共查询到20条相似文献，搜索用时 31 毫秒
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We introduce a discrete fracture network model of stationary Darcy flow in fractured rocks. We approximate the fractures by a network of planar circle disks, which is generated on the basis of statistical data obtained from field measurements. We then discretize this network into a mesh consisting of triangular elements placed in three-dimensional space. We use geometrical approximations in fracture planes, which allow for a significant simplification of the final triangular meshes. We consider two-dimensional Darcy flow in each fracture. In order to accurately simulate the channeling effect, we assign to each triangle an aperture defining its hydraulic permeability. For the discretization we use the lowest order Raviart-Thomas mixed finite element method. This method gives quite an accurate velocity field, which is computed directly and which satisfies the mass balance on each triangular element. We demonstrate the use of this method on a model problem with a known analytical solution and describe the generation and triangulation of the fracture network and the computation of fracture flow for a particular real situation. 相似文献
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The objective of this investigation is to characterize the influence of the loading rate, scratch speed, mineralogy, morphology, anisotropy, and total organic content on the scratch toughness of organic-rich shale. We focus our study on a gray shale, Toarcian shale (Paris basin, France) and a black shale, Niobrara shale (northeastern Colorado, USA). Microscopic scratch tests are performed for varying scratch speeds and loading rates. We consider several orientations for scratch testing. For all gas shale specimens, the scratch toughness is found to increase with increasing scratch speed. In the asymptotic regime of high speeds, there is a convergence toward a single constant value irrespective of the loading rate. To understand this evolution of the scratch toughness, a nonlinear fracture mechanics model is built that integrates fracture dissipation with the various forms of viscous processes. In particular, a coupling is shown between the fracture energy and the viscoelastic characteristics. An inverse approach which combines scratch and indentation testing makes it possible to represent all tests in a single curve and retrieve the rate-independent fracture toughness of kerogen-rich shale materials. The presence of organic matter drastically alters the creep and fracture properties at the microscopic length-scale. The fracture behavior is anisotropic with the divider orientation yielding the highest fracture toughness value and the short transverse orientation yielding the lowest fracture toughness. Elucidating the fracture-composition-morphology relationships in organic-rich shale will promote advances in science and engineering for energy-related applications such as hydraulic fracturing in unconventional reservoirs or \(\hbox {CO}_2\) sequestration in depleted reservoirs. 相似文献
4.
We develop a new analytical model, called OpenT, that solves the elasticity problem of a hydraulic fracture (HF) contact with a pre-existing discontinuity natural fracture (NF) and the condition for HF re-initiation at the NF. The model also accounts for fluid penetration into the permeable NFs. For any angle of fracture intersection, the elastic problem of a blunted dislocation discontinuity is solved for the opening and sliding generated at the discontinuity. The sites and orientations of a new tensile crack nucleation are determined based on a mixed stress- and energy-criterion. In the case of tilted fracture intersection, the finite offset of the new crack initiation point along the discontinuity is computed. We show that aside from known controlling parameters such stress contrast, cohesional and frictional properties of the NFs and angle of intersection, the fluid injection parameters such as the injection rate and the fluid viscosity are of first-order in the crossing behavior. The model is compared to three independent laboratory experiments, analytical criteria of Blanton, extended Renshaw?Pollard, as well as fully coupled numerical simulations. The relative computational efficiency of OpenT model (compared to the numerical models) makes the model attractive for implementation in modern engineering tools simulating hydraulic fracture propagation in naturally fractured environments. 相似文献
5.
Geologic Stochastic Modeling and Connectivity Assessment of Fracture Systems in the Boston Area 总被引：8，自引：4，他引：8
Summary
The MIT stochastic model for representing fracture patterns has been applied to the Boston area. The model is a geometric-mechanical
model, which means that underlying mechanisms are geometrically represented. In this paper the model is calibrated by comparing
the fracture spacing and trace length simulated by the model with data collected by Billings (1976) in a number of tunnels
in the Boston area. Following this, geometric fracture connectivity is investigated. This is done by recording in the model
simulations, the number of interconnected fractures in so called sub-networks and by recording the geometric extents of these
sub-networks. The results indicate limited horizontal but large vertical connectivity. 相似文献
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The representation of the surface of a rock fracture and a numerical method to simulate fluid flow in single fractures are the keys to understanding the hydraulic behaviour of rock fractures. In this paper, a cellular automaton (CA) approach is used to generate the single fracture structure, which is assumed to be composed of contacts and voids. We develop a CA evolution rule to produce a contact area, and randomly model a single rock fracture with different contact ratios to reflect natural fracture properties such as dead voids, islands and tortuous flow path. Then, based on the localisation theory of a CA, a numerical method to simulate fluid flow in single fractures with contacts is developed. In this method, the fracture is discretised into a system composed of cell elements. Different apertures, i.e., zero for contacts and non-zero for voids, are assigned to each cell element. Therefore, the contribution of the cell elements in a contact on a cell’s transmissivity can be ignored completely. The local transmissivity is assumed to conform to the cubic law. The fluid flow in a fracture with different contact situations is then modelled using the method established in this paper. The fluid flow path, flow velocity and fluid head distributions as well as the channel flow in the fracture are well-modelled. The flow behaviour of the fracture strongly depends on the effective fluid flow path. 相似文献
8.
页岩作为典型的非常规储层,基质孔隙小,渗透率极低,水平井多级水力压裂为其商业开发的主要手段。准确模拟页岩气产能,应同时考虑水力裂隙和天然裂隙的渗流。基于离散裂隙模型和等效连续模型建立页岩气渗流数学模型,利用有限元分析方法进行数值求解,研究不同走向裂隙组对页岩气井产能的影响。研究认为,页岩基质为气体的生产提供了主要气源,天然裂隙作为渗流的主要通道,将气体输送到水力裂缝,进而到达井筒。模拟结果表征,离散裂隙的渗流特征对于页岩气井的产能有重要影响。根据页岩储层的天然裂隙走向,可以优化相应的水平井方位。对于二维离散裂隙网络模型,水平井沿着2个裂隙组夹角的平分线更有利于生产。 相似文献
9.
Ma Lei Han Di Qian Jiazhong Gao Di Ma Haichun Deng Yaping Hou Xiaoliang 《Hydrogeology Journal》2023,31(4):913-930
The equivalent porous medium (EPM) method is an efficient approximation method for groundwater yield analysis considering the equivalent permeability in a fractured geologic medium (FGM). The EPM method is widely used in many practical hydrogeological problems from local to regional scales. However, when calculating water head and velocity distributions, the suitability of the EPM model remains insufficiently evaluated. The suitability refers to the head error caused by the application of the EPM model. The smaller the error, the better the suitability. In this study, the influence of fracture geometric attributes on the suitability was quantitatively studied in numerical simulation experiments, and the EPM model simulation results were compared to those obtained with the discrete fracture network (DFN) model. The results indicated that the suitability decreased with increasing fracture spacing. When the fracture spacing was smaller than 0.6 m, the influence of an increase in the fracture spacing on the suitability was obvious. For the same fracture spacing, the suitability generally increased with increasing trace length. When the spatial variability of fracture aperture is not considered, the change of the fracture aperture did not impact the suitability. The fracture orientation slightly impacted the suitability, which can be ignored. An evaluation standard based on fracture parameters is proposed to estimate the suitability of the EPM model, which provides a scientific basis to ascertain whether this model can be applied to a given site to solve the head-related hydrogeological issues with FGMs.
相似文献10.
在Hudson理论的基础上推导出基于弹性—声学近似的裂缝模型反射系数计算公式,然后用变参考慢度Rytov近似波场延拓算子,对给定裂缝模型进行正演和偏移,并分析其波场特征,得到以下三点结论:1在当前地震分辨率下,不能识别单个裂缝,但可以探测裂缝发育带;2裂缝带达到一定的宽度和密度,可以用地震方法检测裂缝的分布,潜山内幕反射波的范围与强弱,有利于研究裂缝发育带的宽度和密度;3裂缝带的低频复波反射,表明在裂缝发育带,地震波频率减低,意味着用地震波的频率特征是可以检测裂缝。 相似文献
11.
Upscaling methods such as the dual porosity/dual permeability (DPDP) model provide a robust means for numerical simulation of fractured reservoirs. In order to close the DPDP model, one needs to provide the upscaled fracture permeabilities and the parameters of the matrix-fracture mass transfer for every fractured coarse block in the domain. Obtaining these model closures from fine-scale discrete fracture-matrix (DFM) simulations is a lengthy and computationally expensive process. We alleviate these difficulties by pixelating the fracture geometries and predicting the upscaled parameters using a convolutional neural network (CNN), trained on precomputed fine-scale results. We demonstrate that once a trained CNN is available, it can provide the DPDP model closures for a wide range of modeling parameters, not only those for which the training dataset has been obtained. The performance of the DPDP model with both reference and predicted closures is compared to the reference DFM simulations of two-phase flows using a synthetic and a realistic fracture geometries. While the both DPDP solutions underestimate the matrix-fracture transfer rate, they agree well with each other and demonstrate a significant speedup as compared to the reference fine-scale solution.
相似文献12.
煤层气开采过程中储层渗透率的变化对产气量影响较大,通过引入S＆D渗透率变化模型,建立了考虑渗透率变化的煤储层三维气水两相渗流数学模型,完成模型检验后应用所编制软件研究了煤储层参数、吸附参数及渗透率模型特征参数对开发效果的影响。结果表明,煤层气产量随着初始含气量、煤层有效厚度、裂缝渗透率和Langmuir压力的增大而增大,随储层原始压力、裂缝孔隙度和Langmuir体积的增大而减小,而解吸时间对产气量影响不大;裂缝渗透率随着杨氏模量和基质收缩/膨胀系数的增大而增大,随泊松比和裂缝压缩系数的增大而减小。引入S＆D模型后计算的累积产气量要比常规模型低1.3%,因此不可忽视煤层气产出过程中渗透率的变化。 相似文献
13.
Coupled hydro-mechanical (HM) processes are significant in geological engineering such as oil and gas extraction, geothermal energy, nuclear waste disposal and for the safety assessment of dam foundations and rock slopes, where the geological media usually consist of fractured rock masses. In this study, we developed a model for the analysis of coupled hydro-mechanical processes in porous rock containing dominant fractures, by using the numerical manifold method (NMM). In the current model, the fractures are regarded as different material domains from surrounding rock, i.e., finite-thickness fracture zones as porous media. Compared with the rock matrix, these fractured porous media are characterized with nonlinear behavior of hydraulic and mechanical properties, involving not only direct (poroelastic) coupling but also indirect (property change) coupling. By combining the potential energy associated with mechanical responses, fluid flow and solid–fluid interactions, a new formulation for direct HM coupling in porous media is established. For indirect coupling associated with fracture opening/closure, we developed a new approach implicitly considering the nonlinear properties by directly assembling the corresponding strain energy. Compared with traditional methods with approximation of the nonlinear constitutive equations, this new formulation achieves a more accurate representation of the nonlinear behavior. We implemented the new model for coupled HM analysis in NMM, which has fixed mathematical grid and accurate integration, and developed a new computer code. We tested the code for direct coupling on two classical poroelastic problems with coarse mesh and compared the results with the analytical solutions, achieving excellent agreement, respectively. Finally, we tested for indirect coupling on models with a single dominant fracture and obtained reasonable results. The current poroelastic NNM model with a continuous finite-thickness fracture zone will be further developed considering thin fractures in a discontinuous approach for a comprehensive model for HM analysis in fractured porous rock masses. 相似文献
14.
地震导致山体变形破裂是一个复杂的演化过程,文中通过一些典型实例的地质分析,总结归纳了高地震烈度区山体变形破裂失稳有一定代表性的倾外层状体斜坡滑坡型、高陡块(层)状体斜坡崩塌型、软弱基座体斜坡滑坡型等3种典型性地质力学模式。自主创新研制、设计、探索了一套振动条件下地质力学模拟试验的设备模型和方法,并对3种典型性地质力学模型进行机制模拟试验。通过变形破裂演化过程模拟再现试验,从中揭示出一些振动条件下变形破裂的典型迹象和重要证据,充分再现了典型地震失稳机制的形成条件、相关性因素以及演化规律,为进一步研究分析提供科学可靠的试验数据和证据。 相似文献
15.
裂缝等效介质模型对裂缝结构和充填介质参数的适应性 总被引：1，自引：0，他引：1
基于裂缝各向异性等效介质模型：定量分析了纵横波速度、弹性刚度张量随裂缝密度、裂缝孔隙纵横比及孔隙充填流体性质的变化规律;考察了Hudson模型、Pade近似和Liu含裂缝介质模型的适用条件和精度;重点分析了裂缝孔隙的结构参数、孔隙度大小及充填流体性质对弹性模量和纵横波速度的影响。基于Hudson模型的Pade近似,明确了它对高裂缝密度和大纵横比的适应性。Hudson模型、Pade近似和Liu含裂缝介质模型的响应模拟表明：在裂缝密度小于0.1时,Liu模型和Hudson二阶近似的响应基本一致,Liu模型和Pade近似均适用于裂缝密度小于等于0.2的裂缝介质;裂缝密度大于0.2时,前者适应性更好些。另外,纵横比对饱水裂缝介质标准化刚度模量的影响较干裂缝介质的影响大。 相似文献
16.
Yan Jin Jianbo Yuan Mian Chen K. P. Chen Yunhu Lu Huaiying Wang 《Rock Mechanics and Rock Engineering》2011,44(5):621-627
Hydraulic fracture propagation is greatly influenced by mode-II fracture toughness since this is one of the factors which
determine whether a fracture diverts. Direct measurement of rock fracture toughness is constrained by high cost, limited number
of available cores and long turn around time. Therefore, to overcome these constrains, it is necessary to develop an effective
mode-II fracture toughness test which can be used in a prediction analysis for deep rock formations. Consequently, a mode-II
fracture toughness test system was designed for rocks using the straight-notched Brazilian disc (SNBD) test methodology. In
the experiment, this system was used to test 20 rock samples from the WG oilfield. This enabled a fracture toughness prediction
model to be established, based on an analysis of the test data. H341 acoustic, density and gamma-ray logging data were used
to predict horizontal stresses and rock tensile strength. When combined with the mode-II fracture toughness prediction model,
continuous values were predicted, which were successfully confirmed by field fracturing practices. It was confirmed, therefore,
that this successful method met the need of providing continuous fracture toughness data during field fracturing operations. 相似文献
17.
高放废物地质处置过程中涉及的核素在围岩裂隙地下水中的迁移问题已引起广泛关注,数值模拟是研究核素粒子运移的重要方法。目前裂隙介质中渗流模型主要是等效连续介质模型、双重介质模型和离散裂隙网络模型。对于岩体尺度裂隙地下水的流动,离散裂隙网络模型能充分表现裂隙介质的各向异性、不连续性等特征。因此,针对裂隙介质准确概化及核素迁移模拟等难点,文章结合Monte Carlo随机生成裂隙方法、裂隙渗流有限元算法和高放射性核素衰变方程等方法,依据花岗岩深钻孔裂隙统计数据,采用离散裂隙网络模型对内蒙古阿拉善高放废物地质处置预选区展开了核素粒子迁移数值模拟研究,并讨论了实例预测分析结果。结果显示:针对设定的地质模型,核素粒子从中心运移到边界的迁移路径长度平均为1293.35 m,粒子运移到边界耗费的时间平均为1.70E+11 d。 相似文献
18.
S. Seifollahi P. A. Dowd C. Xu A. Y. Fadakar 《Rock Mechanics and Rock Engineering》2014,47(4):1225-1235
Fracture network modelling plays an important role in many application areas in which the behaviour of a rock mass is of interest. These areas include mining, civil, petroleum, water and environmental engineering and geothermal systems modelling. The aim is to model the fractured rock to assess fluid flow or the stability of rock blocks. One important step in fracture network modelling is to estimate the number of fractures and the properties of individual fractures such as their size and orientation. Due to the lack of data and the complexity of the problem, there are significant uncertainties associated with fracture network modelling in practice. Our primary interest is the modelling of fracture networks in geothermal systems and, in this paper, we propose a general stochastic approach to fracture network modelling for this application. We focus on using the seismic point cloud detected during the fracture stimulation of a hot dry rock reservoir to create an enhanced geothermal system; these seismic points are the conditioning data in the modelling process. The seismic points can be used to estimate the geographical extent of the reservoir, the amount of fracturing and the detailed geometries of fractures within the reservoir. The objective is to determine a fracture model from the conditioning data by minimizing the sum of the distances of the points from the fitted fracture model. Fractures are represented as line segments connecting two points in two-dimensional applications or as ellipses in three-dimensional (3D) cases. The novelty of our model is twofold: (1) it comprises a comprehensive fracture modification scheme based on simulated annealing and (2) it introduces new spatial approaches, a goodness-of-fit measure for the fitted fracture model, a measure for fracture similarity and a clustering technique for proposing a locally optimal solution for fracture parameters. We use a simulated dataset to demonstrate the application of the proposed approach followed by a real 3D case study of the Habanero reservoir in the Cooper Basin, Australia. 相似文献
19.
The term boudinage is used to describe a wide variety of extensional structures in deformed rocks. This paper is mainly concerned with boudinage resulting from through-layer extension fractures followed by separation of the layer segments, thus forming boudins with more or less rectangular cross-sections. In principle, this process is similar to the break up of fibres in fibre-reinforced composite materials extended parallel to the fibre direction. Both processes are controlled by the transfer of stress from the matrix to the fibre (or layer) and a mathematical model for fibre-matrix stress transfer (the ‘fibre-loading’ model) is well established. We have used this as a basis for developing a stress transfer model for boudinage. The only difference in the basic mathematical formulation results from geometric differences between the two systems; the geometric expressions in the fibre-loading model have, therefore, been rederived for the layer-matrix case.Stress-transfer theory predicts that the tensile stress in a layer segment rises from a minimum at the end of a segment to a maximum at the centre. This behaviour, which is clearly shown by finite-element models of boudinage structure, suggests that extension fracture boudinage develops by successive ‘mid-point’ fracturing. According to stress-transfer theory, the process will continue until a layer is reduced to segments (boudins) all of which are shorter than some critical length (for which the tensile fracture strength of the layer is equal to the tensile stress at the mid-point). In practice, successive fracturing will be influenced by two other factors: (1) in nature the controlling material properties (tensile fracture strength, elastic moduli) will not be single-valued but will have a distribution reflecting local variations in lithology and microstructure and (2) major pre-deformation flaws may be present in a layer which will control the ‘starting length’ of layer segments. These factors are incorporated with the stress-transfer theory into a statistical (Monte Carlo) model for extension fracture boudinage which results in a prediction of boudin aspect ratios. The predicted distribution compares very closely with the observed distribution of 91 quartzite boudins within Lower Carboniferous slates at Tintagel, Cornwall.The stress-transfer model implies that boudin-defining fractures occur sequentially so that inter-boudin gap lengths will be unequal. Strain estimates based on boudinage structure will vary according to which part and how much of a layer is sampled. A much improved strain estimate is possible based on sequentially closing the inter-boudin gaps. The stress-transfer theory also leads to the possibility of estimating palaeostress from boudinage structure and is the only model available which predicts an aspect ratio distribution of boudins formed by extension fracture. Other than our own, we know of no published data on boudin aspect ratio distributions. Hence, further elaboration of the model is not possible until more field data is available. We hope that our work will encourage the systematic measurement of boudinage as well as the development of alternative models. 相似文献
20.
岩体内裂隙等非连续结构面对岩体的强度及变形等力学特性有着显著的影响,研究岩体裂隙起裂、扩展、相互作用和贯通机制,对工程岩体力学行为的表征和工程性能的评价十分重要。本文基于连续介质力学模型的离散元方法,通过考虑裂隙分布、模型加载条件及其与裂隙产状的关系,建立了一系列裂隙力学计算模型,研究了不同模型裂隙扩展演化特征和岩体破裂机制,分析了岩体裂隙扩展规律及其对岩体破坏路径和强度的影响,研究结果表明:（1）裂隙岩体模型加载条件下的破坏起裂点、最终贯通破坏特征及损伤分布受控于裂隙的产状及其与最大主压应力取向角度大小及围压大小。（2）裂隙弱面走向与最大主压应力取向斜交时,裂隙弱面在加载条件下其端部裂隙扩展、贯通破坏表现比较明显,反之,当裂隙弱面走向与最大主压应力取向一致时,裂隙弱面被动影响裂隙模型内新生裂隙的萌生、扩展和贯通模式,自身未出现新的扩展破坏。（3）裂隙数目的增多和围压的增大会显著增加模型内部剪切裂缝的数量和模型破坏后的破碎程度,模型内部的损伤区域主要围绕破裂面呈滑移线型交叉分布,非破裂面区域损伤呈条带状X型分布。（4）裂隙弱面走向与最大主压应力取向斜交时,裂隙对岩体模型强度的弱化程度高于裂隙弱面走向与最大主压应力取向一致的情况,而裂隙模型破坏后的残余强度则正好相反。 相似文献