可变形孔隙介质中热、水耦合力学问题的代数多格子分析方法

研究了孔隙介质中包括热和质量传递的全耦合多相流问题的代数多格子分析方法· 数学模型包括质量、线性矩、能量平衡方程和本构方程 ,以位移、毛细压力、汽压和温度为基本变量 ,模型中采用了考虑毛细压力关系的修正有效应力概念 ,并考虑相变、热传导、对流和潜热交换 (汽化_冷凝 ) ,气相是由易混合的干空气和水蒸气组成 。

页岩“刚-弹嵌合”孔隙骨架模型及超压状态孔隙度测量方法——以四川盆地南部志留系龙马溪组深层超压硅质页岩为例

基于页岩孔隙特点、孔隙骨架组成并结合超压状态下孔隙、骨架应力分析,建立页岩储集层“刚-弹嵌合”孔隙骨架模型,解析弹塑性骨架超压变形引起孔隙度增大的孔隙变形机制,提出1种“动态”变形孔隙度测量方法,并对四川盆地南部(简称川南)志留系龙马溪组超压状态真实地层条件孔隙度进行测算。结果表明:(1)页岩储集层是无机岩石颗粒与有机质的混合体,构成了刚性骨架支撑的无机质孔隙和弹塑性骨架支撑的有机质孔隙“刚-弹嵌合”特殊孔隙结构,有机质孔、无机质孔混杂共生。(2)在地层超压作用下,无机质孔隙变化相对很小以至可以假设其孔隙度保持不变,而有机质孔隙由于骨架压缩可发生较大形变,导致孔隙半径增大,连通性增强,孔隙度增加。(3)通过高注入压力氦气法孔隙度测量及超高压煤油法变孔隙压力孔隙度测量相结合,建立的“动态”变形孔隙度测量方法既能测量到常压条件不连通的微孔孔隙度,又能测量到有机质骨架压缩变形导致的孔隙度增量。(4)页岩孔隙变形机制会产生地层条件孔隙度高于常压孔隙度的“反常”现象,超压页岩并非真正的“超低孔”储集层,孔隙度甚至可以大于10%。通过川南地区L210井实例测量,验证了该方法的实用性和可靠性。

颗粒材料内部滑动变形局部化的离散元模拟

颗粒材料在加载过程中表现出非常复杂的变形性质。在微观尺度上,单个颗粒的运动、单个孔隙胞元内的变形都是非均匀的,但也不是完全随机、没有规律可循的,而是呈现一定结构性的分布,如微带、剪切带等。本文用基于孔隙胞元的离散元方法对颗粒体进行双轴加载数值试验,模拟了以滑动变形表征的变形局部化现象。数值结果发现,对应加载过程中的不同阶段,滑动变形存在几种不同的变形局部化形式。同时,在加载过程中颗粒体内部一直都存在与平均滑动变形方向相反的负滑动现象,这说明在速度梯度场不连续的区域同时存在弹性卸载和塑性流动。

弹性多孔介质粘土膨胀和微粒运移的数学模拟方法

孔隙介质的变形、粘土的膨胀、孔隙介质内部微粒的释放、运移和滞留及注入流体携带的外部微粒的入侵是导致孔隙介质的孔隙度和渗透率发生改变的主要因素。在注水开发油田过程中由于孔隙变形、粘土的膨胀、孔隙介质内部微粒的释放、运移、滞留和微粒入侵导致的油层伤害是一个普遍现象。在论述孔隙变形、粘土的膨胀、孔隙介质中微粒的释放、运移和滞留及微粒在孔隙介质表面吸附和在孔喉堵塞导致油层伤害机理的基础上 ,建立了一个综合的描述油层伤害数学模型并采用有限差分法进行了数值求解。利用数值运算的结果研究了由油层内部微粒。

纯钼粉末-包套等径角挤压的多尺度研究

采用离散元分析软件PFC-2D对纯钼粉末材料的单道次等径角挤压过程从细观角度进行数值模拟,获得其变形过程中载荷、颗粒和孔隙的变化规律。模拟结果表明,等径角挤压对粉末材料具有强烈的致密化作用,且整个变形过程可以分为4个阶段:颗粒重排、初始变形、过渡变形和稳定变形。分析认为,冲头压力首先使颗粒重排减少大孔隙,之后,由于压力增大使小孔隙闭合,剪切作用使颗粒和孔隙发生变形,结合强大的静水压力使材料致密。在400℃条件下的纯钼粉末黄铜包套单道次挤压实验结果与模拟结果具有较好的一致性,验证了所建离散元模型的可靠性。

降温过程中孔隙的结晶变形

盐风化过程中盐结晶在孔壁产生的结晶压力是导致多孔介质材料变形与破坏的主要原因。基于结晶动力学理论,考虑了晶体与孔壁的相互作用,建立了降温过程中孔隙晶体生长模型,对降温过程中不同含盐量、含水量和荷载条件下的孔隙盐胀变形行为进行了模拟和试验分析。结果表明,孔隙的结晶变形受盐结晶体积、起始孔隙直径和盐结晶形状(盐结晶长宽比)的影响,在相同降温条件下,水盐含量影响了降温过程中盐结晶体积,而荷载的增大迫使盐结晶产生更多的横向生长(长宽比增大)。本模型为揭示降温结晶过程中多孔介质盐胀变形机制和计算盐胀变形提供了新的途径。

不同水压加载下煤体裂隙渗流数值模拟

为研究煤体在不同水压加载下内部裂隙的渗流运动和孔隙变形规律,应用纽迈核磁共振(nuclear magnetic resonance,NMR)扫描与图像重构技术建立煤岩微孔隙渗流模型,而后借助COMSOL软件,在煤体两侧为固定边界,其上部边界分别进行1~10 MPa水压逐级加载的条件下,对煤体的微观裂隙通道进行渗流运动的数值模拟分析。模拟结果表明:煤体中只有贯通裂隙参与渗流运动,非贯通孔裂隙不参与渗流运动;渗流过程最大流速先是呈现较大速率的正比例增长,在水压达到4 MPa时会突然保持稳定,在水压超过5 MPa后又呈现出较小速率的正比例增长。裂隙介质最大变形会在水压接近4 MPa时到达一个峰值然后突然反弹减小,又逐渐缓慢增大直至最后趋于稳定。应力云图特征表明,渗流过程中应力场变化趋势与裂隙位移变形趋势一致,渗流过程中的水力耦合作用是水压在4 MPa时渗流规律发生改变的主要原因。

海陆过渡相致密砂岩储层Biot系数自适应预测方法研究

沁水盆地石炭—二叠系海陆过渡相致密砂岩气测异常极为普遍,具有致密气勘探、开发潜力,但目前该地层致密砂岩缺少Biot系数的相关研究。Biot系数(α)的准确预测对地震反演、压裂设计、出砂趋势预测、储层应力敏感性、井眼轨迹优化及井壁稳定性分析等方面均具有重要参考价值。为了弥补该不足,以海陆过渡相致密砂岩储层为研究对象,结合Gassman-Biot-Geertsma方程,提出基于自适应方法的Biot系数预测方法。研究结果表明,利用自适应方法能有效提取目的层致密砂岩的基质矿物体积模量(Ko)和干岩石体积模量(Kd)。Ko与Kd均与纵波速度(vP)具有较好的正相关性。该致密砂岩的孔隙度φ平均值为4.11%,α平均值为0.179。α较低的原因与致密砂岩所经历的强压实及胶结作用相关。将提出的Biot系数预测新方法分别与孔隙度方法、声学参数方法及考虑孔隙空间变形3种方法进行了对比,结果表明,利用孔隙度和声学参数方法计算所获得的α与本文结果具有较好的对应关系,验证了本文方法的有效性。

凝析油气体系流固耦合相平衡计算新方法

在分析了孔隙介质内表面吸附、毛细凝聚、毛细管压力等界面物理化学效应和应力变形对孔隙介质中流体相态影响的现象学特征和影响机制的基础上,通过在大尺度空间常规流体相平衡热力学模型中引入界面物理化学效应的影响,同时通过高才尼-卡尔曼方程将毛细管半径与孔隙介质储渗特性的应力敏感性研究成果相关联,建立了同时考虑储层应力变形和界面物理化学效应影响的微孔隙尺度条件下的低渗特低渗凝析气藏多相流体流固耦合露点压力、p-T相图及定容衰竭相平衡热力学计算模型。该模型的初步应用表明,其相态模拟计算结果能更为合理地解释孔隙介质环境中的凝析油气体系相态特征实验研究结果。

基于ALE方法的油水两相流固耦合模型研究

文章应用任意拉格朗日-欧拉方法(ALE)对油水两相流固耦合问题进行了研究;详细推导了ALE描述下的两相渗流与变形多孔介质的耦合数学模型方程,解决了孔隙骨架变形介质与渗流方程的统一描述问题;通过编制相应的ALE有限元程序,分析了注水驱替过程,检验了所提出的模型及相关数值算法。对该模型方程讨论发现,若取ALE网格移动速度为岩层骨架变形速度将简化两相渗流方程,降低数值求解难度。

一种全耦合多相流分析的并行计算方法

研究了孔隙介质中热、水和汽流全耦合分析的并行计算方法．模型中采用了考虑毛细压力关系的修正有效应力概念，并考虑了相变和潜热传递．基本变量为位移、毛细压力、汽压和温度．并行程序是在国家高性能计算中心（北京）的曙光１０００Ａ上借助ＰＶＭ（ＰａｒａｌｅｌＶｉｒｔｕａｌＭａｃｈｉｎｅ）软件系统实现的。

Environmental effects induced by excavation

Based on 3D Biot’s consolidation theory and nonlinear Duncan-Chang’s model, a 3D FEM (finite element method) program is developed considering the coupling of groundwater seepage and soil skeleton deformation during excavation. The comparison between the analysis result considering the variation of water head difference and that without considering it shows that the porewater pressure distribution of the former is distinctly different from that of the latter and that the foundation pit de- formations of the former are larger than those of the latter, so that the result without considering the variation of water head dif- ference is unreliable. The distribution rules of soil horizontal and vertical displacements around the pit and excess porewater pressure are analyzed in detail in time and space, which is very significant for guiding underground engineering construction and ensuring environment safety around the pit.

Influences of rainfall infiltration on stability of accumulation slope by in-situ monitoring test

In order to improve the understanding of the fundamental mechanism of rainfall infiltration induced landslides in accumulation slope and to clarify some important characteristics of slope performance,artificial rainfall simulation tests and field synthetic monitoring were carried out on a typical accumulation slope of Shangrui Freeway in Guizhou Province,China.The monitoring results show that the most accumulation landslides caused by rainfall infiltration are shallow relaxation failure,whose deformation zone lies within the top 0-4 m soil layer.The deformation of slope gradually reduces from the surface,where the greatest deformation lies in,to the deep part of slope.The average percentage of infiltration during the first 2 h is 86%,and then it reduces gradually with time because of the increase of the surface runoff.The average percentage of infiltration drop to a relatively stable value(50%)after 6 h.Rainfall infiltration causes obvious increase of pore-water pressure,which may result in a reduction of shear strength due to a decrease in effective stress and wetting-induced softening.The double-effect of rainfall infiltration is the main reason of rainfall infiltration induced landslides in accumulation slope.

Three-dimensional consolidation deformation analysis of porous layered soft soils considering asymmetric effects

Long-term settlements for underground structures, such as tunnels and pipelines, are generally observed after the completion of construction in soft clay. The soil consolidation characteristic has great influences on the long-term deformation for underground structures. A three-dimensional consolidation analysis method under the asymmetric loads is developed for porous layered soil based on Biot's classical theory. Time-displacement effects can be fully considered in this work and the analytical solutions are obtained by the state space approach in the Cartesian coordinate. The Laplace and double Fourier integral transform are applied to the state variables in order to reduce the partial differential equations into algebraic differential equations and easily obtain the state space solution. Starting from the governing equations of saturated porous soil, the basic relationship of state space variables is established between the ground surface and the arbitrary depth in the integral transform domain. Based on the continuity conditions and boundary conditions of the multi-layered pore soil model, the multi-layered pore half-space solutions are obtained by means of the transfer matrix method and the inverse integral transforms. The accuracy of proposed method is demonstrated with existing classical solutions. The results indicate that the porous homogenous soils as well as the porous non-homogenous layered soils can be considered in this proposed method. When the consolidation time factor is 0.01, the value of immediate consolidation settlement coefficient calculated by the weighted homogenous solution is 27.4% bigger than the one calculated by the non-homogeneity solution. When the consolidation time factor is 0.05, the value of excess pore water pressure for the weighted homogenous solution is 27.2% bigger than the one for the non-homogeneity solution. It is shown that the material non-homogeneity has a great influence on the long-term settlements and the dissipation process of excess pore water pressure.

Prediction method of reservoir pore types based on pore shape substitution

Carbonate,tight sandstone,and shale reservoirs have many pore types,and the relationship between the porosity and elastic parameters is extremely discrete due to the complex pore shape.This paper presents a method for predicting reservoir pore types based on pore shape substitution.The pore shape substitution allows for accurately characterizing the changes in the elastic properties of the rock with the changes in pore shape,assuming there are no changes in terms of minerals,porosity,or fl uids.By employing a multiple-porosity variable critical porosity model,the eff ective pore aspect ratio could be inverted from the velocities of the rock.To perform pore shape substitution,we could replace the eff ective pore aspect ratio with another pore aspect ratio or increase/decrease the volume content of diff erent pore shapes.The reservoir pore types could be evaluated by comparing the differences in the reservoir velocities before and after the substitution of the pore shape.The test results pertaining to the theoretical model and the well logging data indicated that the pore shape substitution method could be applied to characterize pore types in terms of separating the eff ects of the pore shapes from the eff ects of the minerals,porosity,or fl uids on the velocities.

The Creeping Shores of the Golden Horn

In a soft clay layer overlain by a thick man made ground layer, as in the case of the Unkapam shores of the Golden Horn, excess pore pressures have remained for long periods and the soft clay layer has hardly undergone few volumetric deformations. Along the shores of the Golden Horn such creep of the soil towards the sea has been detected at more than 40 mm in the last 26 months. The measurements of those movements are examined in this paper. Our research points out that the local failure of a soil element or of a particular layer differs from the general failure of the soil mass. Furthermore, the large masses of unfailed soil which overlie the soft layer along the shores of the Golden Horn delay the general failure of the slopes. We conclude that the shear strains producing excessive pore pressures is the cause of the creep observed. Because a proper solution still need to be found for a sustainable stability of the area, it is necessary to continue with the measurements of the Golden Horn＇s creeping shores.

Deformation of ductile cuttings from sandstone in compaction process and experimental study of influence on porosity

Deformation of ductile cuttings from sandstone in the mechanical compaction process was designed through the "experimental system of triaxial rock deformation",and the influence on porosity was studied by looking into the deformation characteristics of ductile cuttings. The design indexes are as follows: simulated depth 0- 4 000 m,interval depth 500 m,and pressure range 0- 120 MPa at interval of 1. 5 MPa. The experimental results show that the porosity decreases as buried depth increases,indicating a negative relationship between them. The amount of compression was mainly obtained by porosity reduction and cutting deformation. Deformation of ductile cuttings is mainly ductile deformation; and deformation of crystal fragments is mainly expressed as brittle fracture,resulting in decrease of particle size. The research is of certain value for the exploration and development of oil and gas.

Modeling of void closure in diffusion bonding process based on dynamic conditions

The dynamic conditions for plastic deformation mechanism,surface source mechanism,interface source mechanism and creep mechanism in the diffusion bonding process are proposed.Based on these dynamic conditions,a model for void closure in the diffusion bonding process is derived.The effects of diffusion bonding parameters on the bonding mechanisms are analyzed.For the diffusion bonding process of TC4 alloy,at a low diffusion bonding temperature or pressure,or for a short time,the interface source mechanism plays a main role.But,the creep mechanism is the dominant mechanism and operates until the diffusion bonding is fulfilled.As the diffusion bonding time increases,the surface source and interface source mechanism enhance and then stop at a certain stage of diffusion bonding,while the creep mechanism enhances continuously.As the diffusion bonding temperature or pressure increases,the interface source mechanism weakens and the other mechanisms enhance.The maximum and average errors between the calculated and the experimental results in the diffusion bonding for TC4 alloy are 12.86% and 5.79%,respectively.