考虑表面扩散的页岩气渗透率两区复合解析模型

页岩气是一种以吸附态和游离态为主,赋存于纳米级多孔介质中的一种非常规气藏,其渗流特征较常规气藏存在较大的差异。前人研究表明,页岩气运移过程存在多种渗流机理,主要包括:达西渗流、滑脱效应和扩散。虽然前人对自由气扩散的渗流机理模型进行了大量的研究,但是大多没有考虑吸附气表面扩散对渗流的影响。针对以往研究的不足,该文采用两区复合概念模型,建立了考虑吸附气表面扩散、达西渗流和滑脱效应的气体渗流模型,将吸附气和自由气运动关系利用修正的滑脱速度边界条件进行耦合,采用等值渗流阻力法对气体在纳米孔隙介质中渗流的关键参数―渗透率―进行了深入研究,获得了适用于任意克努森数范围的页岩气渗透率解析模型。通过对不同尺度、不同压力下的储层在考虑表面扩散等多重机制下的渗透率进行了计算并发现:吸附气表面扩散是页岩气渗流的重要机理,其对渗透率的贡献会对页岩气藏储层评价和开发方案制定以及增产改造施工设计产生重要影响。     

仿生非光滑沟槽形状对减阻效果的影响

利用有限体积法对三角形、扇贝形和刀刃形三种仿生非光滑沟槽表面流场进行了数值计算.近壁面区采用B-L两层模型,远离壁面区采用雷诺应力模型.分析了三种沟槽非光滑表面的流场特性,对计算域中心 Z＝3mm平面的速度场和湍流统计量进行了研究,分析了不同沟槽形状对减阻效果的影响,为最佳减阻沟槽设计提供了理论依据.三种沟槽具有相同的特征尺寸,顶点间距 s＝0.1mm,沟槽尖顶到谷底高度 h=0.05mm,与光滑表面相比减阻效果分别为 3.2%、9.1%、9.7%,数值计算结果和风洞与油槽实验结果有较好的吻合.     

双筒水流中单颗粒差异旋转惯性力的数值模拟

在实体模型试验的基础上,采用DPM多相流模型模拟泰勒窝胞试验,并将滑移网格运用于同心双筒旋转水流模拟,对水流中单颗粒的运动进行了数值模拟,探讨了单颗粒的运动特性与受力规律。模拟结果表明:1旋转水流体系中水流速度越小,单颗粒发生离心运动的趋势越明显;2当内筒持续旋转、外筒静止时,差异旋转惯性力在数值上小于离心力,但二者属于同一个数量级且方向相同,单颗粒做离心运动,当内筒持续旋转再静止、外筒静止时,差异旋转惯性力与离心力方向相反,在数值上差异旋转惯性力大于离心力,单颗粒做向心运动;3无论内筒是持续旋转还是先旋转后静止,雷诺数均呈逐渐减小趋势,径向受力影响着单颗粒的运动状态。     

水化硅酸钙纳米颗粒间水特性

C-S-H(calcium silicate hydrate,水化硅酸钙)纳米颗粒(约几十到几百个nm)是硬化水泥浆体纳米层次的重要组成,水分在其中的输移特征对硬化水泥浆体有着极其重要的影响。本文通过理论分析,结合原子力显微镜观测结果,提出了水在C-S-H纳米颗粒簇中流动的控制方程,然后确定了黏滞系数和滑移长度2个参数对控制方程的影响,同时考虑C-S-H纳米颗粒表面的范德华力对周围流体的作用,建立了水在C-S-H纳米颗粒簇中流动的物理模型。研究发现,C-S-H纳米颗粒簇间的流体特性不可忽略,在C-S-H纳米颗粒间水分可进行局部的自由交换,交换的结果可能会导致C-S-H纳米颗粒的堆聚结构产生变化,最终会影响水泥基材料的收缩变形行为。     

基于三维数值模拟分析输水工程取水头部水流特性

通过构建标准k-ε湍流模型、流体体积函数模型,结合有限体积法,在进行输水工程取水头部水流的三维紊流以及水流的高散化计算的基础上,根据"无滑移"边界条件,探究输水工程取水头部水流的复杂流动特性。通过将模拟数据与试验数据对比发现,两组结果相一致。由此可以说明,利用构建数字模型的方式可以准确验证进水口体型的设计,对于相关工程建设而言具有重要的作用及意义。     

分层抽水在大厚度含水层水文地质勘查中的应用

为查明深埋于 240 m 以下总厚度达 660 m 的多个大厚度含水层的渗透系数、涌水量、水质等参数, 基于钻孔 岩心和测井资料划分 6 个抽水试段, 利用分层抽水试验进行取样和计算相关参数。研究表明: 研究区洛河组和环 河组平均渗透系数均为上段小于下段, 同一含水岩组上下段含水层之间几乎没有水力联系; 洛河组上段含水层富 含锶优质淡水资源, 可作为城镇集中水源地的目标开采层, 同时要防止过度开采导致水质变差; 单孔多层段含水 层分层抽水试验不仅可以精确获取大厚度含水层的水文地质参数, 还对厘清含水层间越流关系及合理规划地下水开发 利用具有重要意义。     

软土地基沉降计算中压缩层厚度控制标准分析

压缩层厚度是地基沉降计算的重要参数之一,压缩层厚度确定方法主要有应力控制法和应变控制法两种。采用不同的控制标准,计算结果有很大差异。通过对工程实例的计算,比较了这两种方法计算结果的合理性。并讨论了不同应力比条件下,软土地基总沉降计算值随压缩层厚度的变化规律,最后给出了确定压缩层厚度的建议。     

利用相间滑移考虑固相泥沙沉降效应

现有含沙水流数学模型中通过泥沙沉降速度计入的重力沉降项包含有一定的误差，甚至直接采用静水中泥沙沉降速度代替动水中沉速，这样的近似处理没有真实反映泥沙颗粒与主相水之间“滑移”的时空变化特性。本文基于两相流和泥沙运动力学理论，利用相间滑移考虑固相泥沙的重力沉降效应。     

带翼片侧向流斜板沉淀池内颗粒沉降过程的数值模拟

采用有限体积法研究了带翼片侧向流斜板沉淀池内水流流动的特性,并计算了带翼片与不带翼片斜板内水流的雷诺数,结果表明加入翼片可以明显降低水流的雷诺数,其数值为不带翼片斜板雷诺数的42%,并采用层流模型计算了两种情况斜板内水流的三维流场分布情况.在此基础上考察了加入稀疏颗粒后,颗粒物的运动轨迹,采用DPM模型进行计算,结果表明,加入翼片后颗粒物沉降的路径缩短,有利于固液分离;随着水流速度的增大,颗粒跟随性增强,颗粒物密度(采用1100kg/m3和1 400 kg/m3进行分析)增大,颗粒沉降性也增强.同时大颗粒粒径也有利于沉淀.     

复线桥的巷道效应分析

针对两桥和三桥构成的复线桥,利用数学模型计算了不同桥间距和不同斜流交角情况下复线桥的水流流场,得到修建复线桥后通航净宽的减小值,提出计算净宽减小值的公式。结果表明桥洞长度及桥轴线法向与水流方向的夹角是影响巷道效应的主要因素。     

Seepage model and experiments of drag reduction by nanoparticle adsorption

The hydrophobic nanoparticle （HNP） adsorption is a new technique of drag reduction, which changes the wettability of the porous walls of the core, generates the slip-boundary of the fluid flow and consequently enhances the oil recovery. In the present work, a seepage model with consideration of the slip effect in the micro-channels and the influence of the equivalent pore radius mo- dified by the HNP adsorption is proposed based onthe Darcy＇s law. The permeability of the non-wetting phase in the porous media is calculated according to its dependence on the slip length, while the slip length is determined by a function of the contact angle and the equivalent pore radius. Numerical simulations are performed by use of the COMSOL multiphysics, and an acceptable agreement between experimental and simulation results is achieved （with an error less than 2.5%）. The present model can then be used for the mechanism investigation and the prediction of the oilfield performance.     

SLIP VELOCITY MODEL OF POROUS WALLS ABSORBED BY HYDROPHOBIC NANOPARTICLES SiO2

According to new slip effects on nanopatterned interfaces,the mechanism of enhancing water injection into hydrophobic nanomaterial SiO2 was proposed. When Hydrophobic Nanoparticles(HNPs)are adsorbed on surfaces of porous walls,hydrophobic nanoparticles layers are formed instead of hydrated layer, and slip effects appear on the pore wall when a driving pressure is applied to the rock cores sample. It makes fluid to move more quickly and the flow capacity increases greatly. Experiments on changing wettability of porous walls were conducted, and the phenomenon that porous walls surfaces were adsorbed by nanoparticles was validated with the Environment Scan Electron Microscopy(ESEM). The results of displacement experiments show that flowing resistance is greatly reduced , and water-phase effective permeability is increased by 47 % averagely after being treated by nanofluid. These results indicate that the slip effect may occur on nanoparticle film of porous walls. Based on this new mechanism of enhancing water injection about hydrophobic nanomaterial SiO2,a slip velocity model in uniform porous media was introduced, and some formulas for the ratio of slip length to radius, slip length ,stream slip velocity and flux increment were deduced. and calculated results indicate that the ratio of slip length to radius is about 3.54%-6.97%, and the slip length is about 0.024μm -0.063μm. The proposed model can give a good interpretation for the mechanisms of enhancing water injection with the HNPs.     

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes(SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse(i.e., high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT-nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT-nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps.     

低渗透油藏中水平井两相渗流分析

大量实验表明，在低渗透多孔介质中，渗流不再符合线性达西定律，而具有启动压力梯度，本文从Buckley-Leverret不混溶两相渗流驱替理论出发，考虑启动压力梯度的影响，对水平井两相渗流进行分析，得到了椭球形边水油藏中水平井定产时的压力分布公式和定压生产时的产量公式，以及饱和度分布公式。经图示分析得出结论：启动压力梯度不仅增大油藏的生产压差，而且使油藏的无水采收率和水驱采收率减少；增大注入量可以降低启动压力梯度对两相渗流的不利影响，从而提高水驱采收率，因此开发含启动压力梯度油藏，应小井距，大流量，大压差进行注水开发；水平井的两相渗流解析解为数值模拟中水平井的处理提供很好的方法。     

Analysis of shear rate effects on drag reduction in turbulent channel flow with superhydrophobic wall

We examined the shear rate effect on drag reduction of superhydrophobic surfaces with different slip lengths. For this purpose, turbulent channel flow was considered at the friction Reynolds numbers of Reτ = 180, 395, 500. By using Navier＇s slip condition it is shown that increasing shear rate leads to the greater reduction in drag force and also more reduction occurs in larger slip length. Based on the results, more than 25% drag reduction happens at a friction Reynolds number of Reτ= 500 for slip length of 1 ×10 5 m. The simulation results suggest that reduction in drag force occurs because slip condition reduces the Reynolds stresses, also weakens vorticity filed and the near-wall coherent structures, and therefore turbulence production is decreased.     

双重孔隙介质中水平井两相渗流

本文研究了双重孔隙介质中水平井两相渗流问题,在流线不变的假定下,给出了水驱油二维渗流含水饱和度分布和见水时间公式。由于亲水岩块的吸渗作用,裂缝系统中含水饱和度沿特征线按指数规律下降,从而双重孔隙介质的见水时间较均质介质的较晚,采油量较多。     

THE STRUCTURAL FLOW IN PIPE CONTAINING POROUS MEDIUM SATURATED WITH POWER-LAW FLUID

In this article,the method of volume averaging of flow in porous media and averaging theorem was employed to the Navier-Stokes equations.The total drag force per unit volume was considered as the bulk damping resistance due to the porous structure(i.e.,the Darcy resistance)and the resistance due to the inertia force(i.e.,the Forchheimer resistance),then the Brinkman-Forchheimer extended Darcy model was obtained from average momentum equation.The structural flow in a pipe containing porous medium saturated with power law fluid was applied in the present study.A new theoretical analysis of fully developed non-Darcy flow in a pipe containing a fibrous medium saturated with power law fluid was conducted.Using the integration method,the boundary layer solutions were obtained for flow core velocity and its radius.These theoretical solutions were used to analyze the effects of the Darcy number and inertia parameter on the axial velocity profile in the porous medium pipe.     

Numerical simulation of flow through circular array of cylinders using porous media approach with non-constant local inertial resistance coefficient

Aquatic vegetation zone is now receiving an increasing attention as an effective way to protect the shorelines and riverbeds. To simulate the flow through the vegetation zone, the vegetation elements are often simplified as equidistant rigid cylinders, and in the whole zone, the porous media approach can be applied. In this study, a non-constant inertial resistance coefficient is introduced to model the unevenly distribution of the drag forces on the cylinders, and an improved porous media approach is applied to one circular array of cylinders positioned in a 2-D flume. The calculated velocity profile is consistent with the experimental data.     

MECHANISM FOR VISCOELASTIC POLYMER SOLUTION PERCOLATING THROUGH POROUS MEDIA

The pore throat of porous media is modeled as a constricted channel or expanded channel. The flow of viscoelastic polymer solution in pore throat model is studied by numerical method. Relationship between pressure drop and flow rate is developed,viscoelasticity and throat size are found to be two main factors in high flow resistance. According to pore throat model,2-D stochastic channel bundle is put forward to model porous media,which is composed of pore throat models in series -parallel connection with size and length accord to Haring -Greenkorn stochastic distribution. Percolation model of viscoelastic fluid is developed on the basis of Darcy equation and pressure drop vs. flow rate relation in 2-D stochastic channel bundle. Results indicate that the seepage ability of viscoelastic polymer solution decreases with the increase of viscoelasticity,injection rate,and heterogeneity as well as the decrease of mean pore size of porous media. The high pressure drop of viscoelastic fluid at the connection of pore to throat plays a great role in its anomalous high flow resistance through porous media.