基于有限元—有限体积方法的裂缝性油藏数值模拟研究
发布时间:2018-03-29 00:22
本文选题:裂缝性油藏 切入点:离散裂缝模型 出处:《西南石油大学》2015年硕士论文
【摘要】:裂缝性油藏资源丰富,开发前景非常广阔。但是由于裂缝性储层介质类型多,尺度变化大,非均质性强,流动规律复杂,对于裂缝性油藏的流动规律及数值模拟已成为当前研究的热点和难点。目前,有关裂缝性油藏渗流模型的理论主要分为三大类:传统的连续介质模型、等效连续模型和离散裂缝网络模型。连续介质模型忽视了裂缝和基质岩块的复杂分布,将基岩和裂缝看作连续介质来近似处理,适合于微裂缝非常发育的裂缝性储层;等效连续模型将复杂的裂缝性储层等效转换为渗透率各向异性的连续介质体,适合于裂缝密集发育的大范围岩体渗流,但是对于非均质性强、尺度变化大的裂缝性储层,其等效渗透率张量计算和表征单元体的判定存在困难;而离散裂缝网络模型考虑了各条裂缝间分布特征和属性参数的差异,能够较为准确地描述裂缝性储层复杂介质分布和渗流规律,逐渐成为近年来研究的重点。 对于偏微分方程的数值解法,有限差分法占有绝对的主导地位。有限差分方法作为一种直接的物理近似,理论简单、物理意义明确,但是网格取向性严重、复杂边界考虑困难、求解精度低等缺点导致其在裂缝性油藏数值模拟中的应用推广受到制约;有限元方法采用积分“弱”形式处理偏微分方程,计算精度高,且易于处理复杂边界;而有限体积方法满足天然的局部物质守恒,避免数值震荡。将有限元和有限体积方法结合起来建立流动方程的数值计算格式优势明显。 因此,针对存在天然大裂缝的强非均质性、多变化尺度裂缝性储层,本文基于离散裂缝网络模型,采用结合有限元-有限体积方法进行求解。围绕此主题开展了以下工作: (1)基于物质平衡原理,结合运动方程、连续性方程和状态方程,推导了油-水两相不混溶、微可压缩流体流动渗流数学方程; (2)利用解耦算法将渗流数学方程分解为压力方程和饱和度方程。基于非结构化网格,采用Galerk.in有限元方法处理压力方程,采用节点中心有限体积方法处理饱和度方程,建立了渗流数学方程的数值计算格式; (3)采用IMPES方法对渗流方程数值计算格式进行求解,并编制了裂缝性油藏有限元-有限体积法数值模拟器; (4)应用有限元-有限体积法数值模拟器对裂缝性油藏注水开发动态进行数值模拟研究,通过单条裂缝直线流动、复杂裂缝系统理论算例和矿场实例计算,验证了本文方法的正确性。 研究表明:裂缝性油藏注水开发水驱前缘的推进速度及方向,受裂缝走向控制,即注入水沿着裂缝延伸方向迅速窜进,与均质油藏相比,裂缝性油藏注水驱前缘突破时间早,含水率上升快,并且在裂缝系统两侧存在剩余油富集区。
[Abstract]:The fractured reservoir is rich in resources and has a very broad prospect of development. However, due to the variety of media types, large scale change, strong heterogeneity and complex flow pattern, the fractured reservoir has a large number of media types. The flow law and numerical simulation of fractured reservoir have become the hot and difficult point of current research. At present, the theory of percolation model of fractured reservoir is divided into three main categories: the traditional continuum medium model. Equivalent continuum model and discrete fracture network model. The continuum model neglects the complex distribution of fractures and matrix blocks, and treats bedrock and fracture as continuous media, which is suitable for fractured reservoirs with very developed microfractures. The equivalent continuum model converts the complex fractured reservoir into a continuum body with permeability anisotropy, which is suitable for a large range of rock mass seepage with dense fractures, but for a fractured reservoir with strong heterogeneity and large scale change. It is difficult to calculate and characterize the unit body by Zhang Liang, and the discrete fracture network model takes into account the differences of the distribution characteristics and attribute parameters of each fracture. It has gradually become the focus of research in recent years to describe the distribution of complex media and the percolation law of fractured reservoirs accurately. For the numerical solution of partial differential equations, the finite difference method plays an absolute dominant role. As a direct physical approximation, the finite difference method is simple in theory and clear in physical meaning, but it has a serious mesh orientation. It is difficult to consider the complex boundary, and its application in the numerical simulation of fractured reservoir is restricted because of its disadvantages such as difficulty in considering the complex boundary, low precision in solving the problem, and the finite element method (FEM) is used to deal with partial differential equations in the form of integral "weak", which has high accuracy. The finite volume method satisfies the conservation of natural local matter and avoids numerical oscillations. The finite element method and the finite volume method are combined to establish the numerical calculation scheme of the flow equation. Therefore, in view of the strong heterogeneity and multi-scale fractured reservoirs with large natural fractures, this paper uses the finite element finite volume method to solve the problem based on the discrete fracture network model. 1) based on the principle of material balance, combined with motion equation, continuity equation and state equation, the mathematical equation of fluid flow in oil-water phase is derived. The seepage mathematical equation is decomposed into pressure equation and saturation equation by decoupling algorithm. Based on unstructured grid, pressure equation is treated by Galerk.in finite element method, saturation equation is treated by node center finite volume method. The numerical calculation scheme of seepage mathematical equation is established. (3) the IMPES method is used to solve the seepage equation and a finite volume finite volume numerical simulator is developed for the fractured reservoir. In this paper, the finite element finite volume method is used to simulate the waterflooding development performance of fractured reservoir, and the theoretical examples of complex fracture system and field examples are used to calculate the flow of single fracture. The correctness of this method is verified. The results show that the advance speed and direction of water flooding in fractured reservoirs are controlled by fracture strike, that is, the injection water flows rapidly along the extended direction of fractures. Compared with homogeneous reservoirs, the breakthrough time of water flooding front in fractured reservoirs is earlier than that in homogeneous reservoirs. The water cut increases rapidly and there are residual oil accumulation areas on both sides of the fracture system.
【学位授予单位】:西南石油大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TE357.6
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