基于三维网络模型的水驱油微观渗流机理研究

利用逾渗网络模型在微观水平进行随机模拟来研究水驱油的微观渗流规律,通过模型计 算结果与油水稳态相对渗透率驱替实验结果对比验证了网络模拟的有效性. 在此基础上,讨 论了在不同润湿条件下、水驱不同阶段的剩余油微观分布规律. 将剩余油分布形态归纳为4 种状态：孤粒/孤滴状、斑块状、网络状和油水混合状态. 研究表明,网络状剩余油的块数 较少,但所占体积比例较大. 随着剩余油饱和度的降低,最大网络状油所占孔隙数减少,剩 余油饱和度在40{\%}$\sim$50{\%}附近开始以较快速度减少. 润湿性不仅影响驱油效率,也影响剩余油分布形态. 在驱替过程中,剩余油分布总的变化趋势是逐渐趋于分散.     

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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.     

气液非混相驱替过程中的卡断机理及模拟研究

研究气液非混相驱替过程中的相界面卡断机理及其影响因素在气驱, 气水交替及泡沫驱等提高油气采收率领域具有重要意义. 本文在原始伪势格子玻尔兹曼模型的基础上, 改进流体-流体作用力格式, 添加流-固作用力, 耦合RK状态方程, 并采用精确差分方法将外力添加到LBM框架中. 通过校准模型的热力学一致性以及模拟测试界面张力, 静态平衡接触角及液相在角隅的滞留等一系列两相体系验证模型的准确性. 基于改进的伪势格子玻尔兹曼模型, 在孔-喉-孔系统中开展气液非混相驱替模拟, 结果表明: 卡断现象与驱替压差, 孔喉长度比及孔喉宽度比有关, 只有当驱替压差处于一定范围内时, 气液两相驱替过程中才会发生卡断现象; 当驱替压差大于临界驱替压差上限时, 即使达到了经典静态准则所预测的卡断条件, 卡断也会被抑制; 当驱替压差小于临界驱替压差下限时, 无法克服毛管“钉扎”作用, 形成无效驱替. 对于固定孔喉宽度比的孔-喉-孔结构, 随着孔喉长度比的增大, 发生卡断现象的驱替压差范围增大; 对于固定孔喉长度比的孔-喉-孔结构, 随着孔喉宽度比的减小, 发生卡断现象的驱替压差范围增大.      

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。     

复杂化学流体在多孔介质中的传质

化学驱油技术已从单一化学剂驱油发展到了复杂化学流体复合体系驱油。化学驱油过程中存在扩散、弥散、吸附、滞留、化学反应等一系列物理化学作用，影响化学剂在多孔介质中的传质过程。碱水驱油实验证明了单一化学剂在多孔介质中存在运移滞后；文中分析了上述物理化学作用，研究了复合体系各种化学剂的运移滞后及滞后差，指出综合吸附作用引起化学剂运移滞后，不同化学剂的运移滞后差导致色谱分离现象。在上述研究的基础上，提出 了吸附对流扩散方程，得到了解析解。并用该解析解处理实验资料，求出了方程中化学剂运移滞后系数和综合扩散系数等相应的参数，可描述和预测复杂化学流体在多孔介质中的传质过程。     

非牛顿流体在非均质油藏渗流压力场实验

在非均质油藏模型上进行非牛顿流体流动物理模拟实验，对比研究水驱、聚合物驱和交联聚合物对提高石油采收率的影响．通过布置高精度的压差传感器测量不同驱替过程模型中的渗流压力场的动态变化，成胶后的交联聚合物封堵了高渗条区，改变了油藏内流体流动方向，驱替出低渗区内油，提高了采收率．     

超临界CO_2-水两相流与CO_2毛细捕获:微观孔隙模型实验与数值模拟研究

CO_2毛细捕获机制是CO_2地质封存中的关键科学问题,然而有关孔隙尺度下(微米极)超临界CO_2毛细捕获的研究较少.采用高压流体-显微镜-微观模型实验装置,开展超临界CO_2条件(8.5 MPa,45?C)下CO_2驱替水(排水)和水驱替CO_2(吸湿)实验,采用高分辨率照相机采集CO_2水两相流运动图像,并借助光学显微镜直接观测孔隙尺度下CO_2毛细捕获特征.同时,采用计算流体动力学方法对实验过程进行三维数值模拟.数值模拟不仅反映了实验过程中两相流驱替锋面的推进过程,还刻画了孔隙尺度下被捕获的CO_2液滴/团簇三维空间形态特征.最后,基于数值模拟给出了CO_2初始饱和度与残余饱和度曲线,即毛细捕获曲线,并对比分析了3种毛细捕获曲线预测模型(即Jurauld模型、Land模型和Spiteri模型)的优劣.分析表明,Jurauld模型的描述能力稍优于Land模型,Spiteri模型的描述能力较弱.由于Land模型只需单个参数,且参数具有明确的物理意义,因此在实际工程中,建议优先采用Land模型.     

水平井两相渗流

研究了水平井两相渗流问题.在流线不变的假定下,给出了水驱油饱和度的二维分布和见水时间公式。两相渗流的见水时间比活塞式驱替的时间快 f(s_t)倍,f(s_t)是含水百分数在前沿处的导数值。     

微重力条件下部分充液贮箱气液界面波动特性的数值模拟

微重力环境中部分充液贮箱内气液界面和气、液两相介质在残余重力或加速度干扰下的运动特征是先进空间流体管理技术的基础. 本文针对空间贮箱常用构型和实际尺寸, 基于邦德数相似准则设计了3个缩比模型, 数值模拟了原型贮箱和缩比模型中加速度变化引起的贮箱内气液两相流动及气液界面上界面波的传播. 数值模拟结果验证了原型和模型间的运动相似性, 发现在满足邦德数相似准则的前提下, 系统还近似满足韦伯数相似准则, 或等价地, 近似满足弗劳德数相似准则. 此外, 数值模拟结果也表明原型和模型间的运动存在细微偏差, 这主要源于黏性耗散作用的差异. 由韦伯数相似准则可知, 缩比加大, 贮箱尺寸减小, 重力突变后由表面张力释放出来的驱动力增强, 相同韦伯数下流动速度增大, 黏性耗散作用随之增强, 本文的数值模拟结果证实了该结论. 相关结果可以用于指导空间贮箱流体管理技术的地面模拟试验的方案设计等.      

基于核磁共振孔隙划分的致密油藏自发渗吸原油可动性研究

自发渗吸驱油是致密油藏提高采收率的有效手段,但不同的孔隙划分方法会导致原油可动性精细定量表征存在差异性.基于此,以鄂尔多斯盆地延长组致密油藏为研究对象,开展了四种典型致密岩心的自发渗吸驱油实验,利用基于核磁共振分形理论的流体分布孔隙精细划分方法,区分了致密砂岩岩心孔隙类型,明确了不同类型岩心孔隙结构对原油可动性和自发渗吸驱油速率的控制特征.研究结果表明不同类型岩心自发渗吸模拟油动用程度介于22.07%～33.26%,核磁共振T2谱双峰型岩心自发渗吸模拟油动用程度高于单峰型岩心;不同类型致密砂岩岩心中流体分布孔隙可初步划分出P1和P2两种类型, P1类型孔隙则可进一步划分出P1-1, P1-2和P1-3三种亚类型孔隙;致密砂岩岩心中P1和P2类孔隙中模拟油均有不同程度的动用, P1类孔隙作为致密岩心中主要孔隙,尤其是P1类孔隙中P1-2和P1-3类孔隙的数量决定了自发渗吸模拟油动用程度;P1-1, P1-2和P1-3类孔隙结构差异性对自发渗吸模拟油动用程度起决定性作用,较小尺寸孔径孔隙较大的孔隙结构差异性不仅提升了自发渗吸模拟油动用程度,而且提升了自发渗吸驱油速率;流体可动性指数较高的P...     

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采用相似准数敏感性分析方法,对各局部相似 模型中所放松相似准数的敏感性进行分析,得到应尽量减少放松的相似准数. 提出了定量评 价局部相似模型优劣的影响系数,通过比较该影响系数的大小即可定量评价各局部相似模型. 结果表明：水驱局部相似模型的精度不仅取决于所满足的相似准数的个数,还与相似准数的 相对放松量有关.     

Sensitivity Analysis of the Dimensionless Parameters in Scaling a Polymer Flooding Reservoir

A set of scaling criteria of a polymer flooding reservoir is derived from the governing equations, which involve gravity and capillary force, compressibility of water, oil, and rock, non-Newtonian behavior of the polymer solution, absorption, dispersion, and diffusion, etc. A numerical approach to quantify the dominance degree of each dimensionless parameter is proposed.With this approach, the sensitivity factor of each dimensionless parameter is evaluated. The results show that in polymer flooding, the order of the sensitivity factor ranges from 10⁻⁵ to 10⁰ and the dominant dimensionless parameters are generally the ratio of the oil permeability under the condition of the irreducible water saturation to water permeability under the condition of residual oil saturation, density, and viscosity ratios between water and oil, the reduced initial oleic phase saturation and the shear rate exponent of the polymer solution. It is also revealed that the dominant dimensionless parameters may be different from case to case. The effect of some physical variables, such as oil viscosity, injection rate, and permeability, on the dominance degree of the dimensionless parameters is analyzed and the dominant ones are determined for different cases.     

Designing of Partial Similarity Models and Evaluation Method in Polymer Flooding Experiment

Based on the scaling criteria of polymer flooding reservoir obtained in our previous work in which the gravity and capillary forces, compressibility, non-Newtonian behavior, absorption, dispersion, and diffusion are considered, eight partial similarity models are designed. A new numerical approach of sensitivity analysis is suggested to quantify the dominance degree of relaxed dimensionless parameters for partial similarity model. The sensitivity factor quantifying the dominance degree of relaxed dimensionless parameter is defined. By solving the dimensionless governing equations including all dimensionless parameters, the sensitivity factor of each relaxed dimensionless parameter is calculated for each partial similarity model; thus, the dominance degree of the relaxed one is quantitatively determined. Based on the sensitivity analysis, the effect coefficient of partial similarity model is defined as the summation of product of sensitivity factor of relaxed dimensionless parameter and its relative relaxation quantity. The effect coefficient is used as a criterion to evaluate each partial similarity model. Then the partial similarity model with the smallest effect coefficient can be singled out to approximate to the prototype. Results show that the precision of partial similarity model is not only determined by the number of satisfied dimensionless parameters but also the relative relaxation quantity of the relaxed ones.     

Effects of Physical Parameter Range on Dimensionless Variable Sensitivity in Water Flooding Reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.The project supported by the Innovative Project of CAS (KJCX-SW-L08) and the National Basic Research Program of China(973)     

用于聚合物驱油的抽油杆动力学分析

聚驱井与水驱井相比杆管偏磨更加严重,聚驱井采出液的法向力是加剧偏磨 的重要因素之一. 根据非牛顿流体力学理论,采用上随体Maxwell模型,建立了法向力计算 模型,确定了井筒内法向力的分布规律,并将此法向力施加在抽油杆的瞬态动力学 模型中; 考虑实际边界条件,采用有限元法对聚驱抽油杆进行了分析计算. 并对FU081801 井模拟计算进行验证,模拟结果与作业检测结果吻合较好,证明了该方法的可行性. 通过此 方法可预测出聚驱井杆管的偏磨位置以及聚合物浓度对抽油杆偏磨的影响程度.     

Theoretical analysis of microscopic oil displacement mechanism by viscoelastic polymer solution

The microscopic oil displacement mechanism in viscoelastic polymer flooding is theoretically analyzed with mechanical method. The effects of viscoelasticity of polymer solution on such three kinds of residual oil as in pore throat, in sudden expansion pore path, and in dead end are analyzed. Results show that the critical radius of mobile residual oil for viscoelastic polymer solution is larger than that for viscous polymer solution, which makes the oil that is immobile in viscous polymer flooding displaced under the condition of viscoelastic polymer solution. The viscous polymer solution hardly displaces the oil in dead ends. However, when the effect of viscoelasticity is considered, the residual oil in sudden expansion pore paths and dead ends can be partly displaced. A dimensionless parameter is suggested to denote the relative dominance of gravity and capillary pressure. The larger the dimensionless parameter, the more accurate the increment expressions.     

水平液─固流中颗粒抑制湍流的行为和条件

用激光多普勒分相测量方法，考察了水平含颗粒水流的主流区，亚毫米颗粒对水流湍流有抑制行为，湍流削弱程度与颗粒浓度、流动发展长度、水流雷诺数等因素有关．按照不出现尾涡脱落和至少能响应一部分大尺度涡的运动这两个基本条件，分析了湍流抑制与有关参量的依赖性．结果表明，流动尺度和颗粒尺寸之比，对于颗粒消耗而不增生湍流起着最主要的作用．在一定的水流雷诺数下，只要这一比值很大，亚毫米颗粒就会表现出对湍流的抑制作用     

Numerical simulation of pore-scale flow in chemical flooding process

Chemical flooding is one of the effective technologies to increase oil recovery of petroleum reservoirs after water flooding. Above the scale of representative elementary volume (REV), phenomenological modeling and numerical simulations of chemical flooding have been reported in literatures, but the studies alike are rarely conducted at the pore-scale, at which the effects of physicochemical hydrodynamics are hardly resolved either by experimental observations or by traditional continuum-based simulations. In this paper, dissipative particle dynamics (DPD), one of mesoscopic fluid particle methods, is introduced to simulate the pore-scale flow in chemical flooding processes. The theoretical background, mathematical formulation and numerical approach of DPD are presented. The plane Poiseuille flow is used to illustrate the accuracy of the DPD simulation, and then the processes of polymer flooding through an oil-wet throat and a water-wet throat are studies, respectively. The selected parameters of those simulations are given in details. These preliminary results show the potential of this novel method for modeling the physicochemical hydrodynamics at the pore scale in the area of chemical enhanced oil recovery.