale-dependent heterogeneity issues which are modeled efficiently and more accurately by the DFN approach. This paper describes the development of techniques to integrate DFN and DP approaches. These techniques allow the analyst to maintain many of the advantages of the DP simulator approach without losing the realism of complex fracture system geometry and connectivity, as captured by DFN models. The techniques described are currently used within a DOE funded research project for linking a DFN and a DP thermal simulation model for the Yates field, Texas. The paper describes some of the geological and engineering aspects of the Yates field and gives two examples of how DP parameters for the thermal simulation can be derived using DFN modeling techniques. Introduction Reservoir simulation can be significantly more challenging for fractured reservoirs than it is for conventional clastic reservoirs. The dual porosity (DP) approach for the simulation of fractured reservoirs adds a second interacting continuum to reflect storage and permeability characteristics but does not adequately address connectivity issues. These effects, which play a key role in fractured reservoirs, are generally better addressed by discrete feature network (DFN) models.1 Another advantage of DFN models is that they are generally implemented as stochastic models, in which multiple realizations provide a quantitative measure for uncertainty and variability. Despite the significant simplifications made regarding the geometry of the fracture network in equivalent porous medium DP models (Fig. 1) and the recent progress made in developing powerful DFN modeling software, DP models still offer advantages regarding the level of sophistication of available multiphase flow solvers. In many cases, DP models also offer advantages regarding model size and speed. As a result, there is a need to link DP and DFN models to be able to take maximum advantage of each approach. This paper presents a series of techniques, which can be used to develop DP models that more accurately reflect the anisotropy, heterogeneity, and most important, the scale-dependent connectivity structure of fractured reservoirs. These techniques will allow the DP approach to take advantage of some of the features of the DFN approach. The approach adopted is to derive grid cell and well parameters through DFN models. The first section of this paper discusses which fracture porosity parameters can be derived for DP models from DFN models and how they are derived. The second section describes different techniques that can be used to link DP and DFN models. At the end of the paper two examples are given based on data from the Yates field, Texas. DP Input Parameter from DFN Modeling Fracture System Porosity. The fracture system porosity fF can be directly calculated as the product of the fracture intensity expressed as fracture area per unit volume (P32) and the storage aperture of the fractures (e):… Because the fracture system porosity depends on the number of fractures per unit volume, the fracture size distribution and the fracture aperture distribution, a different porosity needs to be calculated for every portion of the continuum model where these parameters vary. Using a full field DFN model, the fracture system porosity can be calculated separately for each grid cell. The primary issue in definition of fracture porosity from fracture intensity P32 is the selection of an appropriate measure for storage aperture e. Possible measures include:aperture derived from transient hydraulic response,mechanical aperture,aperture derived from fracture permeability or transmissivity ("cubic law"),aperture derived from geophysical measurements (gamma density, matrix porosity), andcorrelations to fracture size and orientation. Directional Fracture System Permeability. The permeability of the fracture system depends on the fracture intensity, the connectivity of the fracture network, and the distribution of fracture transmissivities. Approaches for calculation of approximate measures of grid cell effective directional permeability include the tensor approach of Oda,2 and the use of DFN simulations with a range of orientations for a unit gradient. Oda's2 method begins by considering the orientation of fractures in a grid cell, expressed as a unit normal vector n. Integrating the fractures over all of the unit normals N, Oda obtained the mass moment of inertia of fracture normals distributed over a unit sphere: ….For a specific grid cell with known fracture areas Ak and transmissivities Tk obtained from the DFN model, an empirical fracture tensor can be calculated by adding the individual fractures weighted by their area and transmissivity:…. Oda's permeability tensor is derived from Fij by assuming that Fij expresses fracture flow as a vector along the fracture's unit normal. Assuming that fractures are impermeable in a direction parallel to their unit normal, Fij must be rotated into the planes of permeability ….
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Grasmueck, Mark, Tijmen Jan Moser, Michael A. Pelissier, Jan Pajchel e Kenri Pomar. "Diffraction signatures of fracture intersections". Interpretation 3, n. 1 (1 febbraio 2015): SF55—SF68. http://dx.doi.org/10.1190/int-2014-0086.1.
Testo completoAbstract (sommario):
Fractured rock causes diffractions, which are often discarded as noise in ground-penetrating radar (GPR) and seismic data. Most fractures are too thin, too steep, and their displacement is too small to be imaged by reflections, and diffractions are the only detectable signal. To decipher the information about fracture geometry and distribution contained in diffractions, we compare 3D synthetic ray-Born modeling with high-density 3D GPR data and outcrop observations from the Cassis Quarry in Southern France. Our results reveal how the intersection between two fractures is the basic geologic element producing a recordable diffraction. In this new model, two intersecting fractures are represented by one finite-length line diffractor. The intersection of three fractures is a 3D cross composed of three line diffractors. Fractures extending over several meters in the outcrop display linear clusters of diffraction circles in unmigrated GPR time slices. Such large-scale fracture intersections are composed of many aligned short subwavelength line diffractors due to fracture roughness and variations of fracture opening. The shape irregularities and amplitude variations of composite diffraction signatures are a consequence of the geometry and spacing of the intersecting fractures generating them. With three simple base-type intersecting fracture models (horizontal dip, gentle dip, and steep dip), the fracture network geometry can be directly deciphered from the composite diffraction signatures visible on unmigrated time slices. The nonrandom distribution of diffractions is caused by fracture trends and patterns providing information about fracture dip, spacing, and continuity of fractured domains. With the similarity law, the diffraction phenomena observed in GPR data are very similar in character to those seen on the seismic scale with the wavelength as the scaling link. GPR data serve as a proxy to decipher seismic diffractions.
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Abdul-Razaq, Dr Sahar Abdul-Razaq. "A clinical Study of Complete and Partial Denture Fracture at Four Hospitals in Iraq". Mustansiria Dental Journal 9, n. 2 (4 marzo 2018): 201–7. http://dx.doi.org/10.32828/mdj.v9i2.265.
Testo completoAbstract (sommario):
Objective: To analyzes and determines the prevalence of type of denture fracture infour hospitals.Method: Data were collected from patients who attended prosthodontic clinics fordenture repairs at four hospitals. For each patient requiring of a fractured completeand partial denture, the variables were recorded: causes of denture fracture, thetype of fracture and the history of previous recurrent fractures.Results: Of 560 repaired denture 330 (59%) were complete dentures, 160 (30%) wereremovable partial denture, which were excluded from the study, and 70(10%) involved replacement of the teeth that had debonded from the denturebases. The ratio of upper to lower complete denture fractures was approximately2:1, most of the fractured dentures (65%) were those of males.Poor fit appeared to be the main cause of denture fracture 120 (20%), and poorocclusion was the second most common case recorded 50 (8%) .Midline fracturewas the most common type of fracture during the period of study 210(40%). Mostof fracture the fractured dentures 180 (32%) had previously been repaired once ormore.Conclusion: The total number of complete denture fractures was considerablyenhanced by repetitive fractures, which can be reduced by the application ofprosthetic principles in constructing and maintaining dentures particular during thelaboratory stages.Improvements in the processing techniques and the type of resin can reduce theincidence of denture fracture .Various polymers have been developed for use asdenture base resins to overcome some of the mechanical deficiencies ofpolymethylmethacrylate .
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Thakur, Vidhi, Shweta Mittal e Ritika Yadav. "Management of Complicated Crown Fracture with Biodentine Partial Pulpotomy and Fracture Segment Reattachment". International Journal of Health Sciences and Research 11, n. 6 (10 giugno 2021): 152–56. http://dx.doi.org/10.52403/ijhsr.20210623.
Testo completoAbstract (sommario):
Fracture of maxillary anterior teeth is common in young individuals. Conservative management of complicated crown fractures helps in preservation of tooth structure, vitality and esthetics. This case report describes a conservative technique of managing a case of complicated crown fracture by performing partial pulpotomy with biodentine followed by fracture segment reattachment. Key words: Complicated crown fracture, Partial pulpotomy, Fractured segment reattachment.
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Zheng, Yongxiang, Jianjun Liu e Yun Lei. "The Propagation Behavior of Hydraulic Fracture in Rock Mass with Cemented Joints". Geofluids 2019 (27 giugno 2019): 1–15. http://dx.doi.org/10.1155/2019/5406870.
Testo completoAbstract (sommario):
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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Gray, Sarah N., Mathieu Spriet, Tanya C. Garcia, Francisco A. Uzal e Susan M. Stover. "Preexisting lesions associated with complete diaphyseal fractures of the third metacarpal bone in 12 Thoroughbred racehorses". Journal of Veterinary Diagnostic Investigation 29, n. 4 (19 aprile 2017): 437–41. http://dx.doi.org/10.1177/1040638717704866.
Testo completoAbstract (sommario):
We characterized features of complete diaphyseal fractures of third metacarpal bones in Thoroughbred racehorses. Given that stress fractures are known to occur in the third metacarpal bone, an additional aim was to determine if complete fractures are associated with signs of a preexisting incomplete stress fracture. Bilateral metacarpi from 12 Thoroughbred racehorses euthanized because of complete unilateral metacarpal diaphyseal fracture were examined visually and radiographically. Open, comminuted, transverse or short oblique fractures occurred in the middle of the diaphysis or supracondylar region. Periosteal surface discoloration and bone callus formation contiguous with the fracture line were present in fractured bones. All contralateral intact metacarpi had gross anatomic lesions, and 10 had radiographic abnormalities similar to those observed on fractured metacarpi. Catastrophic metacarpal fractures occurred in racehorses with bilateral evidence of preexisting bone injury.
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Kelishadi, Shahrooz S., Matthew R. Zeiderman, Karan Chopra, Joseph A. Kelamis, Gerhard S. Mundinger e Eduardo D. Rodriguez. "Facial Fracture Patterns Associated with Traumatic Optic Neuropathy". Craniomaxillofacial Trauma & Reconstruction 12, n. 1 (marzo 2019): 39–44. http://dx.doi.org/10.1055/s-0038-1641172.
Testo completoAbstract (sommario):
Traumatic optic neuropathy (TON) is rare. The heterogeneity of injury patterns and patient condition on presentation makes diagnosis difficult. Fracture patterns associated with TON have never been evaluated. Retrospective review of 42 patients diagnosed with TON at the R. Adams Cowley Shock Trauma Center from May 1998 to August 2010 was performed. Thirty-three patients met criteria for study inclusion of fracture patterns. Additional variables measured included patient demographics and mechanism. Cluster analysis was used to form homogenous groups of patients based on different fracture patterns. Fracture frequency was analyzed by group and study population. Visual depiction of fracture patterns was created for each group. Cluster analysis of fracture patterns yielded five common “groups” or fracture patterns among the study population. Group 1 ( n = 3, 9%) revealed contralateral lateral orbital wall (100%), zygoma (67%), and nasal bone (67%) fractures. Group 2 ( n = 7, 21%) demonstrated fractures of the frontal bone (86%), nasal bones (71%), and ipsilateral orbital roof (57%). Group 3 ( n = 14, 43%) involved fractures of the ipsilateral zygoma (100%), lateral orbital wall (29%), as well as frontal and nasal bones (21% each). Group 4 ( n = 5, 15%) consisted of mid- and upper-face fractures; 100% fractured the ipsilateral orbital floor, medial and lateral walls, maxilla, and zygoma; 80% fractured the orbital roof and bilateral zygoma. Group 5 ( n = 4, 12%) was characterized by fractures of the ipsilateral orbital floor, medial and lateral orbital walls (75% each), and orbital roof (50%). A notably high 15 of 33 patients (45%) sustained penetrating trauma. Our study demonstrates five fracture pattern groups associated with TON. Zygomatic, frontal, nasal, and orbital fractures were the most common. Fractures with a combination of frontal, nasal, and orbital fractures are particularly concerning and warrant close attention to the eye.
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Wang, Shen, Huamin Li e Dongyin Li. "Numerical Simulation of Hydraulic Fracture Propagation in Coal Seams with Discontinuous Natural Fracture Networks". Processes 6, n. 8 (1 agosto 2018): 113. http://dx.doi.org/10.3390/pr6080113.
Testo completoAbstract (sommario):
To investigate the mechanism of hydraulic fracture propagation in coal seams with discontinuous natural fractures, an innovative finite element meshing scheme for modeling hydraulic fracturing was proposed. Hydraulic fracture propagation and interaction with discontinuous natural fracture networks in coal seams were modeled based on the cohesive element method. The hydraulic fracture network characteristics, the growth process of the secondary hydraulic fractures, the pore pressure distribution and the variation of bottomhole pressure were analyzed. The improved cohesive element method, which considers the leak-off and seepage behaviors of fracturing liquid, is capable of modeling hydraulic fracturing in naturally fractured formations. The results indicate that under high stress difference conditions, the hydraulic fracture network is spindle-shaped, and shows a multi-level branch structure. The ratio of secondary fracture total length to main fracture total length was 2.11~3.62, suggesting that the secondary fractures are an important part of the hydraulic fracture network in coal seams. In deep coal seams, the break pressure of discontinuous natural fractures mainly depends on the in-situ stress field and the direction of natural fractures. The mechanism of hydraulic fracture propagation in deep coal seams is significantly different from that in hard and tight rock layers.
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Zidane, Ali, e Abbas Firoozabadi. "Fracture-Cross-Flow Equilibrium in Compositional Two-Phase Reservoir Simulation". SPE Journal 22, n. 03 (3 gennaio 2017): 950–70. http://dx.doi.org/10.2118/184402-pa.
Testo completoAbstract (sommario):
Summary Compositional two-phase flow in fractured media has wide applications, including carbon dioxide (CO2) injection in the subsurface for improved oil recovery and for CO2 sequestration. In a recent work, we used the fracture-crossflow-equilibrium (FCFE) approach in single-phase compressible flow to simulate fractured reservoirs. In this work, we apply the same concept in compositional two-phase flow and show that we can compute all details of two-phase flow in fractured media with a central-processing-unit (CPU) time comparable with that of homogeneous media. Such a high computational efficiency is dependent on the concept of FCFE, and the implicit solution of the transport equations in the fractures to avoid the Courant-Freidricks-Levy (CFL) condition in the small fracture elements. The implicit solution of two-phase compositional flow in fractures has some challenges that do not appear in single-phase flow. The complexities arise from the upstreaming of the derivatives of the molar concentration of component i in phase α(cα,i) with respect to the total molar concentration (ci) when several fractures intersect at one interface. In addition, because of gravity, countercurrent flow may develop, which adds complexity when using the FCFE concept. We overcome these complexities by providing an upstreaming technique at the fracture/fracture interface and the matrix/fracture interface. We calculate various derivatives at constant volume V and temperature T by performing flash calculations in the fracture elements and the matrix domain to capture the discontinuity at the matrix/fracture interface. We demonstrate in various examples the efficiency and accuracy of the proposed algorithm in problems of various degrees of complexity in eight-component mixtures. In one example with 4,300 elements (1,100 fracture elements), the CPU time to 1 pore volume injection (PVI) is approximately 3 hours. Without the fractures, the CPU time is 2 hours and 28 minutes. In another example with 7,200 elements (1,200 fracture elements), the CPU time is 4 hours and 8 minutes; without fractures in homogeneous media, the CPU time is 2 hours and 53 minutes.
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Landine, Jim, Robert McGraw e William Pickett. "Clinical diagnosis of clavicle fractures: a pilot study". CJEM 3, n. 02 (aprile 2001): 95–98. http://dx.doi.org/10.1017/s1481803500005315.
Testo completoAbstract (sommario):
ABSTRACTObjective:Clavicle fractures are commonly encountered in the emergency department (ED). Our objective was to determine whether emergency physicians can clinically predict the presence and location of a clavicle fracture prior to obtaining x-rays.Methods:Over a 16-month period we prospectively studied ED patients who had injuries compatible with a clavicle fracture. Following clinical examination and prior to obtaining radiographs, ED physicians or senior emergency medicine (EM) residents were asked to predict whether the clavicle was fractured and, if fractured, the location of the fracture. Clinical predictions were later compared to the radiologist’s report.Results:Between April 1999 and August 2000, 184 patients with possible clavicle fracture were seen and 106 (58%) were enrolled. Of these, 94 had an acute fracture, and all 94 fractures were predicted on clinical grounds prior to x-ray. In 6 cases, physicians predicted a fracture but the radiograph was negative. In 6 additional cases, physicians were clinically unsure and the radiograph was negative. Physicians correctly predicted fracture location in 83 of 94 cases (88%; 95% confidence interval [CI], 82%–95%). In the 64 cases where physicians predicted a middle third fracture, they were 100% accurate (95% CI, 95%–100%). Errors made by physicians were conservative; that is, they occasionally predicted fractures in patients with only soft tissue injury, but they did not “miss” existing fractures.Conclusions:The results of this pilot study suggest that ED physicians can clinically predict the presence and location of clavicle fractures with a high degree of accuracy. It may be that x-rays are not always necessary in patients suspected of having a clavicle fracture. Future studies should define the indications for diagnostic radiography in patients with suspected clavicle fractures.
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Mizuhashi, Fumi, Yuko Watarai e Ichiro Ogura. "Diagnosis of Vertical Root Fractures in Endodontically Treated Teeth by Cone-Beam Computed Tomography". Journal of Imaging 8, n. 3 (23 febbraio 2022): 51. http://dx.doi.org/10.3390/jimaging8030051.
Testo completoAbstract (sommario):
The purpose of this study was to investigate the characteristics and the detection ability of vertical root fractures in endodontically treated teeth by intraoral radiography and cone-beam computed tomography (CBCT). CBCT images of 50 patients with root fractures in endodontically treated teeth were reviewed, and 36 vertical root fractures were taken in this study. The cause of fracture, core construction, kind of teeth, and fracture direction (bucco-lingual and mesio-distal fractures) were investigated. Detection ability of vertical root fractures by intraoral radiography and CBCT was also examined. Statistical analyses concerning the characteristics were performed by χ2 test, and the detection ability was analyzed by cross-tabulation. All of the fractured teeth were nontraumatized teeth. The vertical root fracture occurrence was not differed by core construction. The vertical root fracture number was largest at the premolar teeth (p = 0.005), and the number of the bucco-lingual fracture was larger than the mesio-distal fracture (p = 0.046). Vertical root fractures were detectable using CBCT, while undetectable by intraoral radiography (p < 0.001). Vertical root fractures occurred easily in premolar teeth with bucco-lingual direction, and CBCT is an adequate radiographic method to diagnose vertical root fracture.
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Chang, Xu, Junjie Liu, Chun An Tang, Yong Bin Zhang e Juan Xia Zhang. "Numerical Approach to Fracture Spacing in Two Layered Material". Key Engineering Materials 297-300 (novembre 2005): 750–55. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.750.
Testo completoAbstract (sommario):
Equally spaced opening-mode fractures always evolve in top layer attached to underlying layer. With a newly developed Material Failure Process Analysis code (MFPA2D), we have firstly investigated the stress distribution between two adjacent fractures as a function of the fracture-spacing-to-layer-thickness ratio using a two-layer model with a fractured top layer. The numerical results indicate the horizontal stress perpendicular to the fractures near the top surface changes from tensile to compressive when the fracture-spacing-to-layer-thickness ratio changes from greater than to less than a critical value. Then, the process from fracture initiation to fracture saturation is numerically modeled. The modeling of fracture process shows that the fractures initiate at the top surface and propagate to the interface between the two layers in the first stage. In the following stage, new fractures can infill between the earlier formed fractures and they always initiate at the interface and propagate to the top surface. Numerical simulation clearly demonstrates that the stress state transition precludes further infilling of fractures and the fracture spacing reaches a constant state, i.e. the so-called fracture saturation.
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Kharrat, Riyaz, Nouri Alalim e Holger Ott. "Assessing the Influence of Fracture Networks on Gas-Based Enhanced Oil Recovery Methods". Energies 16, n. 17 (2 settembre 2023): 6364. http://dx.doi.org/10.3390/en16176364.
Testo completoAbstract (sommario):
Numerous reservoirs that play a significant role in worldwide petroleum production and reserves contain fractures. Typically, the fractures must form a connected network for a reservoir to be classified as naturally fractured. Characterizing the reservoir with a focus on its fracture network is crucial for modeling and predicting production performance. To simplify the solution, dual-continuum modeling techniques are commonly employed. However, to use continuum-scale approaches, properties such as the average aperture, permeability, and matrix fracture interaction parameters must be assigned, making it necessary to improve the fracture depiction and modeling methods. This study investigated a fractured reservoir with a low matrix permeability and a well-connected fracture network. The focus was on the impact of the hierarchical fracture network on the production performance of gas-based enhanced oil recovery methods. The discrete fracture network (DFN) model was utilized to create comprehensive two-dimensional models for three processes: gas injection (GI), water alternating gas (WAG), and foam-assisted water alternating gas (FAWAG). Moreover, dimensionless numbers were employed to establish connections between properties across the entire fracture hierarchy, spanning from minor to major fractures and encompassing the fracture intensity. The results indicate that the FAWAG process was more sensitive to fracture types and networks than the WAG and GI processes. Hence, the sensitivity of the individual EOR method to the fracture network requires a respective depth of description of the fracture network. However, other factors, such as reservoir fluid properties and fracture properties, might influence the recovery when the minor fracture networks are excluded. This study determined that among the enhanced oil recovery (EOR) techniques examined, the significance of the hierarchical depth of fracture networks diminished as the ratio of major (primary fracture) aperture to the aperture of medium and minor fractures increased. Additionally, the impact of the assisted-gravity drainage method was greater with increased reservoir height; however, as the intensity ratio increased, the relative importance of the medium and minor fracture networks decreased.
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Jia, Pin, Defeng Wu, Hengfei Yin, Zhuang Li, Linsong Cheng e Xianzhe Ke. "A Practical Solution Model for Transient Pressure Behavior of Multistage Fractured Horizontal Wells with Finite Conductivity in Tight Oil Reservoirs". Geofluids 2021 (19 giugno 2021): 1–10. http://dx.doi.org/10.1155/2021/9948505.
Testo completoAbstract (sommario):
Fractured horizontal wells have been widely used to develop unconventional oil and gas reservoirs. In previous studies, most studies on the transient pressure behavior of multistage horizontal wells were based on the assumption of single porosity medium, in which the coupling relationship of natural fractures and artificial fractures was not taken into account or artificial fractures were assumed to be infinitely conductive. In this paper, the fracture is finite conductive, which means that there is flow resistance in the fracture. Based on point-source method and superposition principle, a transient model for multistage fractured horizontal wells, which considers the couple of fracture flow and reservoir seepage, is built and solved with the Laplace transformation. The transient pressure behavior in multistage fractured horizontal wells is discussed, and effects of influence factors are analyzed. The result of this article can be used to identify the response characteristic of fracture conductivity to pressure and pressure differential and provide theoretical basis for effective development of tight oil reservoirs. The findings of this study can help for better understanding of transient pressure behavior of multistage fractured horizontal wells with finite conductivity in tight oil reservoirs.
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Larcombe, T., R. A. Lisk e K. F. Yeong. "72 Surviving the Epidemic That Confronts Us—Fracture Liaison Service Evaluation Data". Age and Ageing 50, Supplement_1 (marzo 2021): i12—i42. http://dx.doi.org/10.1093/ageing/afab030.33.
Testo completoAbstract (sommario):
Abstract Introduction 1 in 2 women and 1 in 5 men over the age of 50 will break a bone and a significant proportion will suffer from osteoporosis.A fragility fracture will double the risk of future fractures. Between 1990 and 2000, there was nearly a 25% increase in hip fractures worldwide. A hip fracture is one of the most devastating, and often terminal, injury for an older person. Intervention The Fracture Liaison Service (FLS) captures patients aged 50 and above that present to fracture clinic with possible fragility fractures with the aim to reduce further fracture incidence. Patients are assessed for osteoporosis and recommendations made for treatment. Results Here we present the results of our FLS service evaluation after 6 years in operation, using the rate of hip fractures (number of hip fractures/Emergency Department [ED] attendances over 75’s) as a surrogate marker for effectiveness. Evaluation Summary Trend analysis of our data indicates a reduction in the number of patients attending the Trust with fractured neck of femur (NOF) despite the increase in ED attendances. This is against the trend nationally where fractured NOF numbers are rising (National Hip Fracture Database, accessed online August 2019). Next steps The FLS to attempt to comprehensively capture muscular-skeletal patients and to consider opportunities present to target case finding to high risk cohorts.
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Liu, Mengxuan. "Research on fracture trend of repeated fracturing". Journal of Physics: Conference Series 2247, n. 1 (1 aprile 2022): 012016. http://dx.doi.org/10.1088/1742-6596/2247/1/012016.
Testo completoAbstract (sommario):
Abstract The fracture trend of repeated fracturing is directly related to the effect of repeated fracturing and whether it can effectively expand the swept volume. In this paper, a large-scale hydraulic fracturing process simulation device is used to conduct laboratory experiments on fractured reservoirs to study the initiation and extension of repeated fracturing fractures under different stress states. The experimental results show that new fractures are easy to extend from the natural fractures near the wellbore, and the initiation pressure of the secondary fracturing is reduced due to the inducing effect of the initial fractures. The conclusion has a certain guiding function for the prediction of repeated fracturing fracture propagation in field fractured reservoirs, and it is of great significance for fracturing construction.
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Noor, Marjan, Raheel Hassan, Abid Hussain Bukhari e Rashida Hilal. "Frequency of Parasymphysis Fracture in Mandibular Fractures Due to Road Traffic Accidents". Pakistan Journal of Medical and Health Sciences 16, n. 9 (30 settembre 2022): 333–34. http://dx.doi.org/10.53350/pjmhs22169333.
Testo completoAbstract (sommario):
Objective: To determine the frequency of parasymphysis fracture in mandibular fractures due to road traffic accidents. Study Type: Cross-sectional study Duration and Place of Study: Department of OMF Surgery Ayub Teaching Hospital, Abbottabad from 1st December 2019 to 30thMay 2020 Methodology: One hundred and forty eight patients were shifted to the Radiology Department for X-rays of mandible . Fractures of mandible especially fracture of parasymphysis were seen. Results: The mean age was 47.46±21.25 years. Fractured parasymphysis was found in 75 (82%) male patients and female patients were 14% (8/57). Conclusions: The gender was found to be significantly associated with the outcome i.e. parasymphysis fracture in mandibular fractures due to road traffic accidents. The age, number of fractures and type of fractures were not found to be significantly associated with the outcome i.e. parasymphysis fracture in mandibular fractures due to road traffic accidents. Keywords: Parasymphysis fracture, Mandibular fractures, Facial injury
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Jian, Shikai, Liyun Fu e Yifan Cheng. "Anisotropic Effective Elastic Properties for Multi-Dimensional Fractured Models". Applied Sciences 12, n. 4 (11 febbraio 2022): 1873. http://dx.doi.org/10.3390/app12041873.
Testo completoAbstract (sommario):
The size, distribution, and orientation of fractures are generally multiscale and multi-dimensional in nature, leading to complex anisotropic characteristics. Theoretical or semi-analytical methods to determine the effective elastic properties depend on several assumptions, including the absence of the stress interaction and idealized fractures. On the basis of finite-element models, we conduct numerical oscillatory relaxation tests for determining the effective elastic properties of fractured rocks. The numerical approach for calculating equivalent stiffness tensors in two-dimensions is compared to the theoretical models for different fracture densities. Due to fracture interactions at high fracture densities, the suggested model makes a physical prediction. The effective elastic properties obtained from the application to a real fractured model, established from an outcrop, obviously disperse at different frequencies, which can be used to investigate fracture interactions and dynamic stress disturbances. The algorithm is extended to three-dimensional cases and also validated by using conventional effective medium theories. It is found that the fracture density obviously impacts the effective anisotropy properties, and the proposed method gives a reasonable prediction for high-fracture density. This work is significant because it enables the calculation of effective elastic properties of multi-dimensional fractured models and the fracture interaction mechanism.