Experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering boundary effect

The boundary condition is a crucial factor affecting the permeability variation due to suffusion.An experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering the boundary effect is conducted,where the hydraulic head difference(DH)varies,and the boundary includes non-loss and soil-loss conditions.Soil samples are filled into seven soil storerooms connected in turn.After evaluation,the variation in content of fine sand(ΔR_(f))and the hydraulic conductivity of soils in each storeroom(C_(i))are analyzed.In the non-loss test,the soil sample filling area is divided into runoff,transited,and accumulated areas according to the negative or positive ΔR_(f) values.ΔR_(f) increases from negative to positive along the seepage path,and Ci decreases from runoff area to transited area and then rebounds in accumulated area.In the soil-loss test,all soil sample filling areas belong to the runoff area,where the gentle-loss,strengthened-loss,and alleviated-loss parts are further divided.ΔR_(f) decreases from the gentle-loss part to the strengthened-loss part and then rebounds in the alleviated-loss part,and C_(i) increases and then decreases along the seepage path.The relationship between ΔR_(f) and Ci is different with the boundary condition.Ci exponentially decreases with ΔR_(f) in the non-loss test and increases with ΔR_(f) generally in the soil-loss test.

An analytical transient coal permeability model:Sorption non-equilibrium index-based swelling switch

Long-term permeability experiments have indicated that sorption-induced swelling can switch from internal to bulk depending on the evolutive sorption status.However,this sorption swelling switch mechanism has not been considered in current analytical permeability models.This study introduces a normalized sorption non-equilibrium index(SNEI)to characterize the sorption status,quantify the dynamical variations of matrix swelling accumulation and internal swelling partition,and formulate the sorption swelling switch model.The incorporation of this index into the extended total effective stress concept leads to an analytical transient coal permeability model.Model results show that the sorption swelling switch itself results in the permeability switch under stress-constrained conditions,while the confined bulk swelling suppresses the permeability recovery to the continuous reduction under displacement-constrained conditions.Model verifications show that current experimental observations correspond to the early stages of the transient process,and they could be extended to the whole process with these models.This study demonstrates the importance of the sorption swelling switch in determining permeability evolution using simple boundary conditions.It provides new insights into experimentally revealing the sorption swelling switch in the future,and underscores the requirement of a rigorous model for complex coupled processes in large-scale coal seams.

Analytical solution of a double moving boundary problem for nonlinear flows in one-dimensional semi-infinite long porous media with low permeability

Based on Huang＇s accurate tri-sectional nonlin- ear kinematic equation （1997）, a dimensionless simplified mathematical model for nonlinear flow in one-dimensional semi-infinite long porous media with low permeability is presented for the case of a constant flow rate on the inner boundary. This model contains double moving boundaries, including an internal moving boundary and an external mov- ing boundary, which are different from the classical Stefan problem in heat conduction： The velocity of the external moving boundary is proportional to the second derivative of the unknown pressure function with respect to the distance parameter on this boundary. Through a similarity transfor- mation, the nonlinear partial differential equation （PDE） sys- tem is transformed into a linear PDE system. Then an ana- lytical solution is obtained for the dimensionless simplified mathematical model. This solution can be used for strictly checking the validity of numerical methods in solving such nonlinear mathematical models for flows in low-permeable porous media for petroleum engineering applications. Finally, through plotted comparison curves from the exact an- alytical solution, the sensitive effects of three characteristic parameters are discussed. It is concluded that with a decrease in the dimensionless critical pressure gradient, the sensi- tive effects of the dimensionless variable on the dimension- less pressure distribution and dimensionless pressure gradi- ent distribution become more serious; with an increase in the dimensionless pseudo threshold pressure gradient, the sensi- tive effects of the dimensionless variable become more serious; the dimensionless threshold pressure gradient （TPG） has a great effect on the external moving boundary but has little effect on the internal moving boundary.

Effect of absorption boundary layer on nonlinear flow in low permeability porous media

Taking low permeability cores of Daqing oilfield for example,the flow characteristics at low velocity were studied with the self-designed micro-flux measuring instrument.Considering the throat distribution and capillary model,the thickness of fluid boundary layer under different pressure gradients was calculated,and the mechanism and influencing factors of nonlinear percolation were discussed.The results show that the percolation curve of ultra-low rocks is nonlinear,and apparent permeability is not a constant which increases with pressure gradient.The absorption boundary layer decreases with the increase of pressure gradient,and changes significantly especially in low pressure gradient,which is the essence of nonlinear percolation.The absorption boundary layer is also found to be impacted by the surface property of rocks.

Semi-analytical solutions to one-dimensional consolidation for unsaturated soils with semi-permeable drainage boundary

The semi-analytical solutions to Fredlund and Hasan＇s one-dimensional （1D） consolidation for unsaturated soils with a semi-permeable drainage boundary are pre- seated. Two variables are introduced to transform the two coupled governing equations of pore-water and pore-air pressures into an equivalent set of partial differential equations （PDFs）, which are easily solved by the Laplace transform method. Then, the pore-water pressure, pore-air pressure, and soil settlement are obtained in the Laplace domain. The Crump method is adopted to perform the inverse Laplace transform in order to obtain the semi-analytical solutions in the time domain. It is shown that the proposed solutions are more applicable to various types of boundary conditions and agree well with the existing solutions from the literature. Several numerical examples are provided to investigate the consolidation behavior of an unsaturated single-layer soil with single, double, mixed, and semi-permeable drainage boundaries. The changes in the pore-air and pore-water pres- sures and the soil settlement with the time factor at different values of the semi-permeable drainage boundary parameters are illustrated. In addition, parametric studies are con- ducted on the pore-air and pore-water pressures at different ratios （the air permeability coefficient to the water permeability coefficient） and depths.

Simultaneous inversion of permeability,skin and boundary from pressure transient test data in three-dimensional single well reservoir model

This study presents a novel approach for simultaneous inversion of the key reservoir parameters like horizontal permeability,vertical permeability,skin,and boundary distances for spatial distribution across the grid cells in a 3D single well reservoir model(SWRM).These parameters are first estimated from the standard pressure transient analysis of well test pressure and rate data,which also act as a priori for the inverse problem.A field-worthy layer cake geological model is prepared based on the prior information obtained from pressure transient analysis,followed by a sequential flow simulation of field well test operation.The simulation results provide the model pressure versus rate data as the synthetic data for this study.A cost function is defined incorporating the well test pressure data and model pressure data,which would determine the convergence.The inversion process is to optimize the spatial distribution of reservoir parameters to minimize the difference between the measured pressure transient data and the modelled one,which is obtained from the multiphase fluid flow simulator that solves the implicit black-oil fluid-flow diffusivity equations at every step.A Gauss-Newton(GN)inversion scheme is used for the inversion.The reliability of inversion results depends on the accuracy of priori reservoir parameters fed to the solver,which can be refined if required through uncertainty parameter optimization(UPO).This approach helps to obtain a faster and reliable update of reservoir parameters in a layer cake homogeneous geomodel,hereby introducing the required heterogeneity.This increases the confidence and reliability of a geomodel,which is further used for various production prediction strategies.

不同透水条件下海底饱和沉积层动力响应特性分析

海床沉积层的透水条件可以直接影响其在地震中的动力响应特性,但是在现有的理论研究中,大部分都直接假设海床沉积层的底部为不透水边界。为此,基于Biot饱和多孔介质理论,通过求解沉积层瞬态响应和稳态响应的解析解或半解析解,研究了沉积层底部透水条件对其在地震中动力响应特性的影响。研究结果表明,在底部位移激励的条件下,快波和慢波经过沉积层的不透水底部边界时会产生一类压缩波,经过沉积层完全透水底部边界时会产生两类压缩波;即使在相同的激励条件下,不同透水性能的沉积层中产生的两类压缩波的振动幅值也具有非常显著的差异;沉积层底部透水条件也会影响海床的频率响应特性,低频时底部透水的沉积层的位移放大系数较大;相反,高频时底部不透水的沉积层的位移放大系数较大。

岩心油水两相渗流启动压力梯度实验研究

低渗储层油水两相渗流时存在启动压力梯度,充分认清水驱油时启动压力梯度的变化和影响因素对油藏水驱开发至关重要。为了搞清油藏储层油水两相渗流启动压力梯度特点及其影响因素,对不同渗透率、不同含水饱和度、不同润湿性岩心水驱油两相渗流的启动压力梯度进行了室内实验测定,根据实验现象和实验结果,分析了产生启动压力的岩心孔隙内部的阻力效应和微观成因。研究结果表明:气体渗透率小于50×10^(-3)μm^(2)的低渗岩心随含水饱和度增加,启动压力梯度增大;气体渗透率大于50×10^(-3)μm^(2)的中高渗岩心启动压力梯度随含水饱和度变化不大,总体呈下降趋势,且数值较小;对于低渗油藏,启动压力梯度随岩心渗透率降低而增大,随岩心润湿指数增加而减小;岩心边界层液体厚度越大,启动压力梯度越大。产生启动压力的附加阻力效应有油滴毛管力产生的摩擦阻力、静润湿滞后导致油珠变形产生的阻力及液阻效应产生的阻力,其大小和岩石孔喉半径、润湿指数、微观孔隙的油水分布状态、边界层厚度及固液界面张力有关。

基于广义Voigt模型的半渗透边界隧道周围饱和软土固结分析

引入衬砌半渗透边界条件,使用广义Voigt黏弹性模型描述隧道周围饱和软黏土的流变特性,基于Terzaghi-Rendulic理论建立以超孔隙水压力为变量的软土二维流变固结控制方程。采用保角变换和分离变量方法,得到超孔隙水压力关于时间和空间变量的两个独立方程,依次使用Laplace变换法与部分分式展开法得到时域内超孔隙水压力消散解。将广义Voigt模型退化为已有四元件Burgers模型和五元件模型并与其对比,验证解答的可靠性。基于建立的解答,分析衬砌透水程度、Kelvin体数量、独立Newton黏壶黏滞系数、隧道埋深等因素对超孔隙水压力消散与分布的影响规律。结果表明:衬砌与土体的相对渗透系数比越大,超孔隙水压力的消散起始时间越早,消散速度越快。Kelvin体数量越多,超孔隙水压力消散越慢;独立黏壶黏滞系数越大,其产生的黏滞变形越小,超孔隙水压力消散速率越快;隧道埋深越大,土体渗流路径越长,超孔隙水压力消散越慢;当相对渗透系数比为0.01时,超孔隙水压力随着到隧道外壁距离的增大而逐渐减小,当相对渗透系数比为1.00时,超孔隙水压力随着距离的增大而出现先增大后减小的现象;随着相对渗透系数比的增加,Kelvin体数量对超孔压消散的影响越小,不同独立黏滞系数带来的超孔压消散差异逐渐减小,隧道衬砌作为土层内部新透水边界的作用越突出。

考虑混合润湿孔隙的页岩油藏表观渗透率模型

页岩油藏是典型的非常规油气资源,在国际能源供应市场上占有重要地位。由于页岩油藏复杂的孔隙结构和原油组成,使得原油在富有机质页岩中的流动具有一定的复杂性,对其流动行为仍有待进一步深入研究。基于随机模拟方法,考虑流体在混合润湿纳米孔隙中的流动特征,建立页岩油藏表观渗透率模型。结果表明:页岩油藏表观渗透率与烷烃分子结构直接相关,其影响随着孔隙半径的增大而减小;当边界滑移长度较大时,有机质的存在可以改善原油流动能力,其表观渗透率约为绝对渗透率的10倍。同时,有机质吸附导致的孔隙半径缩小和润湿反转效应对烷烃分子流动能力有显著影响,不可忽略。所建立的考虑混合润湿孔隙的页岩油藏表观渗透率模型有助于深入认识页岩油藏流体渗流机理,可为页岩油藏产能评价、动态分析及生产制度优化提供理论支撑。

元刻板印象威胁与体育硕士研究生学业成就的关系:学校归属感的中介作用和群体边界渗透性的调节作用

目的:厘定体育硕士研究生学业成就达成的影响因素及其内在作用机制。方法:采用问卷法,对486名体育硕士研究生进行调查研究,考察元刻板印象威胁与学业成就的关系,同时探讨学校归属感的中介以及群体边界渗透性的调节作用。结果:元刻板印象威胁显著负向预测学校归属感(β=-0.36)、学校归属感显著正向预测学业成就(β=0.19);元刻板印象威胁与群体边界渗透性的交互项能够负向预测学业成就、学校归属感(β=-0.10、β=-0.12)。结论:学校归属感在元刻板印象威胁与体育硕士研究生学业成就的关系中起部分中介作用;群体边界渗透性调节元刻板印象威胁通过学校归属感影响体育硕士研究生学业成就这一过程的直接路径和前半路径。

考虑虚拟边界与应力耦合的页岩渗透率模型

为探讨页岩气开采过程中页岩渗透率的变化情况,基于毛细管层序模型,采用虚拟边界与应力耦合相结合的方法,按照一定权重系数将应力推导黏性流动和克努森扩散相加,建立了页岩纳米孔体相气体传输模型。结果表明:新建渗透率模型计算曲线与试验实测值吻合较好,可以较好揭示页岩纳米孔体相气体流动情况;与Lu模型和S&D模型相比,新建模型考虑虚拟边界与应力的耦合,表观渗透率模型计算曲线与试验结果更为吻合,且能很好地反映实测值与孔隙压力所呈现的变化规律,具有较好的优越性;页岩力学参数(弹性模量、泊松比)、Langmuir应变常数及裂隙压缩系数对页岩渗透率起抑制作用,主要表现为其值越大,页岩渗透率越小;初始渗透率对页岩渗透率起促进作用,表现为其值越大,页岩渗透率越大。研究成果可为页岩气开发提供理论支撑。

边水气藏水侵动态分析方法及水侵主控因素

基于经典分流理论与气水渗流规律,推导了考虑气体高速非达西渗流的边水气藏分流方程,并根据四川盆地某边水气藏多口产水气井的基础资料,分析了水侵动态特征参数的变化规律及主控因素,探讨了延缓气藏水侵的技术思路与对策。研究结果表明:(1)新的改进分流方程能够确定不同开发时刻气藏(或气井)边水的整体推进情况及见边水时间,相较于传统的基于达西定律的分流方程,该计算结果更加可靠。(2)边水气藏水侵动态受制于多种因素的综合影响,其中储层渗透率对其影响最为显著,其次为非达西流系数、相对渗透率及孔隙度,而有效厚度、供气边界及水侵流量的影响程度较小。(3)充分发掘物性较均一的低渗致密段储层的开发潜力是提升边水气藏开发效果的关键,制定合理的气藏采气强度是主动控水、稳水的重要手段。

Modflow中关键参数取值对矿井涌水量预测的影响研究

针对鄂尔多斯地区矿井开采过程中的涌水问题,以核桃峪井田为研究对象,对区域水文地质条件进行梳理,确定合理的概念模型和边界范围,建立了Visual Modflow数值模型,应用模型的排水沟边界模块,预测响应工作面采掘进度的矿井涌水量变化。并对排水沟水力传导系数C与含水层渗透系数K两个影响因子进行了不确定性分析,确定C的取值对工作面涌水量预测的影响更显著。根据临近的雅店井田两个工作面实际涌水量对C值进行反演,确定研究区域C值范围并代入核桃峪井田工作面预测中。结果表明:工作面涌水量预测值会随着C值取值增大而增大,当C取值约6.5×10^(-5)时,雅店井田工作面涌水量接近实际涌水量。基于该值计算出核桃峪井田各工作面矿井涌水量情况,待5个工作面回采结束后,矿井涌水量总量达到2697.2 m^(3)/h。

相邻点渗透率级差在储层精细描述中的应用——以惠州凹陷H油田为例

无论储层构型研究还是流动单元分析,界面的识别是关键。相邻点渗透率级差是相邻两个数据点的测井解释渗透率最大值与最小值之比,对于由沉积、成岩作用变化引起的储层孔隙结构和物性变化非常敏感。引入相邻点渗透率级差这一新参数,可有效弥补测井曲线对低级次界面识别能力不足的缺点,提高界面识别的精度,明确3级和5级构型界面的存在及其准确位置,将储层构型研究推向更深层次;利用相邻点渗透率级差进行流动单元的划分,可快速识别流动单元界面,计算流动单元分类的界限值,并明确各类流动单元的地质含义。

低渗透油藏微乳液驱渗流规律研究

主要探索了微乳液驱在低渗透油藏的渗流规律,并研究流体在低渗透介质空隙中的渗流边界体,微乳液驱在改善油气外部环境以及流体的可流动性;分析微乳液在降低界面张力、渗透边界层和启动压力梯度进行理论分析。

Meshless Method for Analysis of Permeable Breakwaters in the Proximity of A Vertical Wall

In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method(BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater's width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.

MHD free convective flow past semi-infinite vertical permeable wall

In this paper, the basic equations governing the flow and heat transfer of an incompressible viscous and electrically conducting fluid past a semi-infinite vertical per- meable plate in the form of partial differential equations are reduced to a set of non-linear ordinary differential equations by applying a suitable similarity transformation. Approx- imate solutions of the transformed equations are obtained by employing the perturbation method for two cases, i.e., small and large values of the suction parameter. From the numerical evaluations of the solution, it can be seen that the velocity field at any point decreases as the values of the magnetic and suction parameters increase. The effect of the magnetic parameter is to increase the thermM boundary layer. It is also found that the velocity and temperature fields decrease with the increase in the sink parameter.

群际边界通透性影响移民偏见的心理机制

在全球化背景下,群际边界通透性对移民偏见的影响颇具热点性和争议性。当前这一领域的研究存在着群际边界通透性增加、减少和不影响移民偏见三种不同结论,然而导致不一致结论背后的心理机制尚不清楚。本文在梳理群际边界通透性对移民偏见影响的基础上,提出了二者之间的作用机制模型。群际边界通透性对移民偏见的影响可能受到内群体、移民和环境等因素的调节作用。此外,群际边界通透性也可能通过影响不同的心理路径,继而对移民产生不同的偏见。对群际边界通透性影响移民偏见心理机制的探讨,对改善群际关系和移民治理工作具有重要的理论和现实意义。

含Bi高磁感取向硅钢二次再结晶前Bi的行为分析

针对高、低温板坯加热0.27 mm厚度含Bi高磁感取向硅钢二次再结晶前不同工序的线切割试样(铸坯、热轧、常化、冷轧、脱碳退火),利用扫描电镜BSE模式对单质Bi颗粒进行观察分析、俄歇电子能谱仪对Bi的分布进行半定量分析。结果表明,钢水中未溶解的Bi会作为单质颗粒呈球形存在于铸坯等不同工序中,脱碳退火后,Bi单质颗粒析出质量百分比达最高。Bi元素偏聚规律在高、低温两种工艺生产的高磁感取向硅钢中基本类似,各工序中均存在比较明显的Bi的晶界偏聚,其中在脱碳退火后,Bi的晶界偏聚相对含量达到最大值。