【作者】 穆文志；

【导师】 宋考平；

【作者基本信息】 大庆石油学院 ， 油气田开发工程， 2009， 博士

【摘要】 我国有丰富的低渗透油层资源,但由于受理论与技术发展水平的限制,采收率只能达到20%左右,远低于中、高渗透层水驱—化学驱后采收率可达到60%的指标。造成低渗透油层采收率低的原因很多,根据采收率的定义,波及效率和微观驱油效率决定着采收率的高低。低渗透油层微观驱油效率受孔隙结构、驱替流体性质等诸多因素的影响,研究不同性质流体在多孔介质中的流动规律及其制约低渗透油层微观驱油效率的因素是改善低渗透油层开发效果的关键。低渗透油层孔隙结构复杂、喉道细小、孔喉比大,非达西现象是低渗透油层主要特点。液体在细小流道中流动时受岩石壁面的作用,流动特征、微观作用力及其主导因素发生明显变化。本论文在深入调研国内外关于微流体流动、非达西渗流规律等研究成果的基础上,对水驱油微观机理、多孔介质内微观作用力进行了研究。建立了微孔道内固液相互作用条件下的流体黏性系数表达式、二维流动控制方程及数值方程;研究了收缩-扩张、扩张-收缩两种流道模型的流场分布,分析了不同模型参数条件下的流体流动特征,给出了考虑固液作用、不考虑固液作用两种情况下流体的流动规律;利用应力法确定了孔隙内有效波及效率。主要研究成果如下:通过研究多孔介质内油滴的受力情况,分析了油藏在整个开发过程中流体间作用力的相互关系及其对剩余油分布的影响。特别是考虑了浮力在油藏不同开发阶段对油滴的作用,并应用达西定律研究了流体浮力对垂向剩余油分布规律的影响。结果表明,在油水井中间区域的压力梯度远小于近井区域的压力梯度,而浮力与重力差在油水井间却没有明显变化,导致油滴所受合力的方向同水平方向的夹角变大,油滴向上漂移的趋势增强,容易在油层顶部形成剩余油。为了同固液相互作用条件下流体流动规律进行对比,建立了牛顿流体二维流动控制方程及有限差分数值方程,通过对收缩-扩张、扩张-收缩两种典型流道、不同模型参数的数值计算,研究了相应流道模型的速度、应力及流线分布。结果表明,在相同入口压力梯度的条件下,流道模型参数决定着流道内速度场、应力场、流函数场的分布,分析扩张-收缩流道在相同孔隙半径、不同喉道半径和孔隙长度条件下的计算结果,发现孔喉比和喉道半径是影响流场分布的主要因素,而孔隙长度的影响相对较小;而对于收缩-扩张流道模型,在模型入口压力梯度、孔隙半径不变的情况下,孔喉比、喉道半径、喉道长度对流道内流场分布的影响并不明显。研究了固体与液体分子间的微观作用力,认为固液间的相互作用是形成微孔道边界层的主要因素。流体在半径极其细小的流道中流动时,流体成为边界层流体,其黏度同常规液体的黏度不同,宏观上表现为流体黏度的增加,其值等于流体体相黏度与由固液作用引起的附加黏度之和。通过对微孔道内流体分子的受力分析,给出了微流体的黏性系数表达式,其值为离固体界面距离和固液表面性质的函数。利用所给出的边界层流体黏性系数表达式,建立了二维边界层流体的控制方程及其简化方程,得到了圆形截面毛管和平行窄缝中径向速度分布的近似解。利用有限差分法对二维边界层流体的控制方程进行了离散化,建立了二维边界层方程的数值方程。利用编制的计算机程序,求出了圆形截面毛管中考虑固液作用下流体速度分布的数值解,与前述得到的近似解相比,二者速度分布规律相吻合,证明了考虑固液作用的边界层数值方程及所给边界条件完全正确;利用编制的计算机程序,对流体在收缩-扩张、扩张-收缩两种流道类型内的速度场、应力场、流线场分布进行了数值计算,得到了不同模型参数的流场分布图,与非边界层流体的流动特征相比,考虑固液作用时,流体流速呈数量级减少,孔隙内流体有效波及面积减少,喉道半径越小,固液作用越明显。依据大庆油田真实油藏条件,确定了孔隙模型的几何和流体动力学参数的关系,进而确定了微孔道中原油屈服应力的下限值。根据扩张-收缩流道模型内应力场的计算结果,结合该屈服应力界限值,计算了有效驱油效率,结果表明,孔喉比越大,驱油效率越低。更多还原

【Abstract】 China has abundant resources of low permeability reservoirs, but limited by the current theory and technology development, the recovery can only reach about 20%. This is far below the indicators of the middle and high permeability layer after water flooding - chemical flooding, whose recovery can arrive at 60 %. There are many reasons affect the low recovery in low-permeability reservoirs. According to the definition of recovery, affected efficiency and micro oil displacement efficiency determine the recovery. The micro oil displacement efficiency in low-permeability reservoir is affected by many factors such as pore structure, fluid property of displacement and so on. It is critical to study the flow regulation of different fluids in porous media and the limit factors of micro oil displacement efficiency in low permeability reservoir.Low-permeability reservoir has complex pore structure, small throat and large pore throat ratio, and non-Darcy phenomenon is the main characteristic of low permeability reservoirs. The flow features, the micro-force and its leading factors changed significantly because the liquid is affected by the rock wall while flowing in the sprue. In this paper, based on previous research results of many micro-fluid flow and non-Darcy flow regulation, the micro-mechanism of water displacing oil and the micro force in porous media are studied; and the fluid viscosity coefficient equation in the micro sprue with the interaction of solid and liquid and the two-dimensional flow control equations and numerical equations are given; using the calculation results, the flow field distribution maps of two types of flow channel model, that is, contraction-expansion and expansion-contraction sprue are plotted, the fluid flow characteristics are analyzed under the conditions of different model parameters, and the fluid flow regulation is considered for two cases, that is, considering the role of solid-liquid interaction and without considering the role of solid-liquid interaction; the effective porosity conformance efficiency is determined by the stress method. Research results obtained are as follows:Through the research on the forces of the oil droplets in the porous media, the relationship of forces among the fluids during the whole development of reservoir and the influence of it on the distribution of resident oil are analyzed. Especially, considering the action of buoyancy on the oil droplets in different steps of development of the reservoir, Darcy’s Law is used to study on the influence of the buoyancy of fluid on vertical distribution of resident oil. The result shows that the pressure gradient of the central region between the oil & water wells is far less than that near the well bore region, but the difference of buoyancy and gravity does not change significantly between oil & water wells, resulting in the angle’s becoming larger between the direction of the force that the oil droplets suffered and the horizontal direction. The drift trend upward of oil droplets increased, and it is easy to form the residual oil at the top of the reservoir.In order to be compared with the flow behaviors of the fluid in boundary layer when considering the action between the solid and the liquid, the governing equations and the numerical finite difference equations of the 2-dimentional flow of Newtonian fluid are established, and through the numerical calculation of the convergent-divergent and the divergent-convergent model of flow path and the parameters of these two models, figures of the velocity, the stress and the flow line distribution are plotted. The result shows that under the condition of the same pressure gradient at the inlet, the velocity, the stress and the stream function distribution in the flow path are controlled by the parameters of the model. The calculating result of the divergent-convergent model of flow path with the same radius of pore, different radius of pore throat and different pore length is analyzed, and it is founded that the pore throat ratio and the radius of throat are the main factors which influence the distribution of flow field, while the influence of pore length is relatively little; as to the convergent-divergent model of flow path, with certain pressure gradient at the inlet and pore radius, the influences of the pore throat ratio, the radius of throat and the throat path length on the distribution of flow field in flow path are not obvious.On the basis of the study for solid and liquid microscopic force between molecules,the solid-liquid interaction was considered to be the main factors of the micro porous channel boundary layer of the formations. When fluids flow in extremely small radius of flow channels, the fluid boundary layer become fluids, its viscosity which was different from the conventional liquid viscosity was expressed as the increasing viscosity on the macro, and its value equaled the sum of fluid phase viscosity and solid-liquid effects caused by the additional viscosity. Through the force analysis of the molecules of the boundary layers, a boundary layer expression of fluid viscosity coefficient was given, and its value was a function of the distance from the solid interface and the nature of the solid-liquid surface. Using the expression, a two-dimensional boundary layer flow control equation and its simplified equation were set up, and the circular and rectangular cross-section velocity profile capillary distribution of the approximate solution was acquired as well. By divergence of the two-dimensional boundary layer equations using finite difference method, a numerical equation of the two-dimensional boundary layer equations was set up. Through the programmed computational procedures, the numerical solution of the circular section which considered the solid-liquid capillary flow velocity distribution was given firstly. Compared with the approximate solution above, we found that their speed distribution coincide, therefore we proved the correctness of the boundary layer numerical equation which considered the solid-liquid interaction and boundary conditions; secondly, using the numerical boundary layer equation, two types of pores: contraction-expansion, expansion-contraction, the velocity, stress and flow line fields have been calculated and the flow field distribution maps of different model parameters were acquired. In contrast with the non-boundary layer fluid flow characteristics, we knew that when considering the solid-liquid interaction, the fluid flow rate decreased in magnitude, the effective affected area of fluids within pores reduced, throat radius diminished, and the performance of solid-liquid effect became more significant.Using the relationship among the geometry of pore model and the hydrodynamic parameters derived from the real reservoir conditions in Daqing Oilfield, the lower limit of the yield stress of oil in micro-pore was determined. According to the calculation results of stress in the expansion-contraction sprue and the limit value of this yield stress, the effective displacement efficiency can be calculated. The result shows that the bigger the pore throat ratio, the lower the displacement efficiency.更多还原