岩体中节理裂隙面开度的测量方法

本文给出了单裂隙岩体的裂隙面平均开度和等效开度的实用测量方法 ,并推导出了相应的计算公式     

三维裂隙网络渗流数值模型研究

本文根据岩体裂隙空间结构特征和渗透机制，将复杂裂隙系统划分为三大类型：带状断层类、面状裂缝类和管状孔洞类，确定相应的裂隙计算单元（体单元、面单元和线单元）和渗流方程，然后按各种裂隙单元的空间组构关系，建立了由多种裂隙单元构成的裂隙网络三维渗流数值模型，在模型中采用双面单元法描述断层面的阻隔水作用，有用管状线单元描述裂隙中的管道流和岩体中的排水孔。这种模型能充分表现出岩体中各类裂隙的几何形状和它们的     

非均匀荷载作用下层状岩体矩形裂隙力学特性分析

该文采用已发展的层状材料基本解对偶边界元方法,分析了层状裂隙岩体的力学特性。在分析无限域层状岩体中裂隙时,该对偶边界元方法退化为间断位移法。在建议的间断位移法中,只需沿裂隙一个面离散,采用9结点等参单元和非连续单元离散裂隙面。采用建议方法计算了作用有非均匀荷载矩形裂隙的间断位移。利用裂隙尖端附近的间断位移值,计算了应力强度因子。给出不同岩性组合情形时矩形裂隙应力强度因子的分布规律。     

水电工程大坝基岩三维随机裂隙岩体灌浆数值模拟

针对目前裂隙岩体灌浆数值模拟主要以单一裂隙或者二维裂隙网络为研究对象,且多未考虑隙宽随机性分布的现状,该文首先利用Monte-Carlo方法构建隙宽服从随机分布且耦合灌浆孔的三维随机裂隙网络灌浆模型;然后采用三维离散元软件（3DEC）模拟多级水灰比浆液在裂隙网络中的扩散过程,并分析压力场、单宽流量场的分布特征。运用该方法模拟某水电站灌浆孔基岩帷幕灌浆过程,结果表明:压力由灌浆孔壁向裂隙内呈非线性衰减,在灌浆孔附近压力衰减速率最快;浆液流量因水灰比的逐级变浓而随着灌浆时间的增加呈阶梯状下降;将模拟灌浆量和灌浆时间与实际值对比,相对误差分别为-17.11%和3.11%,模拟结果与实际值基本吻合,验证了该方法的可用性。     

裂隙岩体爆破数值模拟研究

岩体中的裂隙直接影响到爆炸应力波在岩体中的传播,进而影响到爆破效果。针对宏观闭合裂隙岩体的特点,采用LS—DYNA与离散元软件3DEC相结合的方法,分别模拟了含1条裂隙、2条平行裂隙和2条相交裂隙岩体中爆炸应力波的传播特点。结果表明,台阶爆破中应力波的分布并不均匀,应力波主要朝自由面的方向传播;闭合型宏观裂隙阻碍爆炸应力波的传播,岩体中裂隙越多,最小主应力降低的越快,2条裂隙时,炮孔附近的拉应力降低了约30%。     

基于热流耦合精细算法的大体积混凝土水管冷却数值模拟

基于有限元热流耦合精细算法进行大体积混凝土施工期温度场仿真分析,真实反映水管附近的温度梯度和水管水温沿程的变化,采用基于粒子迁徙的粒群算法对Dittus-Boelter方程进行参数识别,使之适用于描述冷却水流的强制对流特性.在通用有限元软件ABAQUS 平台上,开发热流耦合用户子单元,以官地碾压混凝土重力坝某一浇筑块为例验证热流耦合算法和用户子单元的可靠性和合理性.计算结果表明:精细算法能真实反映混凝土浇筑块的温度场,同时基于精细算法得到的施工期应力略大于等效算法.     

三维瞬态方形管流的热流固耦合数值模拟

以主动冷却发动机壁板为模型,考虑受均匀热流载荷作用下方形管在流体冷却过程中的共轭传热问题,建立了防热涂层、固体管道和冷却液的三维耦合模型。利用数值离散方法进行了瞬态热流固耦合分析,得到了固体结构和流场的瞬态温度场、界面热流及结构应力分布规律。结果表明:在冷却液的作用下结构温度能达到稳定值,但油冷情况下稳态温度值高于水冷情况;在流固界面处温度沿流向逐渐上升,且壁面热流分布在界面上下表面处随时间变化情况不同,在结构边角处出现较大的应力集中。     

浅埋煤层开采突水溃砂两相流的耦合数值研究

为探究浅埋煤层开采上覆含水松散层水砂两相流动规律,采用基于离散元软件PFC3D和有限元软件GID的耦合数值方法,模拟了上覆岩层中预制理想单裂隙在不同开度和倾角条件下突水溃砂全过程,分析了裂隙通道所受接触力、水流速度、水砂间拖曳力随时步的变化规律。结果表明:裂隙开度和倾角会改变突水溃砂过程中水砂突涌类型,对覆岩所受接触力、水流速度及其稳定所需时间产生较大影响,水砂间拖曳力主要受裂隙倾角的影响。裂隙通道入口处即上覆岩层的顶层在突水溃砂初期所受接触力最大,处于最危险状态;水流速度稳定值和流动稳定所需时间分别与裂隙倾角和开度成线性相关;对比裂隙通道底面侧,倾向侧水砂间拖曳力较大,水砂突涌更加剧烈。     

深地能源工程热水力多场耦合效应高效模拟方法

深地能源工程多场耦合效应数值模拟面临的主要难题有深部岩体的非线性力学特性、复杂的赋存环境、以及围岩-结构尺寸相差悬殊的计算瓶颈。针对深地能源工程井筒结构独特的细长型几何特点，将井筒简化为一维线单元，考虑井筒内流体沿井筒轴向的渗流传热，而井筒内流体与周围岩体的换热过程则采用等效换热系数近似考虑，套管和砂浆层的影响包含在等效换热系数中，利用该方法实现了远场尺度深地能源工程热-水-力多场耦合效应的高效模拟。依托中国京津冀及周边地区典型水热型地热田群井系统开展案例研究，不仅证明了该文所提出的数值模拟方法可兼顾百平方千米尺度深地能源工程多场耦合效应模拟分析的精度与效率，还揭示了深部热储温度场、渗流场、变形场的长期演化特征。     

地应力对含裂隙岩体爆破影响分析研究

随着深部开采环境逐渐复杂,为实现安全高效的工程爆破施工,针对深部开采爆破作业所面临的高地应力和穿越破碎带的问题展开分析研究.运用有限元分析软件ANSYS-LS/DYNA中的隐式-显式耦合分析程序对双向等压、双向不等压下含裂隙岩体进行数值模拟,研究高地应力区对含裂隙、弱面等岩体进行爆破开挖这一特殊工况.研究结果表明:深部...     

Coupled thermo-mechanical algorithm for fractured rock mass by the composite element method

To assess the influence of thermal stress on fracture deformation, a composite element algorithm of thermo-mechanical coupling for fractured rock mass is developed based on the composite element method (CEM). This study aims to investigate coupled processes associated with the (i) effect of temperature on mechanical deformation and (ii) effect of fracture aperture on heat transfer. The composite element contains fracture segments exhibiting arbitrary shapes with variables that can be interpolated from their mapped nodal variables; the mapped variables can be determined using the governing equations derived from the variational principle or virtual work principle. The proposed coupling algorithm can simulate the discontinuity of fractures, with consideration of the heat transfer of rock blocks and fractures, together with heat exchange among fractures and the adjacent rock mass. A computational mesh is generated without restrictions by explicitly embedding the fractures into the mapped composite elements, substantially simplifying the pre-process work. Analytic solutions to the transient temperature problem are examined to verify the proposed CEM algorithm. Two three-dimensional numerical models are developed to perform thermo-mechanical coupling analyses. These analyses are used to prove the advantage of the mesh handler and the reliability of the proposed algorithm. During coupling with the CEM model, the computational mesh requires no modification regardless of changes in fracture aperture. Results indicate that an increase in temperature leads to rock expansion, causing fracture deformation, which affects the general temperature of the fractured rock mass.     

通州区地热资源优化开采模式动态研究

地热井的优化开采对地热资源的集约高效利用意义重大。根据北京市通州区地层特征和地热井布局建立了三维热储模型,对储层岩体中热、水进行多尺度耦合模拟,利用抽水试验、回灌试验监测数据进行了模型校正。利用校正后的模型,计算了不同采灌量下的热突破时间,预测了现有模式下热突破引起的地温场变化以及不同采量下抽水漏斗的演化趋势,得出通州区域内25眼地热井开采100年后温度场和水位场的动态云图。基于模拟数据,结合通州区现有采灌条件,提出了“一采一灌”、“一采两灌”、“两采三灌”的布井方案,同时进行了不同采灌量下的温度场、水位场的数值模拟,提出了优化的采灌布井模式,为地热资源长期开发利用提供理论支撑。     

Coupled poromechanics-damage mechanics modeling of fracturing during injection in brittle rocks

Subsurface injection of fluids in a stress-sensitive naturally fractured rock faces the problem of near-wellbore fracture evolution and associated changes in rock properties. Numerical modeling of the changes in permeability and poroelastic properties of the near-wellbore region is challenging due to the coupling between fracture dynamics and poromechanics across multiple length scales of fractures and the host rock. We present a numerical framework to model anisotropic and dynamic evolution in rock properties based on a coupled formulation of fluid flow, rock mechanics, and fracturing, where fracturing-induced damage is used to update the rock properties. A generalized fixed-stress method, which accounts for damage-induced anisotropy in flow and deformation processes, is developed to sequentially solve the equations of flow, mechanics, and fracture evolution. We demonstrate the usefulness of our framework in quantifying the effects of injection rate variability, initial fracture distribution, and in-situ stress state on the evolution in permeability, elastic stiffness, and the Biot parameters. Our framework does not require the computational mesh to conform to existing or future fractures, allows simultaneous growth of multiple randomly distributed fractures, and can be implemented relatively easily in existing coupled flow-geomechanics simulators to extend them to model fracturing at the reservoir scale.     

各向异性双重孔隙介质的应力与油水两相渗流耦合理论模型

针对天然裂缝性油藏的特性,建立了描述双重孔隙介质中油水两相流体流动特性的流固耦合理论模型。该模型不仅考虑了渗透率的各向异性,而且考虑了岩石固体骨架变形的各向异性。渗流方程是依据双重孔隙的概念建立起来的,而固体骨架变形控制方程则是根据Biot 的等温、线性孔隙弹性理论建立起来的。同时,给出了横向各向同性及结构各向异性、固体材料各向同性时的双重孔隙介质的应力与油水两相渗流耦合理论模型。对该模型进行了简化,并将其简化后模型与单相流的各项同性和各向异性双重孔隙介质流固耦合理论模型进行了比较。     

Investigation on Heat Transfer Properties of Supercritical Water in a Rock Fracture for Enhanced Geothermal Systems

Supercritical water (SCW) has shown promise as a working fluid to extract heat from hot dry rock (HDR); however, fundamental research on its heat transfer characteristics in HDR fractures is still required. A 2D heat transfer model that considers the variable thermophysical properties was updated to numerically investigate the effects of mass flow rate, thermal reservoir temperature, and fracture aperture size on the heat transfer characteristics of SCW flow through a single HDR fracture. The heat transfer performance of SCW and supercritical CO₂ (scCO₂) was compared under the same conditions. The results indicate that the heat transmission performance of SCW is superior to scCO₂ at high temperature and high pressure. It is essential to synthesize the thermal reservoir temperature and pressure, site conditions, and heat transmission fluids during HDR development.     

A two‐scale approach for fluid flow in fractured porous media

A two‐scale numerical model is developed for fluid flow in fractured, deforming porous media. At the microscale the flow in the cavity of a fracture is modelled as a viscous fluid. From the micromechanics of the flow in the cavity, coupling equations are derived for the momentum and the mass couplings to the equations for a fluid‐saturated porous medium, which are assumed to hold on the macroscopic scale. The finite element equations are derived for this two‐scale approach and integrated over time. By exploiting the partition‐of‐unity property of the finite element shape functions, the position and direction of the fractures is independent from the underlying discretization. The resulting discrete equations are non‐linear due to the non‐linearity of the coupling terms. A consistent linearization is given for use within a Newton–Raphson iterative procedure. Finally, examples are given to show the versatility and the efficiency of the approach, and show that faults in a deforming porous medium can have a significant effect on the local as well as on the overall flow and deformation patterns. Copyright © 2006 John Wiley & Sons, Ltd.     

Comparative Investigation on the Heat Transfer Characteristics of Gaseous $$\hbox {CO}_{2}$$ and Gaseous Water Flowing Through a Single Granite Fracture

\(\hbox {CO}_{2}\) and water are two commonly employed heat transmission fluids in several fields. Their temperature and pressure determine their phase states, thus affecting the heat transfer performance of the water/\(\hbox {CO}_{2}\). The heat transfer characteristics of gaseous \(\hbox {CO}_{2}\) and gaseous water flowing through fractured hot dry rock still need a great deal of investigation, in order to understand and evaluate the heat extraction in enhanced geothermal systems. In this work, we develop a 2D numerical model to compare the heat transfer performance of gaseous \(\hbox {CO}_{2}\) and gaseous water flowing through a single fracture aperture of 0.2 mm in a \(\upphi 50\,\times 50\hbox { mm}\) cylindrical granite sample with a confining temperature of \(200\,^{\circ }\hbox {C}\) under different inlet mass flow rates. Our results indicate that: (1) the final outlet temperatures of the fluid are very close to the outer surface temperature under low inlet mass flow rate, regardless of the sample length. (2) Both the temperature of the fluid (gaseous \(\hbox {CO}_{2}\)/gaseous water) and inner surface temperature rise sharply at the inlet, and the inner surface temperature is always higher than the fluid temperature. However, their temperature difference becomes increasingly small. (3) Both the overall heat transfer coefficient (OHTC) and local heat transfer coefficient (LHTC) of gaseous \(\hbox {CO}_{2}\) and gaseous water increase with increasing inlet mass flow rates. (4) Both the OHTC and LHTC of gaseous \(\hbox {CO}_{2}\) are lower than those of gaseous water under the same conditions; therefore, the heat mining performance of gaseous water is superior to gaseous \(\hbox {CO}_{2}\) under high temperature and low pressure.     

Simulation of the transport and placement of multi-sized proppant in hydraulic fractures using a coupled CFD-DEM approach

The productivity of fractured wells is mainly governed by propped fractures, so it is of significant importance to find out where the injected proppants go during hydraulic fracturing treatments, as this is essential to scheduling proppant injection in fracturing design. Using a coupled CFD-DEM model, the transport and placement of multi-sized proppants in fractures in vertical and horizontal wells were systematically investigated, and the effects of having multi-sized particles relative to uniformly-sized ones on the proppant placement were quantitatively characterized. When a proppant-laden fluid is injected into a fracture in vertical wells, a small proppant bank quickly forms. The injected large and small proppant particles are almost uniformly mixed, with just a small-proppant region at the back side of the bank. In comparison in horizontal wells, a proppant dune first forms near the wellbore in a fracture, and the large proppant particles are more likely to accumulate near the wellbore while the small particles are transported deeper into the fracture. The main transport mechanisms of proppant particles are settlement and fluidization, which cause a three-layer flow pattern (stationary proppant bed, fluidization layer and clean fluid layer) to form. In addition, vortex is also an important proppant transport mechanism, especially in a fracture in horizontal wells, where the vortex drags the injected proppant particles to different locations causing a dual-dune profile. The effect of fracture tip screen-out on the proppant placement was investigated. Screen-out can significantly change the flow field in a fracture and this will subsequently affect final proppant placement. Ultimately, the process of graded proppant injection was realistically modeled, which shows small proppants to be transported deeper into the fracture, while large proppants accumulate near the wellbore.     

Mathematical model of heat and mass transfer in a geothermal reservoir upon extraction of steam and water mixture

A mathematical model of heat and mass transfer in a geothermal reservoir saturated with steam and water mixture upon the extraction of heat carrier through a single well is considered. The exact solution of the time-independent and quasi-time-independent nonlinear problems is obtained. Typical water saturation, temperature, and pressure distributions around a well are shown. Conditions for the regimes of heat and mass transfer, the violation of which leads to the formation of a region saturated with either pure fluid of pure steam, are found. Parametric studies are performed.