非均质油藏多相流模拟的升尺度方法

Geological characterizations usually contain a large number of cells in fine scale reservoir descriptions, which makes the storage and computation of reservoir simulation quite challenging. An appropriate upscaling and coarsening method would significantly reduce the number of grid blocks and improve efficiency, and thus is very helpful for reservoir development and optimization. However, the accuracy and speed of previous upscaling methods require further improvement, especially for multiphase flow in heterogeneous formations..This project will focus on heterogeneous formations with high permeability channels such as fluvial systems, and propose new upscaling methods for multiphase flow simulations, on the goal of high accuracy and efficiency. We will develop two approaches: 1. change current methods, improve the accuracy of the pressure and saturation boundary conditions of the coarse grids, and obtain more accurate absolute and relative permeabilities; 2. adopt new ideas, represent the fine scale reservoir descriptions as multi-media models including fracture and matrix, which is closer to the real conditions and significantly improve computational efficiency since the local multiphase simulations are omitted. In sum, this project aim for accurate and efficient upscaling methods for multiphase flow simulations in heterogeneous formations, which is of great benefit to reservoir simulation, production and development in China.

在精细油藏描述过程中，地质建模一般包含大量的网格，对计算机的存储和运算能力都是很大的挑战。合理的升尺度和网格粗化方法能够极大地减少网格数量，降低模拟难度，提高计算效率，对油藏开发优化有着重要的意义。但是现有的升尺度方法在处理非均质油藏多相流过程时，精度和速度都有待提高。.本项目将以河流相等含高渗透率通道的非均质油藏为主要研究对象，提出新的多相流模拟升尺度方法。拟研究以下两个方案：一、改进现有方法，提高粗网格压力和饱和度边界条件的精度，得到更准确的粗化渗透率和相渗曲线；二、发展新的思路，将精细油藏粗化为多重介质模型，分为裂缝和基质等来处理，更接近真实物理情况，且无需求解局部多相流过程，极大地提高运算效率。综上所述，本项目旨在提出准确高效的非均质油藏多相流模拟的升尺度新方法，为我国油藏数值模拟和实际生产开发提供帮助。

现代地质建模技术通过高分辨率网格表示各向异性的异质地层，网格数量巨大，计算负担很重，需要尺度升级的方法。该方法将在精细系统中定义的属性放大到在粗尺度系统中定义的等效属性。一般而言，解析方法非常有效，但仅限于假设和近似，而数值方法虽然更耗时，但更为稳健。在这项工作中，我们开发了一种解析方法来近似有限差分格式的数值解与周期边界条件。利用摄动展开技术和傅立叶分析，考虑到空间的非均匀性和各向异性，以及网格块的几何结构，该方法生成了张量等效导水率的显式公式。它适用于具有不同协方差/变量模型和各种对数导水率方差，相关长度，旋转角度，细网格导水率的各向异性比率，细网格尺寸的各向异性比率以及精细网格块数量的各种情况。该分析方法与用于估算导水率张量，水头和排放速度的数值方法很好地吻合。对于任何给定的统计量，解析方法中的系数只需要计算一次，这使得所提出的方法比数值方法非常高效。