Displacement Theory of Low-Tension Gas Flooding

Low-tension gas (LTG) flooding is a promising chemical enhanced oil recovery technique in tight sandstone and carbonate reservoirs where polymer may not be used because of plugging and degradation issues. This process has been the subject of many experimental studies. However, theoretical investigation of the LTG process is scarce in the literature. Hence, in this study, we lay out a displacement theory for LTG flooding, with a constant mobility reduction factor, which lays the groundwork for further theoretical studies. The proposed model is based on the three-phase flow of water, oil, and gas in the presence of a water-soluble surfactant component. Under the developed model, we study the effect of MRF and oil viscosity on the flow dynamics and oil recovery. Moreover, we explain experimental observations on early gas breakthrough that occurs during LTG core floods even in the presence of a stable foam drive.

     

A Comparative Study of Gas Flooding and Foam-Assisted Chemical Flooding in Bentheimer Sandstones

Transport in Porous Media - A laboratory study of principal immiscible gas flooding schemes is reported. Very well-controlled experiments on continuous gas injection, water-alternating-gas (WAG)...     

重力异常对平台式惯性导航系统误差的影响分析

建立了重力异常导致平台式惯性导航系统误差的模型，导出了重力异常东向和北向分量对各个惯导误差量的传递函数，并运用Matlab工具进行了误差仿真，提出了在平台式惯导力学编排中修正重力异常的方案。     

应用PIV技术研究重力式油,气,水分离器的内部流场

重力式油、气、水三相分离器在边际油田开发、处理量不大且油井分布分散的油田开发等方面得到了广泛的应用,文中利用ＰＩＶ技术重点测试分离器内部流场,得到流动死区、旋涡区、流动“短路”等现象,并分析其对分离效率的影响,提出从底部进料、均匀化流速等改进措施．     

The Spreading of Immiscible Fluids in Porous Media under the Influence of Gravity

We use an approach based on invasion percolation in a gradient (IPG) to describe the displacement patterns that develop when a fluid spreads on an impermeable boundary in a porous medium under the influence of gravity (buoyancy) forces in a drainage process. The approach is intended to simulate applications, such as the spreading of a DNAPL in the saturated zone and of a NAPL in the vadose zone on top of an impermeable layer, or the classical problems of gravity underruning and gravity override in reservoir engineering. As gravity acts in a direction transverse to the main displacement direction, a novel form of IPG develops. We study numerically the resulting patterns for a combination of transverse and parallel Bond numbers and interpret the results using the concepts of gradient percolation. A physical interpretation in terms of the capillary number, the viscosity ratio and the gravity Bond number is also provided. In particular, we consider the scaling of the thickness of the spreading gravity tongue, for the cases of gravitydominated and viscousunstable displacements, and of the propagating front in the case of stabilized displacement at relatively high rates. It is found that the patterns have percolation (namely fractallike) characteristics, which cannot be captured by conventional continuum equations. These characteristics will affect, for example, mass transfer and must be considered in the design of remediation processes.     

Analytical Modeling for Gravity Segregation in Gas Improved Oil Recovery of Tilted Reservoirs

Stone’s model for gravity segregation in gas improved oil recovery (IOR) indicates the distance that injected gas and water travel together before the segregation being completed (length of complete segregation). This model is very useful for co-injection of water and gas into horizontal depleted reservoirs. A proof by Rossen and van Duijn showed that Stone’s model applies to steady-state gas–liquid flow, and also foam flow, in horizontal reservoirs as long as the standard assumptions of fractional flow theory (incompressible flow, Newtonian mobilities, local equilibrium) are applied. However, until now, there has been no analytical study on the length of segregation when co-injection of water and gas occurs in tilted reservoirs. In this article, in order to extent the validity of Stone’s model to tilted reservoirs, governing equations of fluids displacement based on fractional flow theory are solved by the method of characteristics, MOC. The results are then compared to Stone’s model and to the results of a three-dimensional finite-difference compositional reservoir simulator. This study shows that Stone’s model should be corrected for tilted reservoirs and that the presented math proof can model gravity segregation in gas IOR of tilted reservoirs, appropriately. The effect of co-injecting of water and gas into tilted reservoirs on recovery efficiency is also examined.     

Magnetic Field Influence on the Gas Detonation Induced by Spark Discharge

The present paper describes the influence of magnetic field on the spark discharge utilized for initialization of detonation. The method of schlieren time-based scanning shows the increase of shock wave velocity in the case when magnetic field was applied to the area of electrical discharge in the air. The critical energy values are obtained for a direct initialization of detonation in hydrogen–air and hexane–air mixtures. Magnetic field has a significant influence on the deflagration–combustion transition in both mixtures at the critical energy values. Pressure and velocity of the shock front were measured by ICP pressure transducers, flame front was recorded by photo-diodes. Two cases were studied experimentally: external magnetic field is produced by inductance coils connected to capacitor; own magnetic field is induced directly by discharge current in the cables positioned in special way.     

均压槽结构形状对静压干气密封性能影响分析

静压干气密封(DGS)中的均压槽起着均布压力和二次节流的作用,开展了典型形状均压槽静压DGS的性能对比和结构优选.基于静压气体润滑理论,建立了圆形、椭圆形、扇形和环形等四种典型均压槽静压型DGS的几何模型和数学模型,采用有限差分法求解获得了四种均压槽静压型DGS端面的膜压分布和稳态密封性能参数,分析了径向开槽比和周向开槽比对四种均压槽静压型DGS密封性能的影响规律;以获得较大的密封开启力和气膜刚度为目标,计算得到了均压槽径向开槽比和周向开槽比的优选值范围.结果表明:当均压槽径向开槽比0.15Wd0.45时,环形均压槽静压型DGS可获得较大的开启力和气膜刚度,其他三种均压槽静压型DGS的径向开槽比优选值范围为0.3Wd0.45;扇形和椭圆形均压槽静压型DGS具有相似的密封性能,其密封性能仅次于环形均压槽静压型DGS;当均压槽周向开槽比0.6Lθ1.0时,扇形均压槽静压型DGS可获得较大的开启力和气膜刚度.     

Problem of Optimal Control of the Turbulent Boundary Layer on a Permeable Surface in Supersonic Gas Flow

The problem of constructing the law of distribution of the normal component of the velocity of blowing to the turbulent boundary layer at supersonic flow velocities which ensure the minimum convective heat flow transmitted from the boundary layer to the surface is considered. The power of the control system calculated with regard to Darcy’s law of flow through a porous medium acts as the isoperimetric condition. The problemis solved using the Dorodnitsyn generalized integral relations. The numerical experiments carried out in the case of flow past a sphere showed the effectiveness of the optimal blowing laws as compared with the uniform law, namely, the gain in the minimized functional reaches 31.82%.     

Influence of Vibrational Relaxation on the Pulsation Activity in Flows of an Excited Diatomic Gas

The influence of vibrational relaxation on the nonlinear evolution of a large vortex structure in a shear flow of a highly nonequilibrium diatomic gas is studied. Calculations are performed using the equations of twotemperature gas dynamics for a viscous heatconducting gas. Relaxation of the temperature of vibrational levels of gas molecules to equilibrium is described by the Landau–Teller equation. The contribution of the relaxation of rotational levels is taken into account by the bulk viscosity in the stress tensor. It is shown that in the presence of only the relaxation process with no viscous dissipation, the damping of the kinetic energy of perturbations and Reynolds stresses increases by up to 10 % compared to the case of thermal equilibrium. For high (actually attainable) degrees of excitation of the vibrational mode, moderate dynamic and bulk viscosities, and a typical relaxation time comparable to flow time, the relative effect of perturbation damping reaches 15%.     

初始压力对多孔介质中气体水合物生成的影响

利用自制的一维天然气水合物生成与开采模拟实验系统,实验研究多孔介质中天然气水合物生成时不同初始压力对生成量、生成时间的影响.分别用相同气水比注入、相同注气量不同注水量、相同注水量不同注气量三种方式来控制初始压力.结果表明:在砂粒粒径300μm～500μm,盐水质量浓度2%,系统温度为2℃、初始压力为5MPa～9MPa的条件下进行水合物的等容生成实验时,初始压力越大,生成的水合物量越多,水合物开始生成的时间越早;但初始压力越大,实验系统中水合物生成最终稳定所需的时间越长.本实验系统采用的三种不同的控制初始压力的方式都可以得到上述结果.由此,可以为今后室内进行天然气水合物的生成实验提供科学指导.     

范德华力对计算机磁头/磁盘超薄气膜承载性能的影响

在纳米间隙条件下,以楔型滑块和双轨式磁头为例,推导出楔型及双轨式磁头范德华力的计算公式,考察了范德华力对计算机磁头/磁盘超薄气膜承载性能的影响.结果表明,范德华力对计算机磁头/磁盘的承载性能影响很大,范德华力可以降低磁头的承载能力,尤其在最小空气间隙小于6 nm时;在相同尺寸的磁头中,双轨式磁头的范德华力小于楔型滑块的范德华力,而前者的承载力大于后者,双轨式磁头的范德华力对其承载性能影响较小.范德华力可以使飞行高度降低,为磁头设计和磁头/磁盘装配的重要依据.     

锌空电池气体扩散电极浸液量对放电性能的影响

锌空电池气体扩散电极在存放和放电过程中,电解液会在毛细力的作用下不断浸入电极。电解液在气体扩散电极中的浸入量与分布情况决定了气体扩散电极中的化学反应活化区,从而影响放电性能。通过实验测量了气体扩散电极开始浸液的4天内浸液量与放电性能的关系,并借助拓扑网络数值模拟电解液浸入多孔介质的过程帮助理解该实验现象。结果表明,随着放电过程的进行,浸液量和分布情况不断变化;气体扩散电极放电性能变化主要分为3个阶段:浸液饱和度为39.4%时放电性能最佳;浸液开始2~24小时进行迅速,浸液饱和度达到81%,放电性能小幅下降;24小时之后浸液增速大幅减缓,放电功率随浸液量增加大幅下降。     

点火能对预混气体爆炸过程及管道薄壁加载响应的影响

在两端封闭的无缝不锈钢管道中,利用压力传感器、应变片以及数据采集系统实验测试了不同点火能作用下,管道内甲烷-空气预混气体爆炸波发展规律及由此造成的管道外壁的动态响应。结果表明,点火能量越大,爆炸反应程度越剧烈,管道内最大爆炸压力就越大,管道薄壁的最大动态应变也越大,爆炸波发展就越迅速,并且管壁动态应变信号和压力波信号出现较好的一致性。本文结果可为油气长输管道的爆炸破坏效应研究提供一种新的思路和方法。     

Influence of Considering the Sorption Effect in the Betti-Maxwell Reciprocal Theorem on Gas Transport Capacity in Unconventional Reservoirs

Transport in Porous Media - Pore bulk modulus in continuum apparent permeability models was generally treated as an independent parameter or deduced from the Betti-Maxwell reciprocal theorem...     

Influence of Microcracks on Flow and Storage Capacities of Gas Shales at Core Scale

Transport in Porous Media - This work investigates the interplay of gas transport in the microcracks and matrix of shale using He and $$\hbox {CO}_2$$ via transient upstream pressure-pulse-decay...     

Gas Injection in a Liquid Saturated Porous Medium. Influence of Gas Pressurization and Liquid Films

We study numerically and experimentally the displacement of a liquid by a gas in a two-dimensional model porous medium. In contrast with previous pore network studies on drainage in porous media, the gas pressurization is fully taken into account. The influence of the gas injection rate on the displacement pattern, breakthrough time and the evolution of the pressure in the gas phase due in part to gas compressibility are investigated. A good agreement is found between the simulations and the experiments as regards the invasion patterns. The agreement is also good on the drainage kinetics when the dynamic liquid films are taken into account.     

Influence of Property Variation on Natural Convection in a Gas Saturated Spherical Porous Annulus

The present study reports results of numerical investigation of natural convection in a spherical annulus filled with gas saturated porous medium. Boussinesq approximation has been relaxed considering variation of density, viscosity, and thermal conductivity of the gas with temperature. The momentum and energy equation along with boundary condition and property variation equations are solved by employing successive accelerated replacement scheme. There exists a reference parameter (q = 0.4) at which if thermo physical properties are evaluated, the average Nusselt number values for variable properties and constant properties are nearly same. Also, the effect of variable properties is negligible for temperature difference ratio, \(\theta ^{*}<0.1\) .