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水平井分段体积压裂是页岩气商业规模开发的重要工艺措施,如何评价页岩储层可压性是该工艺成功的关键。页岩断裂韧性是可压性评价的重要支撑参数,从I型断裂裂纹（裂缝）微观形态入手,结合断裂力学理论和分形理论,建立了页岩I型断裂韧性分形计算方法;借助晶体劈裂功法计算页岩表面能,采用密度、声波时差2种参数获取计算结果,对比分析新的分形方法计算数据、传统方法预测数据与试验测试数据,新的分形方法计算平均误差为3.63%,传统预测方法平均误差为 %,验证了方法的准确性;参考实例水平井测井解释数据,计算了水平段I型断裂韧性指数的全井筒连续性剖面,结合可压性级别与较大储层改造体积概率关系,优选可压性级别为III级及II级改造。建立的页岩I型断裂韧性分形计算方法对定量评价页岩储层可压性具有重要意义。 相似文献
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We have developed a new approach for the numerical modeling of deformation processes combining brittle fracture and viscous flow. The new approach is based on the combination of two meshless particle-based methods: the discrete element method (DEM) for the brittle part of the model and smooth particle hydrodynamics (SPH) for the viscous part. Both methods are well established in their respective application domains. The two methods are coupled at the particle scale, with two different coupling mechanisms explored: one is where DEM particles act as virtual SPH particles and one where SPH particles are treated like DEM particles when interacting with other DEM particles. The suitability of the combined approach is demonstrated by applying it to two geological processes, boudinage, and hydrofracturing, which involve the coupled deformation of a brittle solid and a viscous fluid. Initial results for those applications show that the new approach has strong potential for the numerical modeling of coupled brittle–viscous deformation processes. 相似文献
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In the absence of initial cracks, the material behavior is limited by its strength, usually defined in homogeneous conditions (of stress and strain). Beyond this limit, in quasi‐brittle case, cracks may propagate and the material behavior tends to be well described by fracture mechanics. Discrete element approaches show consistent results dealing with this transition during rupture. However, the calibration of the parameters of the numerical models (i.e., stiffness, strength, and toughness) may be quite complex and sometimes only approximative. Based on a brittle rupture criterion, we analyze the biaxial response of uncracked samples. Thus, tensile and compressive strengths are analytically identified and become direct parameters of our discrete model. Furthermore, a physically reliable crack initiation (and subsequent propagation) is shown to be induced during rupture and verified by the simulation of three‐point bending and diametral compression tests. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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逆断层控制构造裂缝发育的力学机制模拟 总被引：1，自引：1，他引：0
在探讨逆断层对构造裂缝控制作用的基础上, 应用Comsol有限元软件, 模拟不同水平作用力、不同岩性、不同断层倾角和距断层面远近等因素影响下断层及其周边区域的应力、应变情况, 并分析了不同控制因素下构造裂缝发育的规律。模拟结果表明, 构造裂缝的发育程度随施加的水平应力作用增大而线性增大; 岩石破裂前产生的应变量可用来描述岩石的脆性, 抗压强度对岩石破裂起主导作用, 而岩石的抗剪强度与岩石破裂发育有一定的相关性; 逆断层倾角存在一个临界角度, 使构造裂缝发育最为强烈; 逆断层控制裂缝发育, 距离断裂面越远裂缝发育程度越低, 并存在一个发育程度骤减的范围, 称为"断裂控制带", 该断裂控制带的形成和分布应该与断裂的性质、规模、断距及岩石力学参数等有关。 相似文献
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An understanding of the fracture mechanics of geomaterials is important for the solution of many problems in geomechanics. One of the most important material properties involved in fracture mechanics is the fracture toughness, KIc. The short-rod test configuration proposed by Barker1 has significant potential for becoming a standard test for fracture toughness determination in geomechanics. The purpose of this brief is to examine the application potential of the short-rod test for geomechanics problems. 相似文献
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应用激光实时全息干涉法实现了钢纤维混凝土三点弯曲切口梁断裂全过程的实时动态观测研究,连续动态捕获了钢纤维混凝土试件的干涉条纹图。实时全息干涉条纹的动态特征和分布规律直观准确地演示了钢纤维混凝土的初裂点和各阶段的变形特征以及裂缝扩展全过程。试验研究表明,当混凝土试件的钢纤维掺量大于1.0 %时,钢纤维的阻裂增韧效应是明显的。钢纤维混凝土断裂力学参量的计算与分析显示,断裂能是反映钢纤维阻裂效应的敏感参数,用全息干涉条纹图的判识和用断裂能描述获得的试件断裂行为是一致的,激光实时全息干涉法能够为混凝土断裂力学研究提供可靠的试验支撑。 相似文献
8.
基于渐近展开法的脆性岩石双尺度方法初步研究 总被引：1，自引：0，他引：1
将渐近展开法与细观统计模型相结合,研究了脆性岩石双尺度计算方法。该方法在细观尺度定义材料属性,假定材料参数符合Weibull分布,采用弹性－理想脆性本构模型,脆断标准采用修正的Mohr-Coulomb准则和最大拉应力准则,通过宏细观尺度耦合计算,得到细观尺度材料损伤演化及其对结构宏观性状的影响。方法包括确定材料统计参数、确定细观尺度代表性体积单元（RVE）及求解边值方程等步骤。数值模型采用商业软件ABAQUS及其内嵌的UMAT用户子程序实现。该方法适用于岩石单轴受压或低围压应力状态,考虑到计算效率,计算时宜采用混合尺度,即模型重点（关键）部位采用双尺度,而其他区域采用单尺度计算。宏观尺度材料软化后未采用正则化方法,此时的计算结果有网格依赖性。 相似文献
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H. Y. Liu S. Q. Kou P.-A. Lindqvist C. A. Tang 《Rock Mechanics and Rock Engineering》2007,40(2):107-144
Summary A series of numerical tests including both rock mechanics and fracture mechanics tests are conducted by the rock and tool
(R–T2D) interaction code coupled with a heterogeneous masterial model to obtain the physical–mechanical properties and fracture
toughness, as well as to simulate the crack initiation and propagation, and the fracture progressive process. The simulated
results not only predict relatively accurate physical–mechanical parameters and fracture toughness, but also visually reproduce
the fracture progressive process compared with the experimental and theoretical results. The detailed stress distribution
and redistribution, crack nucleation and initiation, stable and unstable crack propagation, interaction and coalescence, and
corresponding load–displacement curves can be proposed as benchmarks for experimental study and theoretical research on crack
propagation. It is concluded that the heterogeneous material model is reasonable and the R–T2D code is stable, repeatable and a valuable numerical tool for research on the rock fracture process. 相似文献
10.
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
11.
Damage and fracture propagation around underground excavations are important issues in rock engineering. The analysis of quasi-brittle materials can be performed using constitutive laws based upon damage mechanics. The finite element code RFPA2D (Rock Failure Process Analysis) based on damage mechanics was used to simulate a loading-type failure process around an underground excavation (model tunnel) in brittle rock. One of the features of RFPA2D is the capability of modeling heterogeneous materials. In the current model, the effect of the homogeneous index (m) of rock on the failure modes of a model tunnel in rock was studied. In addition, by recording the number of damaged elements and the associated amount of energy released, RFPA2D is able to simulate acoustic activities around circular openings in rock. The results of a numerical simulation of a model tunnel were in very good agreement with the experimental test using the acoustic emission technique. Finally, the influence of the lateral confining pressure on the failure mechanism of the rock around the model tunnel was also investigated by numerical simulations. 相似文献
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This paper develops a practical approach to simulating fracture propagation in rock and concrete based on an augmented virtual internal bond (VIB) method in which the cohesion of solid is modeled as material particles interconnected by a network of randomized virtual micro bonds described by the Xu–Needleman potential. The micro bond potential is used to derive macroscale constitutive relations via the Cauchy–Born rule. By incorporating different energy contributions due to stretch and shearing, as well as different energy levels under tension and compression of each micro bond, the derived macro constitutive laws are particularly useful for modeling quasi‐brittle materials such as rock and concrete which usually have different Poisson ratios and much higher compressive strength than tensile strength. The mesh‐size sensitivity associated with strain‐softening in the present constitutive model is addressed by adjusting material constants near the crack tip so that the biJ‐integral is kept equal to the intrinsic fracture energy of the material. Numerical examples demonstrate that the proposed VIB method is capable of simulating mixed mode fracture propagation in rock and concrete with results in consistency with relevant experimental observations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
用三维梁-颗粒模型BPM3D(beam-particlemodelinthreedimensions)对岩石类非均质脆性材料的力学性质和破坏过程进行了数值模拟。梁-颗粒模型是在离散单元法基础上,结合有限单元法中的网格模型提出的用于模拟岩石类材料损伤破坏过程的数值模型。在模型中,材料在细观层次上被离散为颗粒单元集合体,相邻颗粒单元由有限单元法中的弹脆性梁单元联结。梁单元的力学性质均按韦伯(Weibull)分布随机赋值,以模拟岩石类材料力学参数的空间变异性。材料内部裂纹通过断开梁单元来模拟。通过自动生成的非均质材料模型对岩石类材料的破坏机理进行研究。岩石类非均质脆性材料在单轴压缩状态下破坏过程细观数值模拟结果显示,岩石材料宏观破坏是由于其内部细观裂纹产生、扩展、贯通的结果。通过数值模拟结果之间的对比分析,揭示出岩石试样宏观破坏模式随细观层次上韦伯分布参数的变化而不同。与实际矿柱破坏形态的对比分析表明了模型的适用性。根据数值模拟结果对岩石类非均质材料的破坏机理进行了探讨。 相似文献
14.
根据围压条件下的断裂力学理论 ,采用双翼裂纹厚壁圆筒 ,对泥岩进行了不同围压和不同泥质含量条件下的人工岩样断裂韧性测试。建立了有限元方法解释断裂韧性的数值模型。在进行大量实验测试的基础上 ,通过回归分析表明 ,断裂韧性与围压、泥质含量有较好的线性统计关系。解决了水力压裂设计中断裂韧性参数的准确获取问题 ,有利于提高压裂设计、预测的精度 相似文献
15.
A finite volume-based numerical modeling framework using a hierarchical fracture representation (HFR) has been developed to compute flow-induced shear failure. To accurately capture the mechanics near fracture manifolds, discontinuous basis functions are employed which ensure continuity of the displacement gradient across fractures. With these special basis functions, traction and compressive forces on the fracture segment can be calculated without any additional constraints, which is extremely useful for estimating the irreversible displacement along the fracture (slip) based on a constitutive friction law. The method is further extended to include slip-dependent hydraulic aperture change and grid convergent results are obtained. Further, the change in hydraulic aperture is modeled using an asymptotic representation which respects the experimentally observed behavior of pore volume dilation due to shear slip. The model allows the initial rapid increase in hydraulic aperture due to shear slip and asymptotically approaches a finite value after repeated shearing of a fracture segment. This aperture increase is the only feedback for mechanics into the fluid flow for a linear elastic mechanics problem. The same model is also extended to include poroelastic relations between flow and mechanics solver. The grid convergence result in the case of poroelastic flow-mechanics coupling for flow-induced shear failure is also obtained. This proves the robustness of the numerical and analytical modeling of fracture and friction in the extended finite volume method (XFVM) set-up. Finally, a grid convergent result for seismic moment magnitude for single fracture and fracture network with random initial hydraulic and friction properties is also obtained. The b-value, which represents the slope of seismic moment occurrence frequency decay vs seismic moment magnitude, which is approximately constant in a semi-logarithmic plot, is estimated. The numerical method leads to converged b-values for both single fracture and fracture network simulations, as grid and time resolutions are increased. For the resulting linear system, a sequential approach is used, that is, first, the flow and then the mechanics problems are solved. The new modeling framework is very useful to predict seismicity, permeability, and flow evolution in geological reservoirs. This is demonstrated with numerical simulations of enhancing a geothermal system. 相似文献
16.
《Journal of Structural Geology》1999,21(8-9):1049-1055
One model for the development of hybrid shear fractures is transitional–tensile fracture propagation, a process described as the in-plane propagation of a crack subject to a shear traction while held open by a tensile normal stress. Presumably, such propagation leads to a brittle structure that is the hybrid of a joint and a shear fracture. Crack–seal veins with oblique fibers are possible candidates. While these veins clearly show shear offset, this is not conclusive evidence that a shear traction was present at the time of initial crack propagation. Many recent structural geology textbooks use a parabolic Coulomb–Mohr failure envelope to explain the mechanics of transitional–tensile fracturing. However, the laboratory experiments cited as demonstrating transitional–tensile behavior fail to produce the fracture orientation predicted by a parabolic failure envelope. Additional attempts at verification include field examples of conjugate joint sets with small acute angles, but these conjugate joints form neither simultaneously nor in the stress field required by the transitional–tensile model. Finally, linear elastic fracture mechanics provides strong theoretical grounds for rejecting the notion that individual cracks propagate in their own plane when subject to a shear traction. These observations suggest that transitional–tensile fracture propagation is unlikely to occur in homogeneous, isotropic rock, and that it is not explained by a parabolic Coulomb–Mohr failure envelope as several recent structural geology textbooks have suggested. 相似文献
17.
H. M. Doghozlou M. Goodarzi H. Rafiei Renani E. F. Salmi 《Environmental Earth Sciences》2016,75(23):1478
The expansion of the Neyriz marble mine into deeper levels caused an unexpected failure particularly in the toes of lower benches. This phenomenon can impact the overall stability of the quarry and results in undesirable environmental and technical consequences. To understand the failure mechanism, a comprehensive study including—laboratory testing, in situ field testing and theoretical analyses are carried out. The theory of the brittle failure which was mainly developed based on the experiences gained during excavation in granite rocks is adopted and augmented in this study to explain the governing mechanism of failure. Mechanical properties of the marble are determined using conventional rock mechanics tests, and the in situ stress field was evaluated using a modified under coring test. Analyzing the laboratory and field data with the available empirical criteria for brittle failure shows that the level of stress in the lower bench is high enough to initiate the brittle failure. Finally, constitutive models developed for this failure mode are adopted in conjunction with numerical modeling to investigate the observed failure in the quarry. Two modeling strategies, based on elastic and elastic–plastic analyses, are considered. Comparing the predicted failure surface with the observed failure profile, it can be concluded that the brittle failure criteria can very well capture the failure mechanism in this marble quarry. This shows that the criteria proposed to describe spalling failure around underground excavation in granite can be effectively employed for assessing the brittle failure in deep open cast and quarry mines in good quality rocks such as marble. 相似文献
18.
Particle-tracking simulation offers a fast and robust alternative to conventional numerical discretization techniques for modeling solute transport in subsurface formations. A common challenge is that the modeling scale is typically much larger than the volume scale over which measurements of rock properties are made, and the scale-up of measurements have to be made accounting for the pattern of spatial heterogeneity exhibited at different scales. In this paper, a statistical scale-up procedure developed in our previous work is adopted to estimate coarse-scale (effective) transition time functions for transport modeling, while two significant improvements are proposed: considering the effects of non-stationarity (trend), as well as unresolved (residual) heterogeneity below the fine-scale model. Rock property is modeled as a multivariate random function, which is decomposed into the sum of a trend (which is defined at the same resolution of the transport modeling scale) and a residual (representing all heterogeneities below the transport modeling scale). To construct realizations of a given rock property at the transport modeling scale, multiple realizations of the residual components are sampled. Next, a flow-based technique is adopted to compute the effective transport parameters: firstly, it is assumed that additional unresolved heterogeneities occurring below the fine scale can be described by a probabilistic transit time distribution; secondly, multiple realizations of the rock property, with the same physical size as the transport modeling scale, are generated; thirdly, each realization is subjected to particle-tracking simulation; finally, probability distributions of effective transition time function are estimated by matching the corresponding effluent history for each realization with an equivalent medium consisting of averaged homogeneous rock properties and aggregating results from all realizations. The proposed method is flexible that it does not invoke any explicit assumption regarding the multivariate distribution of the heterogeneity. 相似文献
19.
The Time-Dependent Reduction of Sliding Cohesion due to Rock Bridges Along Discontinuities: A Fracture Mechanics Approach 总被引：1，自引：3，他引：1
J. Kemeny 《Rock Mechanics and Rock Engineering》2003,36(1):27-38
Summary
In this paper, a fracture mechanics model is developed to illustrate the importance of time-dependence for brittle fractured
rock. In particular a model is developed for the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion
is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics
model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function
of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found
to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value
that results in slope instability. A second example is given where variations in some of the material parameters are assumed.
A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability
of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples
show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for
relatively short-term rock structures.
Received November 5, 2001; accepted July 24, 2002; Published online November 19, 2002 相似文献