NUMERICAL SIMULATION OF TRANSIENT CUTTINGS TRANSPORT WITH FOAM FLUID IN HORIZONTAL WELLBORE

With considering the interlayer mass transfer and fluid influx from the reservoir, a one-dimensional two-layer hydraulic model was established to describe the mechanism of transient cuttings transport with foam fluid in horizontal well section. The model was numerically calculated based on the modified SIMPLE algorithm, and the height of cuttings bed was predicted by the trial-and-error method. Sensitivity analysis was conducted on the affecting factors on the cuttings transport performance. Results show that cuttings deposition moves along the horizontal wellbore from the drilling bit, and finally achieves a steady state with dynamic balance. Dimensionless cuttings bed height decreases with the increase of foam quality or foam flow rate, but increases with the increase of drillpipe eccentricity, cuttings size or drilling rate. The influx of water and gas from the reservoir is helpful to improve the cuttings transport efficiency with foam. The proposed model offers theoretical guidelines for hydraulic parameter design and hole cleaning control in foamed horizontal drilling.     

水泥浆流变性分析及其环空流动的数值模拟

偏心环空流动的均匀性在固井工程中有重要影响。通过实验对三种不同配方的水泥浆进行流变性分析,得到适合水泥浆的最佳流变模式是赫切尔一巴尔克莱(H-B)模式。应用Fluent软件对外径0.24 m(9 1/2”),内径0.18 m(7”)的环空井筒内水泥浆流动进行了数值模拟,得到了偏心度、流速以及流体的流变参数对流动不均匀度的影响规律。模拟结果表明,偏心是引起环空流动不均匀的主要原因。随着偏心度的增加,流动均匀性降低;另外,提高流动速率以及降低流体的屈服应力、稠度系数和流性指数有利于环空流动的均匀性。     

Distribution features of cuttings bed and sensitivity analysis of major drilling parameters for cuttings transport in gas drilling horizontal wells

In the current engineering methods for the gas horizontal drilling, the distribution features of cuttings bed remain an issue to be cleared, and the gas horizontal drilling is still in early stages of development. For on-site drilling, a 3-D transient model is established in this paper to simulate the distribution features and the transport mechanism of the cuttings bed, based on the gas-solid two-phase flow theory. The effects of major drilling parameters, such as the gas velocity, the drill pipe rotation, the cutting size and the eccentricity, on the cuttings transport efficiency are analyzed. The major findings of this study include that the cuttings begin to settle down and build up a fixed cuttings bed, in the most evident regions in front and behind the connector, the dominant parameter of the wellbore cleaning is the gas velocity, and, as the cutting size is increased, the thickness of the cuttings bed developed in the wellbore increases significantly. In addition, the eccentricity has some influence on the cuttings transport, and the drill pipe rotation has little effect on the cuttings transport.     

圆柱体绕流环隙流场轴向流速及水力损失试验研究

为进一步完善圆柱体绕流环隙流场理论,采用理论分析和模型试验相结合的方法,对不同流量及环隙比条件下圆柱体绕流环隙流场进行了研究,得出其轴向速度及水力损失随测点距离管道中心距离的变化关系曲线,并给出环隙水流轴向速度及水力损失分布曲线以及随流量及环隙比变化的相关拟合公式。试验结果与拟合公式基本一致,相关系数大部分在0.95以上,说明拟合公式是可行的。试验结果为圆柱体绕流环隙流场理论研究及实际应用提供了支撑。     

多组分流元模型在稀性泥石流堆积分选特征研究中的应用

基于结构两相流模型和PIC数值计算方法，本文探讨了稀性泥石流堆积过程中的泥沙分选特征。文中的模型可以模拟阵性泥沙流的非稳定特性，通过将传统的Euler和Lagrangian方法结合泥沙流运动的整个过程都能够采用多组分流元模型进行很好的描述。该模型也能够合理描述泥沙分选过程中伴随的冲淤过程。文中采用2～5°的坡度，固相颗粒被分为三组粒径不同的组分。研究表明，泥石流的垂向和横向分选都不明显，但是纵向分严为明显。河槽坡度和泥石流的密度是影响泥石流分选过程的两个关键因素。泥沙输移能力越大，颗粒分选越不明显，对泥石流分选特性的定量预测有助于深入了解泥石流的沉积机理和泥石流灾害的防治。     

水平井筒变质量分散泡状流压降的理论与实验研究

由于水平井筒和常规水平管道中气液两相流动的相似和差别，可以预知常规水平管流的压降计算方法对于井筒流动来说就需要进行修正或扩展。本文对气、液两相分别应用质量守恒方程和动量守恒方程，考虑管壁存在人流或出流对于分层流流型压降的影响，得到水平井筒气液两相变质量流动分散泡状流流型的压降计算方法。同时，设计并建立了水平井筒流体流动模拟实验装置，在轴向为气液两相流动的前提下分别进行了上管壁单孔眼注入和下管壁单孔眼注入的压降实验研究，获得了大量的实验数据。实验数据和理论计算结果吻合很好，这表明该计算方法具有实际应用价值。     

压力脉冲在井眼气－液两相流传播的数值模拟

本文对压井期间节流阀调节过程中压力脉冲在井眼环空气－液两相流中传播速度进行了数值模拟。建立并求解了一维拟线性双曲型偏微分方程组，从而能够给出气侵后环空气－液两相流分布和在压井期间的气－液两相流分布。同时导出了压力脉冲在气－液两相流中传播速度公式，给出了计算节流阀调节间隔计算方法。举例计算出了节流阀调节后压力脉冲经过钻柱泥浆及环空流体中传播时间。利用本方法可以适时调节节流问，使压井期间井底保持较恒定的压力，从而真正符合并控理论。     

偏心环空层流螺旋流动的近似解析解

本文分析计算了石油钻井工程偏心环空中内管转动的螺旋流动，将偏心环空的三维流动简化为环空薄层内的二维流动，从黎曼空间曲面张量表达的动量方程出发，求得了偏心环空层流螺旋流动速度的近似解析解。用此方程的同心环空表达式与精确解比较，精度较高。     

承压含水层中“扩展”井附近非达西流数值解

本文采用有限差分方法得到了承压含水层中抽水井附近非达西流的数值解，采用无量纲变量分别分析了考虑井储和不考虑井储影响的水头降深规律，并与Boltzmann变换和线性化方法所得到的近似半解析解进行了比较。结果表明，在不考虑井储影响的情况下, Boltzmann变换解与数值解吻合较好；当考虑井储影响时，Boltzmann变换解存在较大误差；无论考虑井储影响与否，线性化方法所得到的近似半解析解，在抽水后期均与数值解吻合较好，在抽水初期则存在一定误差。同时采用数值解分析了无量纲非达西水力传导度kD对水头降深的影响，在抽水后期，kD越大，水头降深越小。     

SIMULATIONS OF FLOW INDUCED CORROSION IN API DRILLPIPE CONNECTOR

Drillpipe failure is an outstanding issue in drilling engineering, often involving great financial losses. In view of the special features of the flow channel in the high failure zone, this article analyzes the drillpipe failure mechanism from the point of view of flow induced corrosion. Based on the Eulerian-Langrangian method and the discrete phase model, a numerical simulation method is used to investigate the flows of the drilling fluid in the drillpipe connector during the operation of three typical drilling methods (mud drilling, air drilling and foam drilling). From the flow field in the drillpipe connector, especially, the velocity and pressure distributions in the threaded nipple and the thickened intermediate belt, one may detect the existence of the flow induced corrosion. Then, some structural optimization measures for the drillpipe connector are proposed, and the optimization effects are compared.     

水石流的输沙浓度与流动速度

自然界水石流以粗颗粒为主体 ,仍有一部分作悬移运动的细颗粒存在 ,这种情况下 ,水石流输沙浓度不仅与沟道纵坡有关 ,还与细颗粒含量有关。研究表明 ,水石流中细颗粒的存在 ,其输沙浓度比相同纵坡下没有细颗粒时有很大提高。由于水石流中细颗粒所占比重小 ,故其液相流速可以通过对一般水流流速公式的阻力因子进行修正获得。水石流的流速随其浓度增加而减少 ,在相同浓度下 ,水石流流速还因细颗粒含量大小而变化 ,在浓度较低时 (Sv <0 4 5 )影响还不明显 ,在浓度较高时 (Sv>0 4 5 ) ,细颗粒含量增加 ,使同浓度水石流的流动速度提高。笔者求得的水石流流速公式 ,经实际观测资料检验 ,结果满意     

射流清淤对提高潼关河段输沙能力的作用

根据水流输沙机理及潼关河段射流清淤的野外试验资料,分析了影响潼关河段输沙能力的因素及射流船的射流冲刷效果,并初步计算了射流清淤对提高输沙能力的作用。研究认为,潼关河段的射流清淤,一方面通过射流装置冲起大量泥沙,提高了水流的含沙量,另一方面改善了清淤河段的河槽形态,使之趋于窄深,从而提高了河道输沙能力。初步结果表明,射流清淤使河道增加的输沙量是射流冲起泥沙量的1．6倍左右。     

FLUID FLOW IN ROTATING HELICAL SQUARE DUCTS

1 .　INTRODUCTIONTherotatinghelicalsquareducthasextensive lyapplicationsinengineeringforenhancingtheratesofheatandmasstransfer ,suchascoolingsystemsforconductorsofelectric generatormo tors ,gasturbines ,separation processes .Becauseoftherotation ,theCoriolisforcecanalsocontrib utetothe generationofsecondaryflow ,whichcomplicatestheflowcharacteristics .To gethighperformanceofthesedevices,itisimportanttofindouttheflowcharacteristicsinrotatinghelicalsquareducts .Duetothecomplexityoftheproble…     

实体肿瘤不均匀血液灌注对流体流动的影响

由于实体肿瘤结构的复杂性,内部毛细血管分布明显的不均匀性,间质的高阻、高压引起的低对流,使肿瘤的化学治疗药物难以达到靶细胞。本文建立球形实体肿瘤的“毛细血管——毛细血管跨壁交换——间质流动”模型,考察肿瘤内流体的流动。从解剖学出发,引入幂函数、三次多项式、反正切函数等形式的毛细血管密度分布,反映肿瘤内部不均匀的血液灌注,讨论它们对流体流动的影响。根据Starling定律,建立跨毛细血管壁的物质传递模型;间质中的流动由Darcy定律决定,由此得到了离体肿瘤内部压强、流动速度分布。讨论了反映不均匀血液灌注的毛细血管密度分布对实体肿瘤动力学参数影响。结果表明肿瘤内部的高压强和低压强梯度引起的低对流,使药物分布难以达到期望的状态。血管密度分布明显影响肿瘤内物质传递,中心坏死部分越明显,药物越难以进入肿瘤内部。这可以为揭示肿瘤的化学药物治疗中的困难给出有益的提示。     

TWO-PHASE FLOW OF HIGHLY CONCENTRATED SLURRY IN A PIPELINE

Hydraulic transport of sand is one of the key processes in river, lake, harbor and waterway dredging engineering. Understanding the flow resistance, solid distribution, flow stratification, transport economy, etc. , in the twophase flow of sand water mixture through a pipeline is crucial to the design and operation of power drives of a dredger, and to the construction of a dredging project. This paper presents the intensive laboratory experimental data and physical and numerical analyses on the highly concentrated slurry flow under an extended large range of slurry mean velocities for three narrow-graded sands of different sizes. The investigation indicates that the solids concentration and particle size strongly affect the slurry flow characteristics.     

Distribution features, transport mechanism and destruction of cuttings bed in horizontal well

In an effort to develop methods of solving the issue of cuttings bed in horizontal wells, a 3-D transient model is established to simulate the distribution features and the transport mechanism of cuttings bed. The CFD calculation results show that the cuttings at the cross-sectional area of the mutation location such as the drilling pipe connector would easily settle down to build up a cuttings bed and the transport performance of the cuttings in a horizontal well can only be improved to some extent by adjusting the working parameters without using any destruction tools for the cuttings bed, thus the issue of a cuttings bed can not be solved in general. Accordingly, a new approach to effectively prevent and actively destroy the cuttings bed by using the Cuttings Bed Impeller (CBI) is proposed, the sensitivity analysis of which is conducted to determine the optimal structural parameters and the best matched working parameters from a perspective of the wellbore cleaning. Results show that the use of the CBI produces a number of benefits, including the reduced drill string torque to avoid the stuck pipe incidents with corresponding improvement in hole quality, a shorter trip time, and less wear on the drill string, the top drive and the casing. This research offers theoretical guidelines for the design of destruction tools for the cuttings bed and for the wellbore cleaning control in the horizontal drilling.     

THE FLOW IN ROTATING CURVED CIRCULAR PIPE

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从大型实验室波浪泥沙输运实验得到的启示

展示了一些用于测量波浪输沙过程的基本特征的大型实验的关键结果。这些实验是在Delft水力研究所的大型振荡水槽中进行,还有一些是在阿伯丁振荡流隧道中进行,这一系列实验覆盖了各种水流与泥沙条件。在紊流区和层流区的结果都在这里进行介绍,揭示出在每个实验中的一些重要机理。论述的重点是在波浪输沙中的内部不稳定性。     

NUMERICAL ANALYSIS OF THE FLUID FLOW IN A ROTATING CURVED ELLIPTICAL PIPE

A numerical study was conducted for the fully developed laminar flow in rotating curved elliptical pipe. Due to the rotation, the Coriolis force can also contribute to the secondary flow. The interaction of rotation and curvature complicates the flow characteristics. The boundary fitted coordinate was adopted to study the flow characteristic in the rotating systems. The effects of rotation on the flow transition were studied in detail. The generation and mergence of vortices in rotating curved elliptical pipes were also captured for the first time. The simulation results show that the flow for the case of large aspect ratio of the cross-section is more likely to be unstable than that for smaller one.     

INVESTIGATION ON THE FLOW STABILITY OF NEWTONIAN FLUID IN ECCENTRIC ANNULUS VIA THE AXIAL RECIPROCATION OF THE INNER TUBE

The governing equation, together with the formulas of the averaged flux and the stability parameter for Newtonian fluid flowing in eccentric annulus via the axial reciprocation of the inner tube was established in the bipolar coordinate system. Numerical calculation was conducted for the measurement of water flow using the formulas above, of which the results agree well with the experimental data. It is shown that the flow instability can be induced by the increase of the stroke, the frequency, and the eccentricity of annulus, making the sucker rod more susceptible to partial abrasion. Some protecting methods, including adding centralizers, adjusting the stroke and frequency, are proposed to protect the sucker rod from the partial abrasion, and satisfactory results have been achieved in the oilfields.