Numerical Modeling of Natural Fracture Distributions in Shale

The production efficiency of shale gas is affected by the interaction between hydraulic and natural fractures. This study presents a simulation of natural fractures in shale reservoirs, based on a discrete fracture network (DFN) method for hydraulic fracturing engineering. Fracture properties of the model are calculated from core fracture data, according to statistical mathematical analysis. The calculation results make full use of the quantitative information of core fracture orientation, density, opening and length, which constitute the direct and extensive data of mining engineering. The reliability and applicability of the model are analyzed with regard to model size and density, a calculation method for dominant size and density being proposed. Then, finite element analysis is applied to a hydraulic fracturing numerical simulation of a shale fractured reservoir in southeastern Chongqing. The hydraulic pressure distribution, fracture propagation, acoustic emission information and in situ stress changes during fracturing are analyzed. The results show the application of fracture statistics in fracture modeling and the influence of fracture distribution on hydraulic fracturing engineering. The present analysis may provide a reference for shale gas exploitation.     

Evaluation of stress strain non-uniformities in the laboratory direct simple shear test specimens using 3D discrete element analysis

The direct simple shear (DSS) device is one of the commonly used laboratory element testing tools to characterize the shear behaviour of soil. The interpretation of results from an element test requires understanding of the degree of stress and strain non-uniformities in a given test specimen. So far, studies on stress and strain non-uniformities in the DSS test have been conducted using direct boundary measurements of stresses in laboratory specimens supported by a continuum based analytical approach. Discrete element modelling now provides a means of modelling the soil behaviour in a realistic manner using a particulate approach. Accordingly, the performance of a DSS specimen was modelled using discrete element modelling with emphasis on assessing stress and strain non-uniformities in the specimen during shearing. The approach allowed for the numerical determination of stresses not only at the boundaries, but also within the DSS specimen. It was shown that mobilised stress ratio distribution throughout the shearing phase for the majority of specimen volume at locations near the central planes parallel and perpendicular to the direction of shearing is fairly uniform. Finally, it was noted that the potential for particle slippage at locations near the specimen centre can result in non-uniform shear strain distributions.     

利用球体剖分瓦块构建真三维数字地球平台

全球离散网格是面向空间大数据的模型框架,常用于构建数字地球平台。基于球体的剖分瓦块不仅可以构建真三维的数字地球模型,而且可以实现天地一体化的空间数据集成、融合、表达和应用。本文详细论述了球体大圆弧QTM八叉树网格的剖分原理、网格几何特征分析和编解码方法等理论体系,并利用剖分瓦块实现了球体的任意分割以及地下、地表和空中实体的可视化建模。研究表明,球体QTM网格具有剖分规则简单、体系规整、几何特征明晰,适用性强等特点,尤其是可以推广到椭球。因而,该方案可用于天地一体化的空间数据的组织、管理与应用。     

矢量河网渐进式传输的多尺度表达模型

矢量河网数据渐进式传输是制图综合的逆过程,从几何特征出发化简曲线的方法忽略了曲线的形态特征。鉴于此,以曲线轴线为基准,基于曲线弯曲层次化提取河流曲线数据,并将提取的曲线数据分层组织,构建结合目标层和几何细节层的河网多尺度表达模型。基于该模型开发了矢量河网数据的渐进式传输系统,验证了该方法的有效性。     

多尺度表达中线状要素的综合不确定性评价模型

在考虑节点化简的基础上建立了节点数据不确定性评价模型,基于曲线光滑模型建立了线元模型不确定性评价模型,在此基础上,根据不确定性传播律构建了由数据不确定性和模型不确定性合成的线状要素多尺度表达不确定性的综合评价模型。实验表明,综合不确定性指标值作为线状要素多尺度表达不确定性的量化指标是有效的。可将其用于计算线元不确定带的宽度,解决线状要素多尺度表达不确定性空间分析和推理问题;并用于线状要素多尺度表达的质量评价与控制。     

基于DEM-CFD耦合的气吸式排种器仿真研究

为提高大白菜等小粒径精密播种机的机械化水平,设计了一种小粒径气吸式排种器.首先利用JPS-12排种器性能检测试验台对排种器进行测试,得到不同参数组合下的性能指标与最优参数组合.然后使用计算流体力学方法（CFD）,借助FLUENT软件分析了吸种器内部流场的分布,得到了吸种器内部压力分布云图和吸种孔截面云图.最后基于离散元法（DEM）建立大白菜种子颗粒模型,对排种器仿真模型进行简化和网格划分,完成了小粒径气吸式排种器DEM-CFD耦合仿真实验.对比台架与仿真试验结果,得出如下的结论：当排种盘转速为20 r/min,真空度为2.2 kPa时,排种性能最佳.     

基于地震信号波形形态差异的面波噪声稀疏优化分离方法

实际地震信号通常可表示为具有波形特征差异的多种基本波形信号的线性组合,如叠前道集中的工频干扰噪声与有效波信号、面波噪声与体波信号等.选择单一数学变换方法,往往不易实现地震信号的稀疏表示.近年来发展的形态成分分析理论,通过联合多种数学变换,可实现对复杂信号的稀疏表示.本文根据单道地震记录中面波与体波信号波形结构特征的差异性,提出一种基于形态成分分析的面波噪声衰减方法.针对面波的低频、窄带以及频散特性选择一维平稳小波变换作为其稀疏表示字典,而针对体波波形的局部相关特性选择局部离散余弦变换作为其稀疏表示字典,建立基于双波形字典的形态成分分析模型,通过求解该稀疏优化问题获得最终的信噪分离结果.理论模型和实际地震资料处理证实该方法不仅能够衰减单炮地震记录中的强面波干扰噪声,同时能够更好地保护有效信号的波形特征与频谱带宽,为地震资料的后续处理和分析提供良好的数据基础.     

开挖条件下含陡倾结构面顺层岩质边坡破坏模式与稳定性预测

顺层岩质边坡易发生失稳破坏,当边坡中发育有顺坡向陡倾结构面时,更不利于边坡稳定。以贵州某水电站大坝左岸含陡倾结构面顺层边坡为例,在综合分析地质条件及开挖扰动的基础上,结合离散元软件UDEC,分析了边坡的变形破坏模式和稳定性。研究结果表明,边坡可能发生的变形破坏模式主要有滑移、拉裂—滑移两种;自然状况下及开挖后,边坡都有沿断层f9、卸荷裂隙L1及岩层面发生滑移的趋势,且工程开挖导致边坡沿该结构面发生内部滑动;对边坡采用预应力锚索加固后,变形得到有效控制,位移数值计算值与实际监测值基本吻合。     

巴东组典型红层软岩单轴压缩试验细观组构特征

红色粉砂质泥岩和泥质粉砂岩是巴东组特殊性岩土的代表,具有遇水易崩解特性。根据岩样单轴压缩试验,基于PFC_2D程序,建立中硬岩、软岩单轴压缩试验数值模型;模型选用平行黏结颗粒接触模型。根据应力-应变曲线特征,采用分段定量参数标定法对软岩试样的细观参数进行标定;且通过调整法向和切向黏结强度比值2D program. With the characteristics of stress-strain curve, subsection quantitative parameter calibration method was used to calibrate the microscopic parameters of soft rock samples. The adjustment method and the ratio of tangential bond strength(σ_c/τ_c) control specimen under uniaxial compression failure mode. The uniaxial compression test of silty mudstone and argillaceous siltstone with different weathering degree under saturated and natural state was simulated. The distribution and evolution of meso-fabric parameters such as normal contact force, tangential contact force, coordination number and porosity were analyzed. The results show that the numerical method can well simulate the uniaxial compression test process of medium hard rock and soft rock. Except for medium weathered silty mudstone, weathering degree and water immersion condition can only affect the size of the contact force of sample particles in the statistical angle range, but cannot affect the distribution form. At the same time, weathering degree and water immersion condition prolonged the loading time of significantly decreased coordination number, which decreased with the increase of the number of cracks. Flooding condition and weathering degree have great influence on the porosity evolution of argillaceous siltstone. The degree of weathering has a great influence on the porosity evolution of silty mudstone, but the condition of flooding has little influence.      

均匀弹性分层介质模型中的同震位移、应变以及应力

地震发生时产生的同震位移、应变以及应力变化,特别是同震应力的变化,在地震触发等问题的研究中有着重要的意义.本文进一步发展了基于均匀弹性水平层状介质,利用广义反射透射系数矩阵和离散波数计算同震位移的方法,使之可以计算相应的应变、应力以及同震库仑应力变化.可适用于多种情况,接收点可以位于地表以及地表以下,震源类型可以是剪切位错源以及拉张位错源.通过与半无限介质的解析解相比较,结果一致,验证了方法的可靠性以及计算精度,可以用于计算地震之后库仑应力变化,为判断余震分布提供参考.在计算同震位移时,使用了梯形积分与Filon积分相结合的积分方式,即提高了同震位移计算的速度,又保证了计算精度,有利于反演问题研究.