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在FLAC-3D软件平台上,开发出岩石破裂过程的渗流-损伤耦合分析程序,对渗流-损伤耦合作用下岩石的裂纹萌生、扩展过程进行模拟研究。分析了在孔隙水压力作用下,含原生裂隙和弱化单元的非均质试件在单轴、三轴加载下的破坏过程,并与非渗流条件下试件在单轴、三轴压缩下的破坏过程相对比,通过动态显示损伤状态、渗流场,并分析应力应变关系、位移图等,对渗流影响下裂隙岩体的损伤和渐进破裂过程进行了研究。 相似文献
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高水压下岩体裂纹扩展的渗流-断裂耦合机制与数值实现 总被引：1，自引：0，他引：1
采用渗流力学、断裂力学理论结合Monte Carlo方法描述岩体裂纹的随机分布,研究高水压作用下岩体原生裂纹的变形和翼形裂纹的萌生、扩展、贯通的渗流-断裂耦合作用机制,建立高水压作用下岩体裂纹的渗流-断裂耦合数学模型,给出该数学模型的求解策略与方法,在Fortran95平台下开发高水压下岩体裂纹扩展的渗流-断裂耦合分析程序HWFSC.for。高水压下岩体裂纹扩展的渗流-断裂耦合体现在岩体裂纹网络和渗流初始条件都随渗流时步变化。对高压注水岩体裂纹扩展过程进行渗流-断裂耦合分析。结果表明,高压注水条件下,岩体裂纹扩展存在起动水压力,当水压力大于起动水压力时,裂纹尖端开始萌生翼形裂纹,随着裂纹水压力的增加,翼形裂纹扩展,进而与其他裂纹搭接贯通,停止扩展。渗流-断裂耦合分析考虑了裂纹动、静水压力对裂纹产生的法向扩张效应及翼形裂纹的扩展而形成新的渗流通道两方面的影响,连通裂纹数随渗流的发展而增加。岩体裂纹的渗流-断裂耦合分析,能较真实地再现岩体裂纹的水力劈裂现象,描述岩体裂纹的扩展、贯通过程及与之相耦合的渗流响应。 相似文献
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《岩土力学》2019,(11)
采用最新配置的水泥砂浆材料,通过在试件中布置倾斜裂隙和水平裂隙,开展了单轴和双轴条件下的压缩试验,详细分析了不同加载条件下试件裂隙的扩展和贯通规律。试验结果表明:无裂隙内水压时,在单轴压缩条件下倾斜裂隙在扩展贯通水平裂隙后裂纹的扩展路径和方向发生明显改变,试样最终发生劈裂破坏。侧压的增大抑制了倾斜裂隙端部翼裂纹和次生裂纹的萌生,高侧压下翼裂纹没有贯穿水平裂隙,试样破坏模式变成了剪切破坏。水力耦合作用下,单轴压缩时倾斜裂隙翼裂纹尖端的最大主应力分布范围随着内水压的增大逐渐变小,翼裂纹的起裂应力、起裂角和峰值强度逐渐降低,试样发生劈裂破坏。通过数值模拟得到的裂纹扩展贯通规律与试验结果具有良好的一致性,开展了不同内水压时倾斜裂隙扩展贯通无水压的水平裂隙的数值分析,随着内水压的增加倾斜裂隙首先萌生共面裂纹随后产生翼裂纹,翼裂纹扩展贯通水平裂隙时扩展路径同样会发生改变。水力耦合作用下侧压也会抑制翼裂纹的萌生,随着内水压的增大减弱了侧压对倾斜裂隙翼裂纹的抑制作用。 相似文献
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为了研究岩石在水力耦合作用下的启裂机制,针对溪洛渡玄武岩开展了水力耦合三轴试验与声发射测试。试验结果表明：玄武岩峰值强度随着围压的增大而增大,表现出典型的硬脆性行为;当围压保持不变时,其峰值强度随初始水压增大而逐渐降低,同时硬脆性减弱。声发射测试结果表明：玄武岩在水力耦合作用下的裂纹启裂为张拉破坏,在裂纹稳定扩展阶段以张拉破坏为主,以剪切破坏为辅,且这些破坏均主要发生在岩石中部;在裂纹非稳定扩展的峰后阶段,岩石破裂以剪切破坏为主。在玄武岩启裂机制认识的基础上,基于单一圆孔理论推导得到水力耦合条件下岩石裂纹启裂的临界水压破坏准则,并将其引入玄武岩水力耦合三轴试验数值仿真,分析了玄武岩水力耦合破坏过程与水压分布规律,验证了临界水压破坏准则的合理性,对于水力耦合作用下岩石破坏过程研究具有较好的参考价值。 相似文献
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考虑岩石介质的非均匀性,把爆破过程视为爆炸应力波和爆生气体压力共同作用的结果,基于损伤力学理论建立了岩石爆破的力学模型,并对不同地应力条件下岩石双孔爆破裂纹演化规律进行了数值模拟,分析了不同侧压力系数和埋 深对裂纹扩展规律的影响。数值模拟结果表明：①爆炸应力波导致裂纹的萌生,爆生气体压力则会使裂纹进一步扩展和贯通; ②裂纹演化过程与地应力密切相关,裂纹扩展的主方向趋于最大地应力方向;③随着埋深增加和初始地应力增大,裂纹扩展半径和裂纹区面积减小,地应力对爆破致裂的抑制作用明显。 相似文献
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岩体裂纹的水力劈裂是岩体开裂渗漏甚至施工涌水的重要影响因素之一,也是岩土工程界的研究热点。从断裂力学角度分析了爆破开挖对岩体含水裂纹扩展的扰动作用,结果表明,爆破开挖扰动下,岩体含水裂纹的扩展,与爆炸应力波强度及其入射角、地应力的大小与方向、孔隙水压大小、裂纹的倾角及断裂韧度等因素相关;爆炸应力波的作用,相当于增大了岩体裂纹中的孔隙水压力,每1 cm/s的峰值振动速度相当于增大100 kPa的孔隙水压力,爆破振动速度越大,所产生的爆破扰动荷载越大;岩体开挖引起的岩体裂纹近区地应力及其孔隙水压力的变化,对裂纹的失稳与扩展具有较复杂的影响,可改变裂纹的失稳扩展模式。 相似文献
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模拟岩石压剪状态下主次裂纹萌生开裂的扩展有限元法 总被引：1，自引：0，他引：1
压剪应力状态下,岩石类材料中常见两类裂纹：翼型张拉裂纹和次生压剪裂纹。基于扩展有限元方法（XFEM）,提出了模拟压剪裂纹面作用机制的扩展有限元位移增强方案,并给出了扩展有限元法分叉裂纹处理方法,分别用最大周向拉应力准则和Mohr-Coulomb准则判断张拉裂纹和压剪裂纹的萌生和扩展。基于Matlab平台编写了数值计算程序Betaxfem 2D,通过两个算例对所提方案进行了验证,所得结果与有限元法（FEM）计算结果吻合很好。模拟了单轴压缩载荷下含预制闭合裂纹试件的裂纹分叉、扩展过程,与试验结果的对比表明,所提方案可以模拟和预测岩石类材料张拉、压剪交互分叉裂纹的萌生和扩展行为。 相似文献
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为研究水力耦合作用下砂岩裂纹扩展特征,开展了不同孔隙水压和围压条件的砂岩破坏试验。结果表明：有效围压相同,随着孔隙水压力增大,脆性指标数增大,起裂应力、损伤应力和峰值应力都变小;裂纹初始体积应变变小,裂纹扩展体积应变先减小后增大,损伤应力与峰值应力对应的裂纹轴向应变扩展速率、裂纹环向应变扩展速率增加,裂纹体积应变扩展速率与孔隙水压力关系不明显。孔隙水压力相同,随着有效围压增加,起裂应力、损伤应力和峰值应力增大。起裂应力、损伤应力、峰值应力对应的裂纹轴向应变扩展速率、裂纹环向应变扩展速率和裂纹体积应变扩展速率增大。同一块砂岩特征应力点的裂纹应变扩展速率比较,裂纹轴向应变扩展速率最大,裂纹环向应变扩展速率次之,裂纹体积应变扩展速率最小。 相似文献
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S. Y. Wang S. W. Sloan S. G. Fityus D. V. Griffiths C. A. Tang 《Rock Mechanics and Rock Engineering》2013,46(5):1165-1182
Rock is a heterogeneous geological material. When rock is subjected to internal hydraulic pressure and external mechanical loading, the fluid flow properties will be altered by closing, opening, or other interaction of pre-existing weaknesses or by induced new fractures. Meanwhile, the pore pressure can influence the fracture behavior on both a local and global scale. A finite element model that can consider the coupled effects of seepage, damage and stress field in heterogeneous rock is described. First, two series of numerical tests in relatively homogeneous and heterogeneous rocks were performed to investigate the influence of pore pressure magnitude and gradient on initiation and propagation of tensile fractures. Second, to examine the initiation of hydraulic fractures and their subsequent propagation, a series of numerical simulations of the behavior of two injection holes inside a saturated rock mass are carried out. The rock is subjected to different initial in situ stress ratios and to an internal injection (pore) pressure at the two injection holes. Numerically, simulated results indicate that tensile fracture is strongly influenced by both pore pressure magnitude and pore pressure gradient. In addition, the heterogeneity of rock, the initial in situ stress ratio (K), the distance between two injection holes, and the difference of the pore pressure in the two injection holes all play important roles in the initiation and propagation of hydraulic fractures. At relatively close spacing and when the two principal stresses are of similar magnitude, the proximity of adjacent injection holes can cause fracturing to occur in a direction perpendicular to the maximum principal stress. 相似文献
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裂隙是油气储层主要的储集空间及流体渗流通道,影响油气的运移规律,是油气勘探开发的重要指标。以冀中坳陷任丘油田任10井为例,运用数值模拟方法研究了裂隙开展宽度和裂隙面粗糙度对岩石渗流特性的影响规律。研究结果表明,(1)裂隙开展宽度较小时,孔隙内流体压力仅在入口处小范围内呈扇形分布,裂隙中压力分布曲线呈正切函数型,流体流速在裂隙和孔隙中都较小;随着裂缝开展宽度的增加,孔隙内流体压力逐渐增大,裂隙中压力分布曲线逐渐向直线型转变,流体流速在入口处先减小后稳定,在裂隙中先增加后稳定;(2)裂隙面粗糙度对裂隙岩石渗流特性的影响与裂隙开展宽度有关,在裂隙开展宽度较大时,裂隙面粗糙度对流体压力的分布影响较大;随着裂隙面粗糙度增大,孔隙内流速逐渐增大,而裂隙中流速逐渐减小;(3)随着裂隙开展宽度的增大,影响裂隙流体流动的主控因素逐渐由裂隙开展宽度转变为裂隙面粗糙度。 相似文献
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In this article, we investigate the main parameters that influence the propagation of a fluid‐driven fracture in a poroelastoplastic continuum. These parameters include the cohesive zone, the stress anisotropy, and the pore pressure field. The fracture is driven in a permeable porous domain that corresponds to weak formation by pumping of an incompressible viscous fluid at the fracture inlet under plane strain conditions. Rock deformation is modeled with the Mohr–Coulomb yield criterion with associative flow rule. Fluid flow in the fracture is modeled by the lubrication theory. The movement of the pore fluid in the surrounding medium is assumed to obey the Darcy law and is of the same nature as the fracturing fluid. The cohesive zone approach is used as the fracture propagation criterion. The problem is modeled numerically with the finite element method to obtain the solution for the fracture length, the fracture opening, and the propagation pressure as a function of the time and distance from the pumping inlet. It is demonstrated that the plastic yielding that is associated with the rock dilation in an elastoplastic saturated porous continuum is significantly affected by the cohesive zone characteristics, the stress anisotropy, and the pore pressure field. These influences result in larger fracture profiles and propagation pressures due to the larger plastic zones that are developing during the fracture propagation. Furthermore, it is also found that the diffusion process that is a major mechanism in hydraulic fracture operations influences further the obtained results on the fracture dimensions, plastic yielding, and fluid pressures. These findings may explain partially the discrepancies in net pressures between field measurements and conventional model predictions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Yongquan Hu Zhiqiang Li Jinzhou Zhao Zhengwu Tao Pan Gao 《Environmental Earth Sciences》2017,76(15):546
The ultra-low-permeability shale gas reservoir has a lot of well-developed natural fractures. It has been proven that hydraulic fracture growth pattern is usually a complex network fracture rather than conventional single planar fractures by micro-seismic monitoring, which can be explained as the shear and tensile failure of natural fractures or creation of new cracks due to the increase in reservoir pore pressure caused by fluid injection during the process of hydraulic fracturing. In order to simulate the network fracture growth, a mathematical model was established based on full tensor permeability, continuum method and fluid mass conservation equation. Firstly, the governing equation of fluid diffusivity based on permeability tensor was solved to obtain the reservoir pressure distribution. Then Mohr–Coulomb shear failure criterion and tensile failure criterion were used to decide whether the rock failed or not in any block on the basis of the calculated reservoir pressure. The grid-block permeability was modified according to the change of fracture aperture once any type of rock failure criterion was met within a grid block. Finally, the stimulated reservoir volume (SRV) zone was represented by an enhancement permeability zone. After calibrating the numerical solution of the model with the field micro-seismic information, a sensitivity study was performed to analyze the effects of some factors including initial reservoir pressure, injection fluid volume, natural fracture azimuth angle and horizontal stress difference on the SRV (shape, size, bandwidth and length). The results show that the SRV size increases with the increasing initial pore reservoir and injection fluid volume, but decreases with the increase in the horizontal principal stress difference and natural fracture azimuth angle. The SRV shape is always similar for different initial pore reservoir and injection fluid volume. The SRV is observed to become shorter in length and wider in bandwidth with the decrease in natural fracture azimuth angle and horizontal principal stress difference. 相似文献
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Carbon dioxide injection and associated hydraulic fracturing of reservoir formations 总被引：2，自引：1，他引：1
The storage potential of subsurface geological systems makes them viable candidates for long-term disposal of significant quantities of CO2. The geo-mechanical responses of these systems as a result of injection processes as well as the protracted storage of CO2 are aspects that require sufficient understanding. A hypothetical model has been developed that conceptualises a typical well-reservoir system comprising an injection well where the fluid (CO2) is introduced and a production/abandoned well sited at a distant location. This was accomplished by adopting a numerical methodology (discrete element method), specifically designed to investigate the geo-mechanical phenomena whereby the various processes are monitored at the inter-particle scale. Fracturing events were simulated. In addition, the influence of certain operating variables such as injection flow rate and fluid pressure was studied with particular interest in the nature of occurring fractures and trend of propagation, the pattern and magnitude of pressure build-up at the well vicinity, pressure distribution between well regions and pore velocity distribution between well regions. Modelling results generally show an initiation of fracturing caused by tensile failure of the rock material at the region of fluid injection; however, fracturing caused by shear failure becomes more dominant at the later stage of injection. Furthermore, isolated fracturing events were observed to occur at the production/abandoned wells that were not propagated from the injection point. This highlights the potential of CO2 introduced through an injection well, which could be used to enhance oil/gas recovery at a distant production well. The rate and magnitude of fracture development are directly influenced by the fluid injection rate. Likewise, the magnitude of pressure build-up is greatly affected by the fluid injection rate and the distance from the point of injection. The DEM modelling technique illustrated provides an effective procedure that allows for more specific investigations of geo-mechanical mechanisms occurring at subsurface systems. The application of this methodology to the injection and storage of CO2 facilitates the understanding of the fracturing phenomenon as well as the various factors governing the process. 相似文献
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This paper presents the development of a discrete fracture model of fully coupled compressible fluid flow, adsorption and geomechanics to investigate the dynamic behaviour of fractures in coal. The model is applied in the study of geological carbon dioxide sequestration and differs from the dual porosity model developed in our previous work, with fractures now represented explicitly using lower-dimensional interface elements. The model consists of the fracture-matrix fluid transport model, the matrix deformation model and the stress-strain model for fracture deformation. A sequential implicit numerical method based on Galerkin finite element is employed to numerically solve the coupled governing equations, and verification is completed using published solutions as benchmarks. To explore the dynamic behaviour of fractures for understanding the process of carbon sequestration in coal, the model is used to investigate the effects of gas injection pressure and composition, adsorption and matrix permeability on the dynamic behaviour of fractures. The numerical results indicate that injecting nonadsorbing gas causes a monotonic increase in fracture aperture; however, the evolution of fracture aperture due to gas adsorption is complex due to the swelling-induced transition from local swelling to macro swelling. The change of fracture aperture is mainly controlled by the normal stress acting on the fracture surface. The fracture aperture initially increases for smaller matrix permeability and then declines after reaching a maximum value. When the local swelling becomes global, fracture aperture starts to rebound. However, when the matrix permeability is larger, the fracture aperture decreases before recovering to a higher value and remaining constant. Gas mixtures containing more carbon dioxide lead to larger closure of fracture aperture compared with those containing more nitrogen. 相似文献
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A numerical model is developed for investigating the evolution of fracture permeability in a coupled fracture-matrix system in the presence of fracture-skin with simultaneous colloidal and bacterial tr... 相似文献
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The details of the Element Free Galerkin (EFG) method are presented with the method being applied to a study on hydraulic fracturing initiation and propagation process in a saturated porous medium using coupled hydro-mechanical numerical modelling. In this EFG method, interpolation (approximation) is based on nodes without using elements and hence an arbitrary discrete fracture path can be modelled.The numerical approach is based upon solving two governing partial differential equations of equilibrium and continuity of pore water simultaneously. Displacement increment and pore water pressure increment are discretized using the same EFG shape functions. An incremental constrained Galerkin weak form is used to create the discrete system of equations and a fully implicit scheme is used for discretization in the time domain. Implementation of essential boundary conditions is based on the penalty method. In order to model discrete fractures, the so-called diffraction method is used.Examples are presented and the results are compared to some closed-form solutions and FEM approximations in order to demonstrate the validity of the developed model and its capabilities. The model is able to take the anisotropy and inhomogeneity of the material into account. The applicability of the model is examined by simulating hydraulic fracture initiation and propagation process from a borehole by injection of fluid. The maximum tensile strength criterion and Mohr–Coulomb shear criterion are used for modelling tensile and shear fracture, respectively. The model successfully simulates the leak-off of fluid from the fracture into the surrounding material. The results indicate the importance of pore fluid pressure in the initiation and propagation pattern of fracture in saturated soils. 相似文献
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Field injectivity tests are widely used in the oil and gas industry to obtain key formation characteristics. The prevailing approaches for injectivity test interpretation rely on traditional analytical models. A number of parameters may affect the test results and lead to interpretation difficulties. Understanding their impacts on pressure response and fracture geometry of the test is essential for accurate test interpretation. In this work, a coupled flow and geomechanics model is developed for numerical simulation of field injectivity tests. The coupled model combines a cohesive zone model for simulating fluid-driven fracture and a poro-elastic/plastic model for simulating formation behavior. The model can capture fracture propagation, fluid flow within the fracture and formation, deformation of the formation, and evolution of pore pressure and stress around the wellbore and fracture during the tests. Numerical simulations are carried out to investigate the impacts of a multitude of parameters on test behaviors. The parameters include rock permeability, the leak-off coefficient of the fracture, rock stiffness, rock toughness, rock strength, plasticity deformation, and injection rate. The sensitivity of pressure response and fracture geometry on each parameter is reported and discussed. The coupled flow and geomechanics model provides additional advantages in the understanding of the fundamental mechanisms of field injectivity tests. 相似文献
20.
Two-dimensional hydraulic fracturing simulations using the cohesive zone model (CZM) can be readily found in the literature; however, to our knowledge, verified 3D cohesive zone modeling is not available. We present the development of a 3D fully coupled hydro-mechanical finite element method (FEM) model (with parallel computation framework) and its application to hydraulic fracturing. A special zero-thickness interface element based on the CZM is developed for modeling fracture propagation and fluid flow. A local traction-separation law with strain softening is used to capture tensile cracking. The model is verified by considering penny-shaped hydraulic fracture and plain strain Kristianovich‑Geertsma‑de Klerk hydraulic fracture (in 3D) in the viscosity- and toughness-dominated regimes. Good agreement between numerical results and analytical solutions has been achieved. The model is used to investigate the influence of rock and fluid properties on hydraulic fracturing. Lower stiffness tip cohesive elements tend to yield a larger elastic deformation around the fracture tips before the tensile strength is reached, generating a larger fracture length and lower fracture pressure compared with higher stiffness elements. It is found that the energy release rate has almost no influence on hydraulic fracturing in the viscosity-dominated regime because the energy spent in creating new fractures is too small when compared with the total input energy. For the toughness-dominated regime, the released energy during fracturing should be accurately captured; relatively large tensile strength should be used in order to match numerical results to the asymptotic analytical solutions. It requires smaller elements when compared with those used in the viscosity-dominated regime. 相似文献