【作者】 卢占国；

【导师】 姚军；

【作者基本信息】 中国石油大学 ， 油气田开发工程， 2010， 博士

【摘要】 碳酸盐岩储层对世界油气生产作出了重要贡献,但由于强非均质性,储层中流体流动规律至今还没有认识清楚。该研究综合利用物理模拟、数值模拟和理论分析方法,较为系统地研究了缝洞型介质中流体流动规律。取得的主要成果及认识如下:(1)以塔河油田缝洞型储层为基础,将缝洞型油藏储集空间分为六类——广义基质、孤立裂缝网络、孤立溶洞、裂缝网络系统、裂缝-溶洞系统和溶洞系统。(2)提出以福希海默数作为判别缝洞型介质中非达西渗流开始的标准,并利用该标准建立了由达西渗流转换为非达西渗流的临界速度公式,系统分析了缝洞模型中单相临界速度变化特征,在实验研究范围内,单相临界速度随流体粘度和裂缝密度(或连通度、洞密度、洞穴度)增大而增大。(3)根据相对渗透率曲线特征参数和形态,将常见相对渗透率曲线分为六种类型——水相上凹型、水相直线型、水相下凹型、水相上凸型、水相靠椅型和驼背型。研究表明,①在实验驱替速度范围内,由于注入水早期突破导致缝洞型介质中相对渗透率曲线基本为水相下凹型;②束缚水饱和度较低,油相相对渗透率在初期陡直下降,随着含水饱和度的增加,其下降速度逐渐减缓,而水相相对渗透率曲线明显下凹,在高含水相饱和度段其增加幅度越来越小,残余油处所对应的水相相对渗透率最高;③垂直于渗流方向竖直缝数减小或平行于渗流方向竖直缝数增加,都会使裂缝网络模型中残余油饱和度增大,等渗点饱和度减小;④溶洞的存在使残余油饱和度增加;⑤两相流动时不存在固定的临界速度值。(4)采用有限元方法数值研究了缝洞型介质中单相流动形态,①重力作用对溶洞内部流态影响随洞径减小而减小,而对裂缝内部流态影响可以忽略;②当流速增大到某一数值时,溶洞内部出现射流现象。(5)首次采用Level Set方法与N-S方程耦合方法数值研究考虑重力作用下不同洞径、不同洞位置和不同孔喉位置模型内两相流动特征,①洞径越大,缝洞模型最终采出程度越低,缝洞模型中残余油主要存在于溶洞上部空间;②只有一个洞口与主裂缝连通的溶洞,其中的油能否被采出来,取决于洞口的位置,凡是裂缝在洞口上方,则可以靠油水密度差将溶洞中的油驱替出来,反之,溶洞中只有少部分油被驱替出来;③若只有一个孔喉与溶洞连通,不论与其连通缝的方位如何,溶洞内的油都采不出来。该研究成果完善了缝洞型介质流动机理,为进一步认识缝洞型油藏、提高油藏采收率提供理论基础。更多还原

【Abstract】 Carbonate reservoirs have made important contributions to oil and gas production in the world. It is very difficult to understand the fluid flow law in this kind of reservoir because of high heterogeneity. Fluid flow in fractured vuggy media was studied systematically by physical simulation, numerical simulation and theretical analyzation. The main results are as follows: (1) At the beginning of this study, reservoir space of fractured-vuggy reservoirs was divided into six types: generalized matrix, independent fracture network, independent vug, fracture network system, fractured-vuggy system and vug system on the basis of fractured-vuggy in Tahe Oilfield. (2) The Forchheimer number has been used as a criterion to identify the beginning of non-Darcy flow in fractured-vuggy media. And the formula of critical velocity from Darcy flow to non-Darcy was developed based on this criterion. Characteristics of single-phase critical velocity variation in different structural fractured-vuggy models had been analyzed systematically. In the range of experimental studies, single-phase critical velocity increases with fluid viscosity and fracture density (or connectivity, vug density and vug porosity). (3) According to characteristic parameter and shape, relative permeability curves had been divided into six types: water-phase top concave, water-phase straight line, water-phase below concave, water-phase top convex, water-phase chair and humpback.①In the range of experimental displacement rate, most of relative permeability curves in fractured-vuggy models are belong to water-phase below concave due to early breakthrough of injected water.②Residual water saturation is small, and oil relative permeability descended quickly at the beginning and its decline speed gradually slow with water saturation increasing. However, water relative permeability curve showed below concave clearly, water relative permeability increased slowly at high water saturation, and maximum of water relative permeability was at residual oil.③Reduction of vertical fractures perpendicular to fluid flow or augment of vertical fractures parallel to fluid flow will increase the residual oil saturation and decrease the water saturation of isoperm point.④ Existence of vugs will increase the residual oil saturation.⑤Two-phase critical velocity is not a fixed value. (4) Single-phase fluid flow in fractured-vuggy media had been simulated by finite element method.①Effect of gravity on fluid flow decreases with the decrease vug diameter in the vug and can be neglected in fracture.②When velocity increases to a certain numerical, there is similar“jet”phenomenon in vug. (5) Characteristics of two-phase fluid flow under gravity in different vug diameter, vug position and pore throat position models had been numerical studied by level set method coupling with N-S equation at the first time.①Final recovery is lower in fractured model with bigger vug and residual oil presents in the top space of vug.②Whether oil in the vug, where is only one port connected with the main fracture, can be taken out depending on the location of the vug. If fracture is above the vug, oil in the vug can be taken out by the density difference between oil and water. On the contrary, only a little part of oil in the vug can be flooded out.③If there is only one pore throat connected with vugs, the oil in vugs can’t be recovered regardless of orientation of fracture connected with pore throat. The research achievements improved the mechanism of fluid flow in fractured-vuggy media and provide a theoretical basis to further understand the fractured-vuggy reservoir and enhance oil recovery in this kind of reservoir.更多还原