裂缝性低渗透油藏流-固耦合理论与数值模拟

根据裂缝性低渗油藏的储层特征,建立适合裂缝性砂岩油藏渗流的等效连续介质模型。将渗流力学与弹塑性力学相结合,建立裂缝性低渗透油藏的流-固耦合渗流数学模型,并给出其数值解.通过数值模拟对一实际井网开发过程中孔隙度、渗透率的变化以及开发指标进行计算,并和刚性模型以及双重介质模型的计算结果进行了分析比较.     

致密砂岩逆向渗吸作用距离实验研究

中国致密油储量丰富, 但多数致密储层波及效率低, 衰竭开发效果较差. 逆向渗吸是致密油藏注水开发过程中的一种重要的提高采收率途径, 目前许多学者主要针对致密油藏渗吸采收率及其影响因素开展研究, 而对于渗吸作用距离(表征致密油藏渗吸作用范围)研究较少. 本文采用CT在线扫描装置建立了致密岩心逆向渗吸作用距离量化方法, 明确了逆向渗吸的作用范围, 进一步研究了流体压力、含水饱和度、岩心渗透率和表面活性剂对逆向渗吸作用距离的影响, 阐明了逆向渗吸作用距离与渗吸采收率的关系, 为提高致密油藏采收率提供指导. 研究结果表明, 渗透率为0.3 mD的致密岩心逆向渗吸作用距离尺度仅为1.25 ~ 1.625 cm; 5 MPa条件下渗透率为0.302 mD的岩心逆向渗吸作用距离为1.375 cm. 在本实验条件下, 流体压力和初始含水饱和度对致密岩心逆向渗吸作用距离的影响较小, 而渗透率和表面活性剂对致密岩心逆向渗吸作用距离的影响显著, 渗透率为0.784 mD的岩心逆向渗吸作用距离相较于渗透率为0.302 mD的岩心提高2.63倍. 逆向渗吸作用距离是渗吸采收率表征的重要参数, 决定了逆向渗吸作用的波及范围.      

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根据岩心实验提出了两参数的非线性渗流方程,并在此基础上结合Buckly-Leverett 方程建立了非线性非混相驱替方程. 通过对该方程求解分析可知,与线性达西渗流相比,非 线性渗流的驱油相率较差;同一含水饱和度下的含水率更高;而储层中各点的压力梯度更大, 导致所需注采压差更大. 说明有效的开发低渗透油藏需要比中高渗油藏更小的井距和更高的 注采压力体系.     

天然气驱长岩心室内实验研究

低渗透油藏注水开发效果差、采收率低,而采用气驱技术是动用此类难采储量的有效方法之一。本文利用长岩心实验模型,进行了物理模拟研究,得到了该油藏在纯气驱、纯水驱、完全水驱后气水交替驱、原始状态下气水交替驱和油藏目前注水倍数下气水交替驱等方式下的采收率和压力等变化情况,为油藏选择合理的开采方式提供了依据,并且为进一步的数值模拟工作提供了基础数据。     

具有弱夹层的封闭油藏中的瞬态渗流

多层油藏分为层间无窜流的油藏和层间有窜流的油藏。本文研究了层间有弱渗透夹层的两层油藏中两种情形的瞬态渗流,包括单层打开的瞬态渗流和一层注入、一层采出的两层油藏的瞬态渗流。用面积平均方法求出了弱渗透夹层封闭油藏中瞬态渗流的平均压降。分析表明:在渗流前期,层间窜流量逐渐增大,在后期层间窜流量趋于稳定;在单层开采的情况下:初期两层压降不同,非打开层的压降有滞后现象,并且隔层渗透率越小,油井工作强度越弱,滞后时间越长;后期两层压降趋于一致,可以作为一层油藏处理。在一注一采的油藏中,当注采量相同时,两层压降在后期趋于不同的稳定值;当注采量不同时,两层压降在后期趋于一致,但不能达到稳定。     

地下岩体的垂向渗透率测试及分析

本文介绍了在真实油井中使用阵列压力计测量油藏薄层垂向渗透率的实验方法。通过注水-停注并多次重复此过程使地层产生压差,并在井中不同深度放置压力计接收压力信号。为分析压力的变化,本文从渗流力学基本方程出发,对其无量纲化并采用Laplace变换及数值反变换技术,得到考虑垂向渗透率的地层压力分布表达式,利用这一表达式,对测试的压力资料进行解释。最后根据非线性回归理论对其中的4只压力计的压力资料进行分析,得到了各层垂向渗透率。     

动边界双重介质油藏低速非达西渗流试井模型

裂缝性油藏中基质岩块的渗透率一般很低,大量岩心测试实验证实在基质岩块内的液体渗流和在一定含水饱和度下的气体渗流将偏离达西渗流,往往出现低速非达西渗流,表现出启动压力梯度以及流体流动边界不断向外扩展等特殊现象。本文充分考虑启动压力梯度与动边界的影响,建立了微可压缩双重介质油藏低速非达西渗流的试井数学模型,对时间和空间变量...     

含泥质夹层油藏蒸汽注采过程的自适应网格算法研究

根据泥质夹层的低渗特性及空间分布，本文提出了一种含泥质夹层油藏网格渗透率的粗化计算方法，并在此基础上，将自适应网格算法应用于含泥质夹层油藏的数值模拟，提升其计算效率．在计算过程中，网格的动态划分仅依据流体物理量的变化，泥质夹层区域不全部采用细网格，仅针对流动锋面处的泥质夹层采用细网格，其余泥质夹层处采用不同程度的粗网格．相较于传统算法，网格数大幅下降．数值算例表明，自适应网格算法的计算结果精度与全精细网格一致，能够准确模拟出泥质夹层对于流体的阻碍作用，同时计算效率得到大幅提升，约为全精细网格算法的3~7 倍．     

聚合物注入能力的实验研究

聚合物驱油作为一种重要的三次采油方法,在国内外油气田开发中得到了广泛应用.聚合物驱油效果的好坏取决于多种因素,其中很重要的一个因素是聚合物的注入能力,这一因素直接决定了聚合物驱油的成败.本文利用实验方法研究了聚合物的分子质量、岩样的渗透率以及注入速度等因素对聚合物注入能力的影响.结果表明,聚合物溶液具有粘弹性,注入速度增大,注入性变差.同时聚合物分子量越大,岩心渗透率越低,聚合物注入性越差.对于孤岛中一区,平均孔隙半径与聚合物分子折算半径之比大于10时,聚合物可顺利注入地层.研究结果可用于指导现场聚合物的选取,从而有效保证聚合物的注入能力,使聚合物驱油达到预期效果.     

基于孔与裂隙网络模型的平行微裂隙对驱油的影响规律研究

认识双重多孔介质中油水两相微观渗流机制是回答形成什么类型的裂隙网络可提高油藏采收率的关键. 微裂隙的分布可以提高多孔介质的绝对渗透率,但对于基质孔隙中的流体介质,微裂隙的存在会引起多孔介质中局部流体压力和流场的变化,导致局部流动以微裂隙流动为主,甚至出现窜流现象,降低驱油效率. 本文基于孔与裂隙双重网络模型,在网络进口设定两条平行等长且具有一定间隔的微裂隙,分析微裂隙的相对间隔(微裂隙之间距离/喉道长度)和微裂隙相对长度(微裂隙长度/喉道长度)对于微观渗流特征的影响. 结果表明:随微裂隙相对长度的增加,出现驱油效率逐渐降低,相对渗透率曲线中的油水共渗区水饱和度和等渗点增加,油水两相的共渗范围减小等现象;随着微裂隙之间相对间隔增大,周围越来越多的基质孔穴间的压力差减小,在毛管压力的限制下,驱替相绕过这些区域,而导致水窜现象.      

带式输送机的动张力计算与动力学设计

给出了带式输送机在采用不同拉紧装置时胶带黏弹性振动方程的位移解和动张力解析解的计算方法，给出了拉紧装置、驱动装置和制动装置的动力学设计方法，并研究了限制或消除胶带弹性振动的工程设计方法。     

METHOD BASED ON DUAL-QUADRATIC PROGRAMMING FOR FRAME STRUCTURAL OPTIMIZATION WITH LARGE SCALE

The optimality criteria (OC) method and mathematical programming (MP) were combined to found the sectional optimization model of frame structures. Different methods were adopted to deal with the different constraints. The stress constraints as local constraints were approached by zero-order approximation and transformed into movable sectional lower limits with the full stress criterion. The displacement constraints as global constraints were transformed into explicit expressions with the unit virtual load method. Thus an approximate explicit model for the sectional optimization of frame structures was built with stress and displacement constraints. To improve the resolution efficiency, the dual-quadratic programming was adopted to transform the original optimization model into a dual problem according to the dual theory and solved iteratively in its dual space. A method called approximate scaling step was adopted to reduce computations and smooth the iterative process. Negative constraints were deleted to reduce the size of the optimization model. With MSC/Nastran software as structural solver and MSC/Patran software as developing platform, the sectional optimization software of frame structures was accomplished, considering stress and displacement constraints. The examples show that the efficiency and accuracy are improved.     

One-Dimensional Consolidation of Layered and Visco-Elastic Soils under Arbitrary Loading

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电动汽车电驱动系统振动特性分析

论文以某电动汽车为研究对象,采用理论与数值相结合的方法对电动汽车电驱动系统的振动特性进行研究．首先将整车模型划分为转子、定子、副车架、车身子结构及多个连接子结构;然后给出了电驱动系统电磁转矩和电磁径向力的解析表达式,采用模态综合法建立整车的非线性动力学模型,并对其响应特性进行分析．为了验证模型的正确性,论文还采用有限元法对系统的动力学特性进行仿真,仿真结果与理论结果具有较好的一致性;最后采用该模型分析了极弧系数和气隙长度对电驱动系统振动特性的影响以及电机悬置对车身振动的影响．论文研究对认识电动汽车电驱动系统的振动特性具有重要的促进作用．     

无虚拟节点的有限元界面协调技术

分析了罚函数虚拟节点位移协调法，在此基础上提出了无虚拟节点罚函数位移协调法，推导了该界面协调技术的耦合公式，解决了网格突变情况下的位移协调问题，从而协调了计算精度与效率间的矛盾。通过算例分析，验证了其合理性，结果表明所提出的方法的刚度矩阵具有对称性、带状性，同时该法还有精度高、计算效率高等优点。     

Quasi-static analysis of forces and stress for a novel two-step movable tooth drive

For sine movable tooth drive, the movable tooth number must be increased to obtain large speed ratio of the drive which increases largely radial size of the drive. Here, a novel two-step movable tooth drive is proposed. The drive can realize small size and large speed ratio simultaneously. For the two-step movable tooth drive, 3D design was done; the forces and the contact stress in the drive system were investigated; results show that the maximum force on the second step drive depends on radius of the movable teeth, size parameters of the second step drive, and radius of the sine ball track in the first step drive; the contact stresses between the meshing elements change periodically, the contact stress between the movable teeth and cap end is the maximum which can be taken as design factor for the load-carrying ability of the drive system.     

Numerical Analysis of Imbibition Front Evolution in Fractured Sandstone under Capillary-Dominated Conditions

Fractures serve as primary conduits having a great impact on the migration of injected fluid into fractured permeable media. Appropriate transport properties such as relative permeability and capillary pressure are essential for successful simulation and prediction of multi-phase flow in such systems. However, the lack of a thorough understanding of the dynamics governing immiscible displacement in fractured media, limits our ability to properly represent their macroscopic transport properties. Previous experimental observations of imbibition front evolution in fractured rocks are examined in the present study using an automated history-matching approach to obtain representative relative permeability and capillary pressure curves. Predicted imbibition front evolution under different flow conditions resulted in an excellent agreement with experimental observations. Sensitivity analyses, in combination with direct experimental observation, allowed exploring the competing effects of relative permeability and capillary pressure on the development of saturation distribution and imbibing front evolution in fractured porous media. Results show that residual saturations are most sensitive to matrix relative permeability to oil, while the ratio of oil and water relative permeability, rock heterogeneity, boundary condition, and matrix–fracture capillary pressure contrast, affect displacement shape, speed, and geometry of the imbibing front.     

Effects of Fines Migration on Low-Salinity Waterflooding: Analytical Modelling

We discuss the governing system for oil–water flow with varying water composition. The model accounts for wettability alteration, which affects the relative permeability, and for salinity-variation-induced fines migration, which reduces the relative permeability of water. The overall ionic strength represents the aqueous phase composition in the model. One-dimensional displacement of oil by high-salinity water followed by low-salinity-slug injection and high-salinity water chase drive allows for exact analytical solution. The solution is derived using the splitting method. The analytical model obtained analyses the effects of wettability alteration and fines migration on oil recovery as two distinct physical mechanisms. For typical reservoir conditions, the significant effects of both mechanisms are observed.