一种考虑虚拟质量力的井筒气液两相压力波色散经验模型

考虑虚拟质量力、管道特性、频率、空隙率等因素,建立气液双流体压力波速模型,结合小扰动理论,提出了一种新的考虑虚拟质量力的两相压力波色散经验模型,与前人气液两相流（12.5%空隙率）中波色散实验测试数据对比是一致的,且经验公式也可达到准确求解压力衰减系数的目的．对控压钻井两相压力波进行计算,结果表明：(1)随系统压力的增大,压力波衰减系数呈现减小趋势,随节流阀动作频率增大、温度增大,压力波衰减系数呈现增大趋势;(2)随空隙率增大,压力衰减呈现先增大后减小趋势,空隙率在8%≤φ≤40%区间,两相压力衰减系数存在最大峰值,当压力为0.2 MPa时,空隙率在19.5%时达到峰值2.78 dB/m;(3)在低频下,波色散主要受相间机械及热力学平衡机制的制约,波色散现象明显;在高频下,相间来不及进行动量及能量交换,气液状态达不到有序的状态,因而波色散现象不明显;(4)不考虑虚拟质量力,两相压力衰减系数呈现增大趋势,波色散现象显著性下降．     

一种考虑虚拟质量力的两相压力波速经验模型

前人建立的两相压力波速经验模型未考虑虚拟质量力,本文考虑虚拟质量力、管壁弹性、管壁粗糙度等因素,通过求解双流体模型的小扰动,提出了一种新的气液两相压力波速经验模型．以一个具体的工程实例为背景,运用数值方法对其求解,得到的计算结果与前人实测的实验数据一致．结果表明,当空隙率较小时(0＜Φ＜15%)时,虚拟质量力对压力波速的影响不大,当空隙率较大时(Φ≥15%),考虑虚拟质量力计算的压力波速远大于不考虑虚拟质量力计算的压力波速．经验公式也可达到准确求解压力波速的目的．     

控压钻井中三相流体压力波速传播特性

考虑虚拟质量力、相间阻力、气相溶解度及滑脱速度等因素,在双流体模型基础上,建立了控压钻井中油-气-钻井液三相流体压力波速模型. 将溢流气体视为气相,将溢流油相及钻井液相视为液相,液相弹性模量及密度等参数为油相及钻井液相中各参数的加权和,利用半隐式差分及小扰动理论等数学方法,借助计算机编程对其求解. 结果表明,当井底气侵量从0.36m3/h 增至3.6m3/h,波速减小峰值为498.59m/s,而相同的油侵增加量,波速呈缓慢减小趋势,波速减小峰值为19.21m/s;当回压从0.1MPa 增至9.0MPa,波速呈增大趋势,波速增大峰值为233.15m/s;不考虑虚拟质量力,在低频段引起的波速误差呈增大趋势,在高频段引起的波速误差峰值稳定于10.03%.      

RESEARCH ON PRESSURE WAVE PROPAGATION CHARACTERISTICS IN THREE-PHASE FLOW DURING MANAGED PRESSURE DRILLING

考虑虚拟质量力、相间阻力、气相溶解度及滑脱速度等因素,在双流体模型基础上,建立了控压钻井中油-气-钻井液三相流体压力波速模型. 将溢流气体视为气相,将溢流油相及钻井液相视为液相,液相弹性模量及密度等参数为油相及钻井液相中各参数的加权和,利用半隐式差分及小扰动理论等数学方法,借助计算机编程对其求解. 结果表明,当井底气侵量从0.36m³/h 增至3.6m³/h,波速减小峰值为498.59m/s,而相同的油侵增加量,波速呈缓慢减小趋势,波速减小峰值为19.21m/s;当回压从0.1MPa 增至9.0MPa,波速呈增大趋势,波速增大峰值为233.15m/s;不考虑虚拟质量力,在低频段引起的波速误差呈增大趋势,在高频段引起的波速误差峰值稳定于10.03%.     

控压钻井气-钻井液两相压力衰减影响因素分析

考虑虚拟质量力、相间阻力、气相溶解度和滑脱速度等因素,在双流体模型基础上,建立了控压钻井气-钻井液两相流动中的压力衰减模型,借助小扰动理论和半隐式差分等数学方法,对其进行编程求解。结果表明:随着温度的增大,压力衰减系数呈线性增大趋势;随着压力的增大,压力衰减系数与压力呈反比例函数趋势;随着空隙率增大,压力衰减系数呈先增大后减小的抛物线趋势。当φg≈21%时,压力衰减系数达到最大值,当p=0.1MPa时,最大压力衰减系数可达2.32dB·m~(-1)。在低频段(w≤50Hz),压力衰减系数随频率逐渐增大;在高频段(w500Hz),压力波的色散性基本不存在,压力衰减系数趋于恒定值。不考虑虚拟质量力的压力衰减系数最大误差达3.09dB·m~(-1),不考虑拖拽力的压力衰减系数最大误差达1.13dB·m~(-1)。     

控压钻井环空卡森流体两相螺旋流轴向速度研究

考虑控压钻井环空气液两相流参数、钻井液周向与轴向运动等因素,本文提出了控压钻井环空卡森流体两相螺旋流柱坐标理论模型;通过新疆玛湖油田区块具体实例,分析了摩阻压降、屈服应力、环空外径、空隙率等对控压钻井两相螺旋流轴向速度的影响。结果表明:控压钻井环空卡森流体两相螺旋流流核及流速峰值向钻杆壁面靠近,距离环空内壁与钻杆外壁中心点的偏度可达8.36%;由于柯特流及钻井液动粘切力下降的影响,随杆转速和管径增大,卡森流体最大速度峰值在轴向的分布向环空壁面移动;随屈服应力的增大,流核宽度呈现增大趋势,当钻井液屈服应力为1.9Pa时,卡森流体流核宽度约为19.3mm;随控压钻井环空内空隙率增大,气液两相的粘度下降,螺旋流的轴向速度峰值呈增大趋势。分析螺旋流轴向速度分布可为控压钻井井口回压加载及环空流速控制提供帮助。     

气液两相流压力波传播速度研究

将双流体模型用于绝热无相的管道气液两相流,依据小扰动线化分析原理,导出了压力波波数Ｋ方程通过对不同空隙率下肉体上压力波小随角频率变化的计算,研究了虚拟质量力和狭义相间阻力对压力波波速及其人色散性的影响。对泡状流和弹状流压力波波速的计算结果与前人的测量结果作了比较,两者符合良好。     

深井气侵关井引发的井筒多相水击压力特性研究

结合小扰动理论,建立了深井气侵关井引发的井筒多相水击压力模型。利用有限体积及特征线等数学方法,提出了基于离散网格求解井筒多相水击压力方法。结果表明:气侵量、井深及关井时间等参数均对井筒多相水击压力影响显著;井底气体的侵入,大幅降低了环空压力,增大了井筒空隙率,减小了井筒水击波速,延缓了井底水击压力峰值点出现时间;随井底气侵量增大,井筒多相水击压力呈减小趋势,气侵量从1.46m3/h增至4.14m3/h,水击压力高峰值大幅度降低;随井深增大,水击压力呈减小趋势,井深1550m同井口处相比,水击压力高峰值减小86.63%;随关井时间延长,水击压力呈减小趋势,关井时间延长10s,水击压力高峰值减小44.46%。     

两相临界流

由于两相临界流在压水反应堆安全分析中的重要性，在过去的４０年内，两相临界流一直是一个活跃的分支学科。本文对压水堆失水事故常用的两相临界流均匀平衡模型、滑移模型、考虑相间热力学非平衡效应的简化模型及两流体模型做了综述。结论是到目前为止，没有一个数学模型能准确预测各种参数范围、各种通道形状的临界流量。特定的模型只能适用于特定的情况。本文对非平衡两相流中汽泡成核、汽泡生长、相界面间质量、动量、能量交换的机理给予了更多的关注。     

基于FSI的4-方程模型的改进分析

传统水击理论所用的连续方程未能反映水击发生时管道内存在的液体压力波速、管道应力波速、流体波速,且进行了大量的简化却不能更好地反应管道系统的实际运动状态。本文主要基于现有的水击计算理论及其耦合理论,在考虑管道纵横两个方向都反映水击耦合特性的情况下,利用特征线法,求出耦合波速;并在推导新的连续方程时将求出的耦合波速替代推导传统4-方程模型的连续性微分方程时水击波速与流速的关系,得到新的连续方程;并忽略高次微量和压力梯度等对新的连续方程进行一定简化,与简化后的流体动量方程、管道运动方程和物理方程构成了改进的轴向4-方程模型。将改进模型求解出的耦合波速与经典模型的进行比较,结果表明两耦合波速相近,但改进模型在考虑管道纵横两个方向都反映水击耦合特性的因素后,理论上会更严瑾、更合理。     

Propagation of a pressure wave in two-phase flow with very high void fraction

An experimental and theoretical study of a finite amplitude pressure wave propagating through a two-phase media of about 0.9999–0.99999 void fraction is performed. This two-phase media consists of many parallel liquid films in a gas. The films are perpendicular to the wave propagation direction and result in a two-phase fluid of extremely high void fraction. Experiments are done in a vertical shock tube and show that the shock wave is broken down into an initial sharply rising wave and a second gradually rising wave. The velocity of the first wave agrees well with the theoretical prediction assuming an adiabatic thermal equilibrium change, which approaches the gas sonic velocity in the two-phase flow in the low void fraction region. The second wave is caused by the complex reflection and destruction of the waves.     

Numerical simulation of circulation in gas-liquid column reactors: isothermal, bubbly, laminar flow

The gas-liquid flow inside a circular, isothermal column reactor with a vertical axis has been studied using numerical simulations. The flow is assumed to be in the laminar, bubbly flow regime which is characterized by a suspension of discrete air bubbles in a continuous liquid phase such as glycerol water. The mathematical formulation is based on the conservation of mass and momentum principle for the liquid phase. The gas velocity distribution is calculated via an empirically prescribed relative velocity as a function of void fraction. The interface viscous drag forces are prescribed empirically. For some cases a profile shape is assumed for the void ratio distribution. The influence of various profile shapes is investigated. The results are compared with those where the void ratio distribution is calculated from the conservation of mass equation. The mathematical model has been implemented by modifying a readily available computer code for single-phase newtonian fluid flows. The numerical discretization is based on a finite volume approach. The predictions show a good agreement with measurements. The circulation pattern seems not to be so sensitive to the actual shape of the void fraction profiles, but the inlet distribution of it is important. A significantly different flow pattern results when the void fraction distribution is calculated from the transport equation, as compared to those with a priori prescribed profiles. When the void fraction is uniformly distributed over the whole distributor plate, no circulation is observed. Calculations also show that even the two-phase systems with a few discrete bubbles can be simulated successfully by a continuum model.     

Propagation of pressure waves in two-phase flow

We deal with a pressure wave of finite amplitude propagating in a gas and liquid medium or in the fluid in an elastic tube. We study the effects of pipe elasticity on the propagation velocity of the pressure wave. Pressure waves of finite amplitude progressing in the two-phase flow are treated considering the void fraction change due to pressure rise. The propagation velocity of the two-phase shock wave is also investigated, and the behavior of the reflection of the pressure wave at the rigid wall is analyzed and compared to that in a pure gas or liquid. The results are compared to experimental data of a pressure wave propagating in the two-phase flow in a vertical shock tube.     

Fluid-solid coupling model for studying wellbore instability in drilling of gas hydrate bearing sediments

As the oil or gas exploration and development activities in deep and ultra- deep waters become more and more, encountering gas hydrate bearing sediments （HBS） is almost inevitable. The variation in temperature and pressure can destabilize gas hydrate in nearby formation around the borehole, which may reduce the strength of the formation and result in wellbore instability. A non-isothermal, transient, two-phase, and fluid-solid coupling mathematical model is proposed to simulate the complex stability performance of a wellbore drilled in HBS. In the model, the phase transition of hydrate dissociation, the heat exchange between drilling fluid and formation, the change of mechanical and petrophysical properties, the gas-water two-phase seepage, and its interaction with rock deformation are considered. A finite element simulator is developed, and the impact of drilling mud on wellbore instability in HBS is simulated. Results indicate that the re- duction in pressure and the increase in temperature of the drilling fluid can accelerate hydrate decomposition and lead to mechanical properties getting worse tremendously. The cohesion decreases by 25% when the hydrate totally dissociates in HBS. This easily causes the wellbore instability accordingly. In the first two hours after the formation is drilled, the regions of hydrate dissociation and wellbore instability extend quickly. Then, with the soaking time of drilling fluid increasing, the regions enlarge little. Choosing the low temperature drilling fluid and increasing the drilling mud pressure appropriately can benefit the wellbore stability of HBS. The established model turns out to be an efficient tool in numerical studies of the hydrate dissociation behavior and wellbore stability of HBS.     

Numerical and experimental study on parameters distribution inside a two-phase ejector

The two-phase flow process in an ejector was numerically and experimentally studied using R141b as a working fluid. A modified one-dimensional gas–liquid ejector model was proposed to remedy the defect in the traditional one. Gas–liquid boundary layer regions were discussed and used to close the model. Mac Cormack method is used to discrete controlling equations of gas–liquid two-phase flow in the ejector. The radial distribution of velocity and temperature, the variation of void fraction, the axial velocity variation and the influence of primary steam pressure on the mixing process were predicted with the numerical model. An experimental rig was set up to validate the model by comparing the experimental pressure distribution in the ejector with the calculating one.     

Mechanism on lateral distribution of small bubbles in?vertical bubbly upflows

The void fraction profile and distributing mechanism of small bubbles were investigated in detail by using the Euler?CLagrange two-way model. The continuous phase is simulated by using direct numerical simulations in Euler frame of reference. Bubble trajectories are tracked by solving the Newton equations of motion with considering forces including gravity force (buoyant force), drag force, lift force, wall lift force, pressure gradient force, virtual mass force, and inertia force in Lagrange frame of reference. Results show that the void fraction profile of small bubbles exhibits double peak values, which is caused by different interphase forces dominating over bubble movements at different bubble places, and paths of bubbles are directly related to their injection places.