含水合物油包水管道输送体系压力波速研究

考虑水合物的相变、油相的压缩性、频率、虚拟质量力及体系的温度和压力的影响,建立了含水合物油包水体系的压力波速方程.研究结果表明,输送过程中水合物对体系的压力波速影响很大,在水合物分解区域,气体的出现使体系的压缩性大幅增加,压力波速急速降低;反之,在水合物生成区域,体系的压缩性减小,压力波速增大.随油水比、管径、温度的减小,压力波速均呈现减小的趋势;随压力、油相密度增加,压力波速呈现增大趋势;压力及温度通过影响水合物的分解速度,对体系压力波速产生影响.     

大跨越管道油气混输压力波速及响应特性研究

基于双流体模型,利用小扰动理论,提出了油气混输大跨越管道压力波速模型.利用计算机编程对其求解,通过大跨越管道油气混输实例,得到了以下结论:压力波速的变化受气相影响较大,即使少量气体也能在较大程度上影响压力波速,随混输气量增大,压力波速减小,压力响应时间延长;混输低点气体所承受的压力较混输高点大,从而低点处气相压缩系数小,混输低点较混输高点压力波速增大,压力响应时间相应缩短;在输运管道低点处,气体受到极大压缩,压力波速的变化不明显,几乎收敛于恒定值,在混输管道高点处压力波速变化剧烈.     

关井期间连续气侵气泡在井筒的动态运移分析

在停止循环状态关井条件下,由于井筒储集效应的影响,地层气会继续侵入井筒,侵入气体沿静止钻井液向上滑脱运移,井口回压与井底压力随之增加,威胁井控安全,因而,有必要研究关井条件下,气泡在井筒内滑脱上升时引起的井口和井底压力波动规律.考虑井筒储集效应,建立了关井期间井底压力和井口压力的计算模型,并对模拟井关井过程中气泡沿井筒运移特性进行了分析.模拟分析结果表明:不同气侵量下,随着关井时间的延长,井底压力和井口压力增加,渗透率低的地层井底压力较高,井口套压稳定的速度较快;当井筒气侵量一定时,随着关井时间的延长,井底压力和井口压力增加,渗透率高的地层井底压力、井口套压较高.     

考虑完井液存在的气井环空带压计算模型研究

准确预测套管内环空压力上升规律有助于指导现场在压力值达到破坏井筒完整性前采取措施,可有效降低环空带压对注采井安全生产带来的威胁.本文考虑气体在完井液中体积变化及运移规律,建立了完井液存在条件下环空压力计算模型,通过对比实例带压井的环控压力计算值与实际值,验证了模型的准确性.同时,计算分析了完井液液柱高度、完井液压缩系数及水泥环渗透率对最大环空压力值与其变化规律的影响,计算结果表明:较大的水泥环渗透率和较小的完井液压缩系数将会增大环空压力的上升速度,而完井液液柱高度不但对环控压力上升速度产生影响,较小的液柱高度还将导致最大环空压力增加.因此,增加完井液压缩性能、适当降低完井液柱高度、提高固井质量以降低气体在水泥环中的窜流是延缓环空带压的有效措施.     

控压钻井井底气侵停止与否实时判别方法研究

实时判别井底气侵停止与否是控压钻井井控方法的关键,直接关系到基于立压控制法循环排气或常规关井等后续作业的选取.综合考虑气体运移膨胀和气体溶解的因素,指出出入口流量一致并不等同于井底气侵停止,两者存在时间先后关系.基于快速施加井口回压控制方法,建立了控压钻井井筒与地层耦合的多相变质量流动模型,采用有限差分法迭代求解,模型计算值与实验测量值吻合较好.模拟结果表明,出口流量有无明显拐点是区分出入口流量一致和井底气侵停止时间先后的标志.一旦井底气侵停止,立管压力的二阶导数会迅速降至0点附近且趋于稳定.根据上述参数变化特征,提出了基于出入口流量和立管压力实时监测的井底气侵停止与否实时判别方法.该研究对于完善控压钻井井控理论具有重要的指导意义.     

基于Hele-shaw模型的斜井偏心环空顶替流体密度差优化

针对斜井中顶替流体密度差及套管偏心引起的顶替界面突进两相流体掺混严重的问题,考虑斜井密度差引起的驱动力沿周向角和半径的变化,建立了斜井偏心环空稳定顶替界面形状模型,利用该模型分析了密度差对顶替界面形状的影响,得到了不同井斜角及套管偏心条件下顶替流体的最优密度差及变化规律:斜井中顶替界面突进的位置及程度取决于套管偏心与密度差的相对作用,存在合理的密度差使得顶替界面长度最短;最优顶替流体密度差随套管偏心度的增加而增大,随井斜角的增大而减小;固井顶替时在满足压稳防漏的条件下直井所选用的密度差越大越好,水平井所选用的密度差应相对最小。     

考虑钻具接头影响的环空压耗计算

控压钻井是针对"窄安全压力窗口"现象所引起的勘探开发过程中的钻井难题所提出的,井筒压力分布的准确预测是保证控压钻井顺利实施的前提,为提高井筒压力的预测精度需准确计算环空摩阻压耗,应用量纲分析理论,综合考虑钻具接头、钻具旋转的影响,修正了环空摩阻压耗计算模型,提高了井筒压力的预测精度.模型研究表明:随着钻井液排量的增加,钻井液从层流变为紊流,局部摩阻压耗明显增加;且井越深,接头的累计压耗越大,接头对总摩阻压耗的贡献增加.随着钻具旋转速度的增加,环空压耗的增加或减少取决于惯性力与剪切稀释的共同作用.     

侵入气体沿井筒的上升规律研究

地层气体侵入井筒后形成气液两相流动体系,气体沿井筒向上滑脱运移,随着所受压力的降低其发展变化过程会很快,如果不及时处理就会演变为井涌、井喷,甚至井喷失控.因此,准确的预测侵入气体沿井筒的上升规律,有助于认识气侵发展过程,同时为现场采取井控措施提供理论依据,有效避免井下复杂事故.基于侵入气体沿井筒运动的力学特性,建立了气体的上升速度模型,模型模拟分析表明:地层渗透率越高、机械钻速越快、单位时间内侵入井筒的气体量越多、气体上升速度越快,井底压力波动越大;施加一定的井口回压可以有效抑制气体的膨胀运移.     

凝析油-气在存在裂缝的双渗介质中渗流的变产量数学模型及其应用

当凝析气藏压力低于露点压力时,有凝析油析出,致使井底附近阻力变大,影响凝析气的采出量,反凝析现象带来了一些特殊的经济问题.选择合理的开发方式,提高凝析气的采收率,成为了当前工作中迫切需要解决的难题.为了控制合理的井底流压常会引起产量的改变.主要针对凝析气在存在裂缝的双渗气藏中的渗流问题,建立气井变产量生产新模型并进行求解,同时选择相关合理参数绘制了试井理论图版,根据试井理论图版利用试井测试数据进行解释,可以得到相应动态参数为气田开发预案提供相应的理论依据.     

一类发烟装液弹装填率的数学模型

装液弹的装填率对弹的安全可靠性极其重要 .如果装液弹的装填率不合理 ,不是造成弹腔容积的浪费 ,就会造成弹内压过大 ,易于破坏密封性能引起渗漏甚至破裂而造成损失和危险 .本文通过对一类发烟装液炮弹弹内压力分析 ,得出了弹内压力计算公式 .在分析压力诸因素时 ,我们运用了固体热膨胀理论 ;考虑了液体的压缩性 .这是本文区别于以往压力计算的两个特点 .通过这类发烟装液炮弹内压压力曲线的分析 ,导出了装液 (炮 )弹弹腔空隙率合理选定最后的数学模型 (PLT方程——可由此确定合理的装填率 ) ,由此所计算的空隙率数据与国外文献值相符 ,并引入了“预极限温度”的概念 .可以相信 ,所谓“预极限温度”,将是装液 (炮 )弹 (或任何装液容器 )设计者必须认真考虑的问题     

Multiphase transient flow model in wellbore annuli during gas kick in deepwater drilling based on oil-based mud

Transient-state gas and oil-based mud (OBM) two-phase flow in wellbore annuli will occur during gas kick. The phase behavior of influx gas and OBM will make the gas kick during OBM drilling more complicated. There are three possible cases in an annulus: only liquid flow in the entire annulus, gas and liquid two-phase flow in part of the annulus, and gas and liquid two-phase flow in the entire annulus. First, the phase behaviors of gas and OBM in wellbore annuli are studied based on the phase behavior of methane and diesel. A multiphase transient-flow model in annuli during gas kick based on OBM is then established based on gas–liquid two-phase flow theory and on flash theory in annuli. The influences of phase behavior in annuli and annular geometry are taken into account. The local flow parameters are predicted by the hydrodynamic models and the local thermodynamic parameters are predicted by the heat-transfer models in the corresponding flow pattern. The proposed model has a better performance, compared with two other models, against the published experimental data. Finally, the variation of pit gain, well-bottom hole pressure, and gas void fraction are obtained, leading to a better understanding of the occurrence and evolution mechanism of gas kick during deepwater drilling.     

Two-fluid and population balance models for subcooled boiling flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in the computer code CFX4.4 is further developed to accommodate the wall nucleation at the heated wall and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Additional comparison using empirical relationships for the active nucelation site density and local bubble diameter is also investigated. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to circumvent the deficiency through the consideration of additional momentum equations or developing an algebraic slip model to account for bubble separation.     

Robertson-Stiff流体在偏心环空中的流动

石油钻井和完井过程中,经常出现泥浆、水泥浆和完井液在偏心环空中的流动。Robertson-Stif流体在描述这些流体的流变性时有很高的精度。文中根据Robertson-Stif流体的流变方程和偏心环空环隙间距的几何关系,利用相似原理,求解了该流体在偏心环形空间中作层流轴向流动时适于工程应用的二元速度分布,以及平均流速、流量和压降的表达式。研究表明:液体在偏心环形空间流动时与在同心环空中流动的最大差异,在于流经偏心环空不同间隙处流速的较大差异。文中还把Robertson-Stif流体的计算结果与采用宾汉模式和幂律模式的计算结果进行了对比。     

Influence of temperature dependent viscosity on peristaltic transport of a Newtonian fluid: Application of an endoscope

The effects of variable temperature dependent viscosity on peristaltic flow of Newtonian fluid in an annulus has been investigated with long wave length approximations. A regular perturbation method has been used to obtain explicit form for the velocity, temperature and relation between flow rate and pressure gradient. The expression for the pressure rise, friction force, velocity and temperature were plotted for different values of variable viscosity parameter β, radius ratio, amplitude ratio ?, heat absorption parameter β₁, and force convection parameter G_r. It is found that the pressure rise decrease as the viscosity parameter β increases and increases as the radius ratio as ? increases and β decreases.     

Analytical estimation of liquid film thickness in two-phase annular flow using electrical resistance measurement

This paper presents an analytical solution to estimate the liquid film thickness in two-phase annular flow through a circular pipe using electrical resistance tomography. Gas–liquid flow with circular gas core surrounded by a liquid film is considered. Conformal mapping is employed to obtain the analytic solution for annular flow with an eccentric circular gas core. The liquid film thickness for an arbitrary annular flow is estimated by comparing the resistance values for concentric and eccentric annular flows. The film thickness estimation has a good performance when the normalized distance between the gas core center and the flow center is less than 0.2 and the void fraction is greater than 0.4, the estimated error of the normalized thickness is less than 0.04.     

Numerical modelling of bubbly flows with and without heat and mass transfer

In this paper, modelling gas–liquid bubbly flows is achieved by the introduction of a population balance equation combined with the three-dimensional two-fluid model. For gas–liquid bubbly flows without heat and mass transfer, an average bubble number density transport equation has been incorporated in the commercial code CFX5.7 to better describe the temporal and spatial evolution of the geometrical structure of the gas bubbles. The coalescence and breakage effects of the gas bubbles are modelled according to the coalescence by the random collisions driven by turbulence and wake entrainment while for bubble breakage by the impact of turbulent eddies. Local radial distributions of the void fraction, interfacial area concentration, bubble Sauter mean diameter, and gas and liquid velocities, are compared against experimental data in a vertical pipe flow. Satisfactory agreements for the local distributions are achieved between the predictions and measurements. For gas–liquid bubbly flows with heat and mass transfer, boiling flows at subcooled conditions are considered. Based on the formulation of the MUSIG (multiple-size-group) boiling model and a model considering the forces acting on departing bubbles at the heated surface implemented in the computer code CFX4.4, comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter, interfacial area concentration, and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Good agreement is achieved with the local radial void fraction, bubble Sauter mean diameter, interfacial area concentration and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress through the consideration of additional momentum equations or developing an algebraic slip model to account for the effects of bubble separation.     

垃圾填埋气体渗流过程中压力分布的滑脱解

考虑气体滑脱效应条件下,建立了垃圾填埋场气体渗流的数学模型．采用摄动法及积分变换法对模型进行解析求解,定量研究填埋气体的压力分布特征,并结合监测数据对模型参数与模型可靠性进行灵敏度分析和验证．结果表明:滑脱效应对气体渗流有较大影响,考虑滑脱效应条件的气体压力小于未考虑滑脱效应条件的气体压力,且得到的滑脱解与实测数值吻合较好．因此,研究填埋气体渗流时不能忽略滑脱效应．这不仅对于填埋场释放气体控制系统的设计和管理提供理论依据,而且可为低渗透油气藏工程开发过程中试井数据的确定提供科学的技术支持．     

Pressure beneath a Stokes wave

We investigate the pressure within an irrotational fluid in a periodic, steady, two‐dimensional gravity wave above a flat bed. We prove that the pressure in the fluid strictly decreases horizontally away from the crest line. Furthermore, the pressure strictly increases with depth. We also investigate the effect of an underlying current on the paths of the particles. © 2009 Wiley Periodicals, Inc.     

The pressure distribution in extreme Stokes waves

In this paper we prove that the pressure beneath an extreme Stokes wave over finite depth is strictly increasing with depth. Additionally it is shown that the pressure decreases in moving between a crest-line and trough-line, while it is stationary with respect to the horizontal coordinate along these lines themselves.     

Direct Resonance of Nonaxisymmetric Disturbances in Pipe Flow

A mechanism which may lead to algebraic growth, followed by exponential decay, of small nonaxisymmetric disturbances in pipe flow is considered. The mechanism is interpreted as a direct resonance between the perturbations of the pressure and the streamwise velocity. The eigenvalue problems for the pressure and the velocity modes have been solved numerically for complex streamwise wave number, and 36 resonances have been investigated. A plot of the propagation speed versus the damping rate shows that the resonances follow certain sequences as the azimuthal wave number increases. The largest propagation speed is found to be ≈ 0.69 times the centerline velocity. No lowest speed is obtained, and as the azimuthal wave number increases the propagation speed decreases. The effects of changing the Reynolds number have also been investigated. It is found that the streamwise wave number and the damping rate are proportional to 1/R as R → ∞. The complex phase speed and the propagation speed become independent of R in the same limit.