【作者】 杨二龙；

【导师】 宋考平；

【作者基本信息】 大庆石油学院 ， 油气田开发工程， 2008， 博士

【摘要】 聚合物驱油作为一项成熟的提高采收率技术,已经在国内尤其是大庆油田实现了工业化应用,在油田稳产、高产中发挥着重要的作用。广大学者对聚合物溶液的渗流理论和驱油机理进行了广泛的研究,并取得了重要认识,但在微观渗流理论和驱油机理方面,现有研究多以室内实验作为主要技术手段。本文调研了大量国内外聚合物驱微观渗流和驱油机理研究成果,以前人工作为基础,用毛管束模型研究了孔隙尺度下非牛顿幂律流体和粘弹性流体的渗流规律,以及聚合物溶液驱油两相流渗流规律。通过亲油岩石壁面油膜受力平衡分析,探索了孔隙尺度下粘弹性聚合物溶液的驱油机理,分析了聚合物溶液驱替微观油膜所需宏观渗流速度。取得的研究成果如下:在幂律流体具有牛顿流体康脱洛维奇变分速度分布形式假设的基础上,通过变分法建立了幂律流体在三角形毛管和矩形毛管内的流量和压降关系式,与本文Matlab数值解和相关文献结果对比表明,变分法结果在较宽的毛管几何尺寸和流体流变参数内具有高精度解,所得流量和压降关系式可应用于孔隙尺度网络模拟和毛管束模型。以单根毛管内幂律流体流量-压降公式为基础,给出了单根毛管和毛管束幂律流体等效渗透率计算方法,计算表明,在截面积相等情况下,圆形毛管和毛管束的等效渗透率最大。应用机械能平衡原理,在Binding的工作基础上,以剪切粘度、拉伸粘度和第一法向应力差作为描述粘弹性聚合物溶液的流变参数,建立了聚合物溶液在收缩、收缩-扩张圆形管道和波纹管内的流量-压降公式。当渗流速度高于某一临界值后,由拉伸应力产生的附加压降将超过剪切压降。对本文研究的聚合物溶液,第一法向应力差对总压降的贡献很小,可以忽略。将多孔介质简化为波纹管组成的毛管束模型,建立了适用于描述粘弹性流体流动特性的渗流模型,与Koshiba等人的室内实验结果对比表明,本文提出的渗流模型可以很好地表征粘弹性聚合物溶液在多孔介质中流动时所表现出的拉伸特性。采用常规毛管束模型和Dong等人提出的Interacting毛管束模型,模拟了水湿条件下牛顿流体的驱油过程。常规毛管束模型由于忽略了渗流过程中的物理特性,在模拟水湿油藏渗流时存在不足,Interacting毛管束模型则很好地弥补了这一缺陷。本文将Dong等人的模型推广应用到非牛顿幂律流体驱油的油水两相流动,并采用阻尼最小二乘法对模型进行了求解,在获得2个以上时间步结果后,把外推线性插值作为下一步运算初值,大大加快了收敛速度。非牛顿幂律流体驱油条件下,幂律指数和稠度系数减小,使不同尺寸毛管中的前缘推进速度差距变大,驱替趋于不均匀,这与吴玉树等人建立的宏观模型在定性规律上是一致的。应用CIR-100界面流变仪,测定了聚合物溶液与原油界面的界面粘度、界面粘性模量和界面弹性模量,三者均随温度的增加先降低而后升高,随聚合物分子量和聚合物溶液浓度的增加而增大,随聚合物溶液矿化度的增加而降低。应用动量平衡原理,分析了界面特性参数对聚合物驱油过程的影响,结果表明,当界面张力低于临界界面张力时,在压力梯度不变的情况下,进一步降低界面张力,可以加快残余油的驱替速度,聚合物驱情况下,油水界面粘度增加,将引起孔隙内残余油驱替速度降低。聚合物驱后荧光分析结果表明,聚合物溶液可以大幅度降低油膜型剩余油。针对这种类型的剩余油,建立了处于油藏流场中,粘附于岩石表面油膜的动力学模型。油膜所受驱油动力为驱油剂流动作用于油膜上的剪切应力和法向应力在油膜表面的积分,所受阻力为油膜变形引起润湿滞后,岩石壁面对油膜的束缚力。在二者达到平衡条件下,给出了水驱和聚合物驱条件下微观油膜启动所需临界流速。分析表明,聚合物溶液由于具有高拉伸粘度,使其能产生高出剪切应力1~2个数量级的拉伸应力,从而更容易使油膜启动。而水驱油时,所产生的拉伸应力几乎可以忽略,剪切应力很难将油膜从岩石表面剥离。更多还原

【Abstract】 Polymer flooding, as a mature technique of enhancing oil recovery, has been industrially used in China, especially in Daqing Oilfileds and has been playing an important role in the stable and high production of oil. Many scholars have made research and obtained significant knowledge in its percolation theory and mechanism of oil displacement. However, in the field of micro-percolation heory and the mechanism of oil displacement, the main technical approach of the current studies is through laboratory experiment. In this paper, through a great deal of research from home and abroad, research was made in the percolation law of non-Newtonian power law fluid and viscoelastic fluid as well as two-phase percolation rule of polymer flooding. Through analysing the stress blance of a single oil drop on the oil wet rock, the mechanism of polymer oil displacement agent was explored and the reason of how polymer fluid could enhanced oil recovery was discovered. The research findings showed as follows:Suppose that power law fluid had similar distribution of Contorovich variational velcoity. Through calculus of variations, the flow drawdown relation of power law fluid in the triangle and rectangle capillaries was established. The result through calculus of variations showed higher precision solution in the bigger capillaries and fluid rheological parameter, compared with Matlab numerical solution and correlated document. Besides, the flow drawdown relation could be used in pore scaling porosity network analog and capillary grouping modeling. On the basis of the flow drawdown relation of power law fluid in a single capillary, calculation methods of effective permeability in a single capillary and capillary grouping were given, which showed that the effective permeability in the circular capillary and tube bundle was among the top in the case of the same cross-section area.On the basis of mechanical energy equilibrium principle and the work of Binding, shear viscosity, extension viscosity and the first direct stress difference were used to describe rheological parameter of viscoelastic polymer fluid. Flow drawdown formulas of polymer fluid in the convergent, convergent divergent circular and sinusoidual capillaries were established. When flow velocity was higher than a certain critical value, pressure drop caused by extensional stress was higher than that caused by shear stress. As to the polymer fluid in this paper, the effect caused by the first direct stress difference on the total pressure drop was too small to ignore.If porous media was considered as sinusoidal capillaries, the percolation model to describe the flow behavior of viscoelastic fluid is established. Compared with the laboratory experiment done by Koshiba, this paper revised the model so that it could better represent the extension character during the flow of viscoelastic polymer fluid in the porous media.Oil displacement process of Newtonian fluid under the water wet condition was simulated through conventional capillary bundle model and Interacting capillary bundle model raised by Dong. Conventional capillary bundle model negleted the physical characteristics during the course of percolation and had its defects when simulating flow in the water wet reservoir. However, Interacting capillary bundle model could well fill the gap. This paper spreaded the application of the model raised by Dong to oil/water two-phase flow of non-Newtonian power law fluid and damped least square method was used to get the solution. During the displacement of non-Newtonian power law fluid, power law exponent and consistency coefficient decreased, which made the gap of frontal velocity get bigger in different sizes of capillaries and made the displacement tend to non-uniform. This is qualitatively in accordance with the macroscopic model raised by Wu Yushu.Through interfacial rheometer CIR-100, interfacial viscosity, interfacial viscosity modulus and interfacial elasticity modulus could be measured. They all decreased and then increased as the temperature rose. Besides, they all increased as the polymer molecular weight and the concentration of polymer fluid rose. With the increasing salinity of polymer fluid, they decreased. Integral momentum balance equation proposed by Slattery is used to study effect of interfaical parameters on polymer flooding process, results shows that for values of interface tension less than the critical value the displacement veloctiy of residual oil will increase as the applied pressure gradient increases and since the increasing of interfacial viscosity in polymer flooding the displacement velocity of residual oil will decrease.Fluorescence analysis of poymer flooding showed that polymer fluid could greatly decrease the oil film remaining oil. As to this type of remaining oil, the dynamic model of a single oil film attaching to the surface of rocks was established in the reservoir flow field.The driving force of the oil film was the integration of shear stress and direct stress on the surface of the oil film when the oil displacement agent flowed through. And resistance force was the wettability hysteresis when the oil film got deformed and the binding force of the surface of rock to oil film. When the driving force was equal to resistance force, critical flow velocities at which the microscopic oil film started to move were given during the water flooding and polymer flooding. The analysis showed that the polymer fluid had high extension viscosity, which could produce extension stress that was higher than shear stress 1~2 order of magnitudes. It benefited the start of the oil film. However, during water flooding, the extension stress could be neglected and the shear stress could hardly exfoliate the oil film from the surface of the rock.更多还原