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1.
Trullenque Ghislain Parashar Rishi Delcourt Clément Collet Lucille Villard Pauline Potel Sébastien 《Hydrogeology Journal》2017,25(3):813-827
Results of a series of deformation experiments conducted on gabbro samples and numerical models for computation of flow are presented. Rocks were subjected to triaxial tests (σ1 > σ2 = σ3) under σ3 = 150 MPa confining pressure at room temperature, to generate fracture network patterns. These patterns were either produced by keeping a constant confining pressure and loading the sample up to failure (conventional test: CT), or by building up a high differential stress and suddenly releasing the confining pressure (confining pressure release test: CPR). The networks are similar in overall density but differ primarily in the orientation of smaller fractures. In the case of CT tests, a conjugate fracture set is observed with one dominant fracture zone running at about 20° from σ1. CPR tests do not show such a conjugate pattern and the mean fracture orientation is at around 35° from σ1. Discrete fracture network (DFN) methodology was used to determine the distribution of flow and hydraulic head for both fracture sets under simple boundary conditions and uniform transmissivity values. The fracture network generated by CT and CPR tests exhibit different patterns of flow field and hydraulic head configurations, but convey approximately the same amount of flow at all scales for which DFN models were simulated. The numerical modelling results help to develop understanding of qualitative differences in flow distribution that may arise in rocks of the same mineralogical composition and mechanical properties, but under the influence of different stress conditions, albeit at similar overall stress magnitude.
相似文献2.
从细观角度出发,研究各细观参数对黄土三轴试验宏观力学响应的影响,基于三维离散元PFC3D软件及理论,结合室内三轴试验结果确定数值模拟基本细观参数取值范围,在50 kPa、100 kPa、150 kPa、200 kPa围压下对三轴试样进行颗粒流模拟,通过改变各细观参数值对黄土数值试样宏观力学行为影响程度及正交试验设计的方式,开展黄土三轴数值模拟过程中摩擦系数、孔隙率、颗粒刚度比kn/ks、颗粒粒径分布的敏感性分析,建立土体细观参数与宏观力学的关系式。结果表明:不同围压下数值试样峰值强度和剩余强度均与摩擦系数正相关,与颗粒刚度比、孔隙率负相关,而颗粒粒径分布的变化对其影响均小于2%。低围压下(50 kPa),孔隙率对数值试样峰值抗剪强度和剩余强度影响最大,颗粒刚度比次之,高围压下(200 kPa),摩擦系数对数值试样强度的影响比颗粒刚度比更为显著;对数值试样的初始线弹性模量和应变软化特性影响最大的细观参数为孔隙率,刚度比次之,颗粒粒径分布最小,200 kPa围压下正交试验分析结果与数值分析结果一致。通过改变细观参数取值范围的方式系统地分析了其对黄土三轴试验宏观力学性能的影响,为今后离散元软件用于黄土室内试验研究提供了参考。 相似文献
3.
通过采用传统的岩石薄片显微鉴定和现代化扫描、透视电子显微镜、X射线衍射分析、差热分析等方法对9煤至奥灰间隔水层岩石的结构、构造、矿物成分进行了综合测试，微观研究表明，区内9煤至奥灰问地层中铝含量较高，隔水层中泥质岩粘土矿物主要以叶腊石、伊利石、高岭石为主，大部分岩石遇水后稳定，无崩解现象。其中在煤系地层中发现大量叶腊石。初步分析认为是受后期强烈岩浆岩活动影响，发生热液蚀变而形成。通过压汞实验测试了10个隔水层岩样空隙结构，原岩状态下，9煤至奥灰含水层间隔水层空隙度很低，呈现致密状态，因而应具有良好的隔水能力。 相似文献
4.
为探究不同外部环境因素影响下浅层粉砂质泥岩边坡裂隙渗流特性,采用自主研发的岩体裂隙渗流试验装置,对含6种不同裂隙面粗糙度（JRC）的粉砂质泥岩裂隙试样进行渗流试验,研究了不同低围压和覆水深度下粉砂质泥岩裂隙渗流特性。结果表明：不同覆水深度及JRC下围压与粉砂质泥岩裂隙渗透系数均呈反相关,两者之间关系可用幂函数表征,且渗透系数的降低过程可分为快速降低（围压为0～30 kPa）和缓慢降低（围压为30～50 kPa）两个阶段,CT扫描结果验证了围压增大使得粉砂质泥岩裂隙开度减小是渗透系数随围压增大而减小的主要原因。随围压的增大或覆水深度的减小,不同JRC粉砂质泥岩裂隙渗透系数的离散程度逐渐减小。当围压增至最大,同时覆水深度最小时,JRC对裂隙渗透系数的影响将会被消除。不同围压下,粉砂质泥岩裂隙渗透系数与覆水深度呈正相关,且两者关系可用指数函数表征。推导出了粉砂质泥岩裂隙渗流非线性Izabsh模型,该模型能较好地反映低应力及低流速下粉砂质泥岩裂隙渗流量与压力梯度之间的非线性变化关系,但随围压的增大,该模型的相关性有一定程度的减小。 相似文献
5.
为研究储层微观孔隙结构和建立微观渗流模型,本文通过对东营凹陷沙三中亚段H152井区的典型低渗透储层岩样进行CT（computed tomography）扫描及图像处理,建立了微观尺度的数字岩心模型;继而经过对该模型进行分析和计算,提取了储层孔喉网络模型,在三维空间上直观、清晰地显示了不同尺度的孔隙及喉道的形态、大小和分布;最后通过对孔隙结构特征、孔隙度、渗透率和压降等动静态参数的分析和计算,建立了储层岩样的微观渗流模型。根据算法对比和参数分析结果认为：与传统中值滤波相比,非局部均值滤波算法可在相似性比较的基础上进行滤波处理,从而提高模型的准确性;基于CT的数字岩心建模可为地质研究提供可靠的数字模型;根据近似等压面假设的微观渗流数值模拟分析了流体渗流特征,为揭示低渗透储层流体渗流规律提供了一种新的途径。 相似文献
6.
Two-dimensional reactive transport modeling of the Maqarin Eastern Springs site, a natural analogue for the alteration of a fractured limestone by high-pH Portland cement waters, has been performed using the CrunchFlow code. These 2D calculations included transport by advection–dispersion–diffusion along a single fracture and diffusion in the wall rock. Solute transport was coupled to mineral dissolution and precipitation. A limited sensitivity analysis evaluated the effect of different values of primary mineral surface areas, flow velocity and sulfate concentration of the inflowing high-pH solution.Major secondary minerals include ettringite–thaumasite, C–S–H/C–A–S–H and calcite. C–S–H/C–A–S–H precipitation is controlled by the dissolution of primary silicates. Ettringite precipitation is controlled by diffusion of sulfate and aluminum from the wall rock to the fracture, with aluminum provided by the dissolution of albite. Calcite precipitation is controlled by diffusion of carbonate from the wall rock. Extents of porosity sealing along the fracture and in the fracture-wall rock interface depend on assumptions regarding flow velocity and composition of the high-pH solution. The multiple episodes of fracture sealing and reactivation evidenced in the fracture infills were not included in the simulations. Results can qualitatively reproduce the reported decrease in porosity in the fractures and in the wall rock next to the fractures. Instances of porosity increase next to fractures caused by carbonate dissolution were not reproduced by the calculations. 相似文献
7.
揭示致密砂岩的破裂机制对致密油气储层压裂设计和压裂缝网改造具有重要的指导意义。本文采用鄂尔多斯盆地延长组长6储层致密砂岩试样,开展了不同围压下的常规三轴压缩试验,分析了围压对岩石力学性质的影响。采用声发射定位技术研究了试样破裂过程,分析了不同围压下声发射定位事件的信号特征及其时空演化序列。此外,对破裂后试样进行了CT扫描,基于CT切片图像观测了试样内部破裂特征。得到以下几点认识:（1）不同围压下,声发射时空演化差异主要表现在压密阶段。随着围压的增加,声发射事件主要发生时段后移。（2）围压对声发射特征参数累计振铃计数的影响主要表现在压密阶段,其他阶段累计振铃计数呈相似变化趋势。不同围压下均可将累计振铃计数快速增加的瞬间作为岩石即将破裂的标志。（3）随着围压的增加,岩石破裂形态趋于简单化,由拉张破裂为主的复杂形态逐渐转变为单一的剪切破裂形态。（4）CT扫描切片直观地反映了试样的破裂形态,与声发射定位所得试样整体破裂形态相吻合,并且在声发射定位的基础上进一步刻画了裂纹分布情况与各裂纹相互作用过程。采用声发射定位技术与CT扫描双重方法,研究试样破裂过程,对于深入研究岩石破裂机制具有一定的意义。 相似文献
8.
Abigail L. Langston Gregory E. Tucker Robert S. Anderson Suzanne P. Anderson 《Applied Geochemistry》2011
Understanding the relationship between subsurface flow paths on hillslopes and chemical weathering of bedrock is fundamental to understanding the timing and mechanisms that weather bedrock to saprolite. The link between chemical weathering of bedrock and contact time with reactive water along flow paths motivates this study. Water drives the chemical alteration of rock into saprolite, yet connected porosity generally declines with depth into the weathered profile. Saprolite formation, therefore, reflects coupled weathering and permeability development over time. This study uses numerical modeling and soil-moisture monitoring to explore the hydrology of the unsaturated zone and the influence of fracture density, hillslope gradient, and permeability contrasts within the saprolite development horizon on saprolite development. 相似文献
9.
三重介质储渗系统与水驱油机理探讨——以塔河油田为例 总被引：8，自引：4，他引：8
探讨了塔河油田奥陶系碳酸盐岩油藏三重介质储渗系统的识别，划分和与之相对应的水驱油机理，具有高孔低渗特征的岩块系统主要靠自吸排油方式水驱油，在驱替压力和重力作用下，高孔高渗特征的洞穴系统水驱油近乎均匀推进，低孔高渗特征的裂缝系统水驱油易发生指进和突进。 相似文献
10.
基于泥质粉砂岩室内双轴压缩试验，建立PFC2D颗粒流数值模型，以此来探究泥质粉砂岩破坏的细观机理。考虑组成泥质粉砂岩试样的颗粒形状，根据电镜扫描图勾选出5种典型颗粒形状，与圆形颗粒一起生成给定孔隙率的稳定数值试样。颗粒间选用平行粘结接触模型，选取弹性模量、泊松比、峰值应力分别对饱和、天然状态的泥质粉砂岩试样进行不同围压下的细观参数标定，然后进行双轴压缩试验模拟，分析试样在双轴压缩试验过程中颗粒法向接触力、切向接触力、配位数、孔隙率等细观组构参数的分布特征和演化规律。试验结果表明:双轴压缩试验的细观参数标定可不考虑抗剪强度指标黏聚力c和内摩擦角ϕ值的影响。破坏前后，试样各方向统计范围内都存在法向接触力和切向接触力。围压的存在影响试样的起始配位数、孔隙率和试样破坏后的稳定配位数和孔隙率，对配位数和孔隙率的改变速率影响很小。试样空间孔隙率的演化在一定程度上反映了试样破坏时内部结构的变迁，能更加直观地反映试样的破坏模式。 相似文献
11.
Selected gas pulse tests on initially saturated claystone samples under isotropic confinement pressure are simulated using a 3D thermo‐hydro‐mechanical code. The constitutive model considers the hydro‐mechanical anisotropy of argillaceous rocks. A cross‐anisotropic linear elastic law is adopted for the mechanical behaviour. Elements for a proper modelling of gas flow along preferential paths include an embedded fracture permeability model. Rock permeability and its retention curve depend on strains through a fracture aperture. The hydraulic and mechanical behaviours have a common anisotropic structure. Small‐scale heterogeneity is considered to enhance the initiation of flow through preferential paths, following the direction of the bedding planes. The numerical simulations were performed considering two different bedding orientations, parallel and normal to the imposed flow in the test. Simulations are in agreement with recorded upstream and downstream pressures in the tests. The evolution of fluid pressures, degree of saturation, element permeability and stress paths are presented for each case analysed. This information provides a good insight into the mechanisms of gas transport. Different flow patterns are obtained depending on bedding orientation, and the results provide an explanation for the results obtained in the tests. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
12.
Z.T. Karpyn A. Alajmi F. Radaelli P.M. Halleck A.S. Grader 《Engineering Geology》2009,103(3-4):139-145
Multi-phase flow in fractured rocks plays an important role in any hydrocarbon recovery process, be it for environmental remediation or natural oil and gas extraction. Fractures may form the primary production conduits, and the mass transport at the fracture interfaces with the matrix determines the effectiveness of extraction processes. This paper presents specific evidence for a relationship between fracture apertures and the porosity of the adjoining perpendicular layers in Berea sandstone samples. Measurements of fracture apertures were done with high-resolution Micro-Computed Tomography (MCT) with a voxel resolution of about 0.05 mm in three dimensions. Multi-phase fluid flow experiments were done using a medical CT scanner with a voxel resolution of about 1.00 × 0.25 × 0.25 mm. MCT evidence shows a correlation between aperture and the porosity of the intersected layers. The comparison was made by generating two-dimensional maps of matrix porosity and CT values adjacent to the fracture and of the corresponding fracture apertures. High-porosity layers are lined up with large fracture apertures. Multi-phase fluid experiments provided hydraulic evidence that the high-porosity layers have high permeability. Oil injection into a water-saturated sample was tracked by a sequence of transverse scans near the downstream tip of a fracture. The hydraulic evidence from the two-phase flow experiments also confirms high permeability in fracture strips adjacent to high-porosity and high-permeability layers. The reasons for the relationship between fracture aperture and the properties of the adjacent layers are not fully understood. Some explanation for the physical and hydraulic observations rests in the method of fracturing, fracture propagation, and the lithological characteristics of the rock. 相似文献
13.
B.D.G. Smart J.M. Somerville B.R. Crawford 《Geotechnical and Geological Engineering》1999,17(3-4):157-176
Conventional so-called triaxial test cells apply the axial stress to a cylindrical sample using steel platens, with the confining stress developed via an annulus of hydraulic fluid retained by a liner in a pressure cell. This does not allow differentiation between the two principal stresses around the core and inhibits the realism with which the rocks can be tested, for example in determining the effect of the intermediate principal stress on the strength of the sample.This paper describes the development and application of a new test cell – believed to be the first in the world – which enables truly triaxial stresses to be applied to cylindrical core samples, opening up the possibility to test rocks routinely in a more realistic manner. An array of 24 trapped tubes replace the single annulus which usually generates the uniform radial stress. Selective pressurization of the tubes enables differential radial stresses to be generated, while axial stresses are applied as before through steel platens. The first results of multi-state failure and permeability stress sensitivity of samples tested in the cell are presented. These demonstrate the influence of the intermediate principal stress on measured rock properties and the orientation of induced fracture planes. 相似文献
14.
Qingquan Liu Yuanping Cheng Kan Jin Qingyi Tu Wei Zhao Rong Zhang 《Environmental Earth Sciences》2017,76(4):173
Underground borehole drilling usually causes instability in the surrounding coal due to in situ stress redistribution (including stress concentration and stress release). However, the mechanisms of unloading-induced coal strength reduction are still poorly understood. The primary objective of this study is to investigate the effect of confining pressure unloading on soft coal strength reduction for borehole stability analysis. A series of mechanical tests were conducted on both the traditionally and newly reconstituted coal samples under two different experimental stress paths, including conventional uniaxial/triaxial compression and triaxial compression with confining pressure unloading. The unloading stress path was obtained by analyzing the stress redistribution around a borehole, to capture a more accurate coal mechanical response. According to our experimental results, plastic deformation generated before failure under the unloading stress path is smaller than that generated under the conventional loading stress path. Furthermore, the cohesion of the traditionally and newly reconstituted samples diminishes approximately by 44.77 and 29.66%, respectively, with confining pressure unloading, indicating that there is a significant reduction in coal strength due to confining pressure unloading. The mechanism for unloading-induced coal strength reduction comes from confining pressure unloading-induced increase in shear stress on the fracture surface and a decrease in shear strength. This effect increases the shear slipping potential, whose driving force generates tension fractures at both ends of the preexisting fractures. 相似文献
15.
为了揭示应力扰动和卸载围压作用下大理岩损伤破裂的物理过程和非线性力学行为,采用GCTS RTR-2000伺服加载岩石力学试验机进行了岩石疲劳卸围压试验,同时对破坏试样进行了压后裂纹形态CT扫描可视化分析。结果表明：周期性的加卸载作用对大理岩起到了主因损伤作用,卸围压的作用对大理岩起到了根本性的破坏作用。岩石疲劳循环形成滞回环,滞回环面积由疏变密,滞回环加载和卸载曲线接近重合,加卸载模量近似相等;岩石经过卸围压作用,岩石的轴向、径向和体积应变表现为不同程度增大,表明应变对围压降低具有强敏感性,敏感程度由高到低依次为体积应变、径向应变和轴向应变;由于疲劳循环的影响,卸围压作用产生的围压降幅随循环次数增多而降低,卸围压时长随循环次数增多而减少;量化宏观应变变形,求得应变损伤指数 、 、 ,疲劳循环次数越多,应变损伤指数越大;岩石破坏后细观CT扫描揭示了疲劳循环损伤对岩石破裂形态影响的内在机制。随疲劳循环次数的增加,裂纹密度和规模显著增加。研究成果可为地下工程疲劳活动规律和开挖卸荷问题提供理论和模型支撑。 相似文献
16.
We report experimental measurements of bulk permeability changes due to a shear zone that is induced in siliceous mudstones collected from the Koetoi and Wakkanai Formations, northern Hokkaido, which are known to show different relationships between fault/fracture distribution and groundwater flow. We evaluate distributions of volumetric deformation in the induced shear zones by using micro-focus X-ray computed tomography. Measured permeability evolution while achieving the peak axial stress for specimens differed for the samples of the two formations. Permeability did not change obviously during shear for the Koetoi Fm. specimens, but in the Wakkanai Fm. specimens, the bulk permeability increased by a factor of 2.5 after reaching the peak stress. The difference in permeability change in these experiments can explain the differences in relationships between in situ groundwater flow and fracture distribution for the two formations. Analyses of the X-ray images reveal that this difference should reflect the differences of the volumetric deformation in the induced shear zones. Pore collapse occurred in the shear zone in the Koetoi Fm. specimen, which leads to porosity reduction, whereas fracture damages developed in the Wakkanai Fm. specimen, increasing porosity. These differences in the microstructure may reflect differences in yielding criteria for these host rocks. 相似文献
17.
高温作用后花岗岩三轴压缩试验研究 总被引：2，自引：0，他引：2
为综合考察温度、围压对花岗岩力学性质及破坏方式的影响,在高温（25℃～1 000 ℃）作用后,利用MTS815.02电液伺服材料试验系统对花岗岩岩样进行不同围压作用下的三轴压缩试验。研究结果表明,（1）围压一定时,经历不同高温作用后花岗岩三轴压缩全应力-应变曲线经历了压密、弹性、屈服、破坏、塑性流动5个阶段;（2）经历不同高温作用后岩样三轴抗压强度与围压呈非线性二次多项式增长关系,围压为40 MPa时的抗压强度比单轴抗压强度提高了382.30%;常规三轴压缩条件下,400 ℃是花岗岩力学参数的阀值温度;（3）经历高温作用后,岩样弹性模量随围压升高呈增大趋势,围压为40 MPa时的弹性模量比单轴时提高了90.26%;随温度升高呈二次非线性减小,1 000 ℃时的弹性模量比25℃时降低了57.16%;（4）花岗岩的失稳型式同时取决于围压和温度。单轴压缩状态下,随着温度的升高,岩样变形破坏型式由脆性破裂向塑性变形过渡,失稳型式在低温时为突发失稳、中高温为准突发失稳,温度高于800 ℃为渐进破坏;三轴压缩状态下,随着围压的增大,岩样破裂型式由脆性张拉破裂逐渐向剪切破裂过渡,岩样的失稳型式以突发失稳为主。在试验温压范围内,影响花岗岩力学性质的首要因素是温度,其次是围压。 相似文献
18.
Results are presented for three-dimensional planar fracture propagation in the presence of variations in confining stress, reservoir properties and frac-fluid viscosity when the well-bore pressure is constant throughout the frac-job. Solid rock deformation during the frac-job is described by the dislocation method with singular integral equations, and the fluid flow in the fracture is represented by the finite element method. A convergence study is undertaken on the three-dimensional numerical model, and good agreement is obtained with results from laboratory tests and from the simpler circular model. 相似文献
19.
Hema Siriwardane Igor Haljasmaa Robert McLendon Gino Irdi Yee Soong Grant Bromhal 《International Journal of Coal Geology》2009,77(1-2):109-118
The permeability of coal samples from Pittsburgh Seam was determined using carbon dioxide as the flowing fluid. The confining pressure was varied to cover a wide range of depths. The permeability was determined as a function of exposure time of carbon dioxide while the confining stress was kept constant. The porosities of the coal samples were found to be very low and most of the samples had porosities less than 1%. The permeability of these coal samples was very low—less than 1 μD. Since the objective of this study was to investigate the influence of CO2 exposure on coal permeability, it was necessary to increase the initial permeability of the coal samples by introducing a fracture. A longitudinal fracture was induced mechanically, and CT scans were taken to ensure that the fracture was present throughout the sample and that the sample was not damaged otherwise during the process. In this study, the permeability of coal was determined by using pressure transient methods. Two types of pressure pulses were used: A-spike and Sine-6 pressure transients. It was first established that the permeability of fractured coal samples did not change with exposure time when an inert gas (Argon) was used as the fluid medium in the experiments. However, the permeability of coal samples decreased significantly when carbon dioxide was used as the fluid medium. This reduction can be attributed to the coal swelling phenomenon. The results show that the permeability reduction in fractured coal samples can be over 90% of the original value, and the exposure time for such reductions can range from 1.5 days up to a week, typically about 2 days under laboratory conditions. The permeability decreased significantly with the increase in confining pressure. The higher confining pressure appears to close internal fractures causing a reduction in permeability. 相似文献
20.
Micro- and macro-behaviour of fluid flow through rock fractures: an experimental study 总被引：2，自引：1，他引：1
Microscopic and macroscopic behaviour of fluid flow through rough-walled rock fractures was experimentally investigated. Advanced microfluidic technology was introduced to examine the microscopic viscous and inertial effects of water flow through rock fractures in the vicinity of voids under different flow velocities, while the macroscopic behaviour of fracture flow was investigated by carrying out triaxial flow tests through fractured sandstone under confining stresses ranging from 0.5 to 3.0 MPa. The flow tests show that the microscopic inertial forces increase with the flow velocity with significant effects on the local flow pattern near the voids. With the increase in flow velocity, the deviation of the flow trajectories is reduced but small eddies appear inside the cavities. The results of the macroscopic flow tests show that the linear Darcy flow occurs for mated rock fractures due to small aperture, while a nonlinear deviation of the flow occurs at relatively high Reynolds numbers in non-mated rock fracture (Re?>?32). The microscopic experiments suggest that the pressure loss consumed by the eddies inside cavities could contribute to the nonlinear fluid flow behaviour through rock joints. It is found that such nonlinear flow behaviour is best matched with the quadratic-termed Forchheimer equation. 相似文献